Internet DRAFT - draft-dcsgroup-sip-arch
draft-dcsgroup-sip-arch
SIP Working Group W. Marshall
Internet Draft AT&T
Document: <draft-dcsgroup-sip-arch-06.txt>
Category: Informational K. Ramakrishnan
TeraOptic Networks
E. Miller
Terayon
G. Russell
M. Osman
CableLabs
B. Beser
Juniper Networks
M. Mannette
K. Steinbrenner
3Com
D. Oran
F. Andreasen
Cisco
J. Pickens
Com21
P. Lalwaney
Nokia
J. Fellows
Copper Mountain Networks
D. Evans
D. R. Evans Consulting
K. Kelly
NetSpeak
February 28, 2002
Architectural Considerations for Providing Carrier Class Telephony
Services Utilizing SIP-based Distributed Call Control Mechanisms
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026[1].
DCS Group Category: Informational - Expiration 8/31/02 1
DCS Architecture February 2002
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts. Internet-Drafts are draft documents valid for a maximum of
six months and may be updated, replaced, or obsoleted by other
documents at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
1. Abstract
This document provides an overview of a SIP-based Distributed Call
Signaling (DCS) architecture to support carrier class packet-based
voice, video, and other real time multimedia services. Companion
documents address a specific set of SIP 2.0 protocol extensions and
usage rules that are necessary to implement the DCS architecture in
an interoperable fashion.
The DCS architecture takes advantage of endpoint intelligence in
supporting telephony services without sacrificing the network's
ability to provide value through mechanisms such as resource
management, lookup of directory information and translation
databases, routing services, security, and privacy enforcement. At
the same time, the architecture provides flexibility to allow
evolution in the services that may be provided by endpoints and the
network.
DCS also takes into account the need to manage access to network
resources and account for resource usage. The SIP usage rules
defined in the accompanying IDs specifically address the
coordination between Distributed Call Signaling and dynamic quality
of service control mechanisms for managing resources over the access
network. In addition, the DCS architecture defines the interaction
needed between network provided call controllers, known as a "DCS-
proxy" for supporting these services.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC-2119 [2].
DCS Group Category: Informational - Expiration 8/31/02 2
DCS Architecture February 2002
3. Table of Contents
1. Abstract........................................................2
2. Conventions used in this document...............................2
3. Table of Contents...............................................3
4. Introduction....................................................4
4.1 Background and Motivation......................................4
4.2 Requirements And Design Principles............................6
4.3 Distributed Call Signaling Architecture........................7
4.4 Trust Boundary................................................10
4.5 Basic Call Flow...............................................10
5. Resource Management............................................13
6. Distributed Call State.........................................14
7. DCS Proxy - DCS Proxy Communications...........................16
8. Privacy........................................................17
9. Security Considerations........................................19
10. Call Flows....................................................19
10.1 Basic Call Flow from MTA to MTA..............................20
10.2 Basic Call Flow from MTA to CMS..............................34
10.3 Basic Call Flow from CMS to MTA..............................43
10.4 Basic Call Flow from CMS to CMS..............................52
10.5 Call-Forwarding-Unconditional and Call-Forwarding-Busy.......59
10.6 Call-Forwarding-No-Answer....................................65
10.7 Call-Forwarding-MTA-Unavailable..............................71
10.8 Return-Call..................................................73
10.9 Customer-Originated-Trace....................................77
10.10 Call-Waiting................................................79
10.11 Call-Transfer-Blind.........................................85
10.12 Call-Transfer-Consultative..................................92
10.13 Three-Way-Calling (with Network Bridge)....................100
10.14 Three-Way-Calling Hangup sequences.........................110
10.15 CODEC Change within previous authorization.................116
10.16 CODEC Change requiring new authorization...................118
10.17 Busy-Line-Verification.....................................125
10.18 Operator break-in..........................................128
10.19 Lawfully Authorized Electronic Surveillance................130
10.19.1 Call-Forwarding-Unconditional with Forwarder under
Surveillance.....................................................131
10.19.2 Call-Transfer-Blind with Transferer under Surveillance...135
10.19.3 Call-Transfer with new destination unable to do interception
.................................................................140
10.19.4 Call-Transfer-Consultative with Transferer under
Surveillance.....................................................141
10.20 Privacy with Application-level Anonymizer..................146
11. Notice Regarding Intellectual Property Rights................163
12. References...................................................163
13. Acknowledgements.............................................164
14. Author's Addresses...........................................164
Full Copyright Statement.........................................167
4. Introduction
DCS Group Category: Informational - Expiration 8/31/02 3
DCS Architecture February 2002
This document provides an overview of a SIP-based Distributed Call
Signaling (DCS) architecture to support carrier class packet-based
voice, video, and other real time multimedia services. The DCS
architecture and the corresponding SIP protocol enhancements
(described in companion documents) are being developed as part of
the cable industry's PacketCable initiative, managed out of
CableLabs (see www.cablelabs.com). PacketCable is defining a series
of interface specifications that will enable vendors to develop
interoperable products for providing internet telephony and other
multimedia services over DOCSIS-enabled cable data networks.
The DCS architecture described herein has its roots in the DOSA work
performed by AT&T Laboratories ["Distributed Open Signaling
Architecture"; Kalmanek, Marshall, Mishra, Nortz, Ramakrishnan, et
al.; October, 1998]. A relatively large group of vendors have
cooperated in an intensive effort to develop the DCS architecture
and SIP protocol extensions described here and in the accompanying
protocol drafts. Although DCS was originally designed with cable
access networks in mind, the SIP signaling enhancements have general
applicability to carrier class VOIP services running over QoS
enabled IP networks.
The authors are submitting this draft to the IETF in order to
provide general information regarding the DCS architecture and to
convey the motivation behind the SIP enhancements recommended in the
accompanying protocol drafts. We believe that incorporation of the
concepts and mechanisms described in this set of drafts by the IETF
into the SIP standard will significantly enhance SIP's ability to
function as a carrier-class signaling protocol. Such an enhancement
to SIP would undoubtedly aid in its widespread acceptance and
deployment. We have incorporated several useful comments received at
the IETF SIP Working group on earlier versions of this and the other
DCS related drafts.
The PacketCable Draft Specification for DCS is available from the
CableLabs website at:
ftp://ftp.cablelabs.com/pub/ietfdocs/dcsdraft2.pdf.
4.1 Background and Motivation
The design of the Distributed Call Signaling (DCS) architecture
recognizes the trend towards use of packet networks as the
underlying framework for communications. These networks will
provide a broad range of services, including traditional best-effort
data service as well as enhanced, value-added services, such as
telephony. At the same time, improvements in silicon will reinforce
the trend towards increased functionality in endpoints. These
intelligent endpoints will take advantage of the widespread
availability of packet networks to enable a rich set of applications
and services for users.
DCS Group Category: Informational - Expiration 8/31/02 4
DCS Architecture February 2002
However, when the network is used for real-time telephony
applications, it is essential to have service differentiation at the
IP layer. The ability to control and monitor usage is needed for
the provider to be able to provide service differentiation and to
derive revenue from the enhanced services. At the same time, the
availability of best effort communications and the migration of
functionality to the endpoints pose a challenge to the provider to
find incentives for users to use or pay for enhanced services.
We see three key functions that a provider can offer, as incentives
to use enhanced services. First, the network service provider has
the unique ability to manage and provide network layer quality of
service. When users depend on the quality of the service, as with
telephony, there is a strong incentive to use the enhanced service,
rather than a best effort service. Second, the network service
provider can play an important role as a trusted intermediary. This
includes ensuring the integrity of call routing, as well as ensuring
both the accuracy and the privacy of information that is exchanged.
The service provider can also add value by ensuring that services
are provided consistently and reliably, even when an endpoint is
unavailable. Finally, there are a number of services that may be
offered more efficiently by the network service provider rather than
in endpoints. For example, conference bridging may be more cost
effective to implement in a multi-point bridge rather than in every
endpoint attached to the network.
A key contribution of the DCS architecture is a recognition of the
need for coordination between call signaling, which controls access
to telephony specific services, and resource management, which
controls access to network-layer resources. This coordination is
designed to meet the user expectations and human factors associated
with telephony. For example, the called party should not be
alerted until the resources necessary to complete the call are
available. If resources were not available when the called party
picked up, the user would experience a call defect. In addition,
users expect to be charged for service only after the called party
answers the phone. As a result, usage accounting starts only after
the called party picks up. Coordination between call signaling and
resource management is also needed to prevent fraud and theft of
service. The coordination between DCS and Dynamic QoS protocols
ensures that users are authenticated and authorized before receiving
access to the enhanced QoS associated with the telephony service.
It is important to be able to deploy a residential telephone service
at very large scale, cost-effectively. To achieve this, DCS
minimizes the messaging overhead on network call servers, and does
not require these servers to maintain call state for active calls.
Once a call is established, call state is maintained only where it
is needed, in keeping (informally) with the principle of "fate-
sharing" at the endpoints that are involved in the call, and at the
Edge Routers in the bearer path that are providing differentiated
service to the media flow. This allows the network call servers to
DCS Group Category: Informational - Expiration 8/31/02 5
DCS Architecture February 2002
scale to support more users, and imposes less stringent reliability
requirements on those servers.
DCS is also designed so that calling users receive consistent
service even when a called endpoint is unavailable. For example,
when an endpoint is unavailable service logic in a network call
server can forward telephone calls to a voice mailbox.
4.2 Requirements And Design Principles
In this section, we briefly describe the application requirements
that led to a set of DCS signaling design principles. In its most
basic implementation, DCS supports a residential telephone service
comparable to the local telephone services offered today. In
addition to the commonly used service features that need to be
supported, there are important requirements in the areas of
reliability, performance, and scalability that influence the
signaling architecture. Supporting an IP telephony service
comparable to the telephony service offered today requires enhanced
bearer channel and signaling performance, including:
. Low delay - end-to-end packet delay must be small enough that it
does not interfere with normal voice conversations. The ITU
recommends no greater than 300 ms roundtrip delay for telephony
service.
. Low packet loss - packet loss must be small enough to not
perceptibly impede voice quality or performance of fax and voice
band modems.
. Short post-dial delay - the delay between the user dialing the
last digit and receiving positive confirmation from the network
must be short enough that users do not perceive a difference with
post-dial delay in the circuit switched network or believe that
the network has failed.
. Short post pickup delay - the delay between a user picking up a
ringing phone and the voice path being cut through must be short
enough so that the "hello" from either the initiator or the
receiver of the call is not clipped.
We identify a number of key design principles that arise from the
requirements and philosophy outlined above.
1. Providing differentiated network-layer quality of service is
essential, while allowing the provider to derive revenues from the
use of such differentiated services.
2. The architecture should allow, and even encourage, implementation
of services and features in the intelligent endpoints, where
economically feasible, while still retaining value in the network
and network-based services
DCS Group Category: Informational - Expiration 8/31/02 6
DCS Architecture February 2002
3. The architecture must ensure that the network is protected from
fraud and theft of service. The service provider must be able to
authenticate users requesting service and ensure that only those
authorized to receive a particular service be able to obtain it.
4. The architecture must enable the service provider to add value by
supporting the functions of a trusted intermediary. This includes
protecting the privacy of calling and called party information,
and ensuring the accuracy of the information that is provided in
messages from the network.
5. The architecture must enable the service provider to give a
consistent view of basic services and features even when customer
premise equipment is unavailable, and allow users to take
advantage of functionality that is provided in the network, when
it is cost-effective and easy to use.
6. The architecture must be implementable, cost-effectively, at very
large scale.
4.3 Distributed Call Signaling Architecture
The Distributed Call Signaling Architecture follows the principles
outlined above to support a robust telephony service. Figure 1
introduces the key components in the architecture.
The architecture assumes a broad range of DCS-compliant endpoints
that provide telephony service to the user including Media Terminal
Adapters (MTAs) that may be integrated with a Cable Modem or is a
standalone device, as well as other endpoints such as personal
computers. The access network interfaces to an IP backbone through
a system we refer to as the Edge Router (ER). The ER is the first
trusted element within the provider's network and is considered to
be the edge of the network for providing access to differentiated
quality of service. We believe that the access network is likely to
manage resources on a per-flow basis, with associated signaling
mechanisms (such as RSVP). The ER performs resource management, acts
as a policy enforcement point and as a source of billing
information.
DCS-proxies (DPs) process call signaling messages and support number
translation, call routing, feature support and admission control.
In the context of SIP, a DCS-proxy is a SIP proxy that is involved
in processing and forwarding of SIP requests. DPs act as trusted
decision points for controlling when resources are committed to
particular users. Media servers represent network-based components
that operate on media flows to support the service. Media servers
perform audio bridging, play terminating announcements, provide
interactive voice response services, etc. Finally, PSTN gateways
interface to the Public Switched Telephone Network.
DCS Group Category: Informational - Expiration 8/31/02 7
DCS Architecture February 2002
+-----+
| MTA | MTA: media terminal adapter
+-----+
| ER: Edge Router
Access Network |
|
+----+
| ER |
+----+
| +-----------+
|----| DCS Proxy |
| +-----------+
|
| +------------+
Backbone Network |----|Media Server|
| +------------+
|
| +------------+
|----|PSTN Gateway|
| +------------+
+----+
| ER |
+----+
|
Access Network |
|
+-----+
| MTA |
+-----+
Figure 1: A Simple view of Components of an IP Telephony
Architecture used in a HFC Cable Environment.
Telephony endpoints are considered to be "clients" of the telephony
service. Consistent with the design principles, the architecture
allows a range of services to be implemented by intelligent
endpoints. They collect dialed digits, participate in signaling and
contain the service logic required for basic call setup and feature
support. Endpoints also participate in end-to-end capability
negotiation. However, endpoints are not trusted to provide accurate
information to the network or to keep information that is received
private, except when it is in the endpoint's best interests to do
so.
Access to network resources on a differentiated basis is likely to
be controlled by the service provider. The ER receives resource
management requests from endpoints, and is responsible for ensuring
that packets are provided the QoS they are authorized to receive
(either through packet marking, or through routing and queueing the
packets as a specific QoS assured flow). The ER requires
authorization from a network entity (on a call-by-call basis for the
DCS Group Category: Informational - Expiration 8/31/02 8
DCS Architecture February 2002
telephony service) before providing access to enhanced QoS for an
end-to-end IP flow. The obvious point where this policy and control
function resides is the DCS-proxy (also called a gate-controller,
because of this responsibility for managing access to enhanced QoS).
Thus, the ER is able to ensure that enhanced QoS is only provided
for end-to-end flows that have been authorized and for which usage
accounting is being done. Since the ER knows about the resource
usage associated with individual IP flows, it generates the usage
events that allow a user to be charged for service.
We introduce the concept of a "gate" in the ER, which manages access
to enhanced quality of service. The gate is a packet classifier and
policer that ensures that only those IP flows that have been
authorized by the DCS-proxy are granted access to enhanced QoS in
the access and backbone networks. Gates are "opened" selectively
for a flow. For the telephony service, they are opened for
individual calls. Opening a gate involves an admission control
check that is performed when a resource management request is
received from the endpoint for an individual call, and it may
involve resource reservation in the network for the call if
necessary. The packet filter in the gate allows a flow of packets to
receive enhanced QoS for a call from a specific IP source address
and port number to a specific IP destination address and port
number.
The DCS-proxy, in addition to implementing many of the call control
functions, is responsible for the policy decision regarding whether
the gate should be opened. DCS sets up a gate in advance of a
resource management message. This allows the policy function, which
is at the DCS-proxy, to be "stateless" in that it does not need to
know the state of calls that are already in progress.
DCS-proxies are typically organized in domains. A DCS-proxy is
responsible for a set of endpoints and the associated ERs. While
endpoints are not trusted, there is a trust relationship between the
ER and its associated DCS-proxy, since the DCS-proxy plays a role as
a policy server controlling when the ER can provide enhanced QoS
service. There is also a trust relationship among DCS-proxies.
Details of the security model are outside the scope of this draft.
The DCS-proxy is designed as a simple transaction server, so that
the failure of a DCS-proxy does not affect calls in progress. A
domain will likely have a primary and one or more secondary DCS-
proxies. If the primary DCS-proxy fails, only calls in a transient
state are affected. The endpoints involved in those calls will time
out and retry. All active calls are unaffected. This is possible
because the DCS-proxy retains no call state for stable calls. We
believe this design makes the DCS-proxy efficient and highly
scalable, and keeps the reliability requirements manageable.
DCS supports inter-working with the circuit switched telephone
network through PSTN gateways. A PSTN gateway may be realized as a
combination of a media controller, media gateway, and a signaling
DCS Group Category: Informational - Expiration 8/31/02 9
DCS Architecture February 2002
gateway. A media gateway acts as the IP peer of an endpoint for
media packets, converting between the data format used over the IP
network and the PCM format required for transmission over the PSTN.
The signaling gateway acts as the IP peer of an endpoint for
signaling packets, providing signaling inter-working between DCS and
conventional telephony signaling protocols such as ISUP/SS7. A media
gateway control protocol is used to control the operation of the
media gateway from the signaling gateway.
There are additional system elements that may be involved in
providing the telephony service. For example, the DCS-proxy may
interface with other servers that implement the authorization or
translation functions. Similarly, three way calling may be
supported using media servers in the network.
4.4 Trust Boundary
The DCS architecture defines a trust boundary around the various
systems and servers that are owned, operated by, and/or controlled
by the service provider. These trusted systems include the proxies
and various servers such as bridge servers, voicemail servers,
announcement servers, etc. Outside of the trust boundary lie the
customer premises equipment, and various media servers operated by
third-party service providers.
Certain subscriber-specific information, such as billing and
accounting information, stays within the trust boundary. Other
subscriber-specific information, such as endpoint identity, may be
presented to untrusted endpoints or may be withheld based on
subscriber profiles.
The SIP User Agent (UA) may be either within the trust boundary
(e.g. PSTN gateway) or outside the trust boundary (e.g. MTA),
depending on exactly what function is being performed and exactly
how it is being performed. Accordingly, the procedures followed by
a User Agent, as contained in the accompanying drafts, are different
depending on whether the UA is within the trust boundary or outside
the trust boundary. A trusted user agent is, in almost all cases,
equivalent to the combination of an untrusted user agent and a
proxy.
4.5 Basic Call Flow
Figure 2 presents a high-level overview of a basic MTA-to-MTA call
flow in DCS. Each MTA is associated with a DCS-proxy, which acts as
a SIP proxy. When a user goes off-hook and dials a telephone
number, the originating MTA (MTA-o) collects the dialed digits and
sends the initial INVITE message in SIP, to the "originating" DCS-
proxy (DP-o). This INVITE contains SDP proposing a set of codecs
that are acceptable to MTA-o (and their implied bandwidth
requirements), and an indication of the (mandatory) QoS
preconditions [9] needed for the session. DP-o verifies that MTA-o
is a valid subscriber of the telephony service (using authentication
DCS Group Category: Informational - Expiration 8/31/02 10
DCS Architecture February 2002
information in the INVITE message) and determines whether this
subscriber is authorized to place this call. DP-o then translates
the dialed number into the address of a "terminating" DCS-proxy (DP-
t) and forwards the INVITE message to it.
We assume that the originating and terminating DCS-proxies trust
each other. DP-o augments the INVITE message that it forwards with
additional information, such as billing information containing the
account number of the caller. DP-t then translates the dialed
number into the address of the terminating MTA (MTA-t) and forwards
the INVITE message to MTA to notify it about the incoming call.
The initial INVITE message invokes call feature handling at the
terminating MTA, such as call-forwarding. Assuming that the call is
not forwarded, MTA-t negotiates the coding style and bandwidth
requirements for the media streams. A reliable provisional 1xx
response to the initial INVITE is forwarded back through the DCS-
proxies.
DCS Group Category: Informational - Expiration 8/31/02 11
DCS Architecture February 2002
MTA-o ER-o DP-o DP-t ER-t MTA-t
| Invite | | | | |
|----------|--------->| Invite | | |
| | |--------->| | |
| | | | Invite | |
| | | |----------|--------->|
| | | | | 183 SDP |
| | | |<---------|----------|
| | | | | |
| | Gate | 183 SDP |Gate Setup| |
| | Setup |<---------|--------->| |
| |<---------| | | |
| 183 SDP | | | | |
|<---------|----------| | | |
| | | PRACK | | |
|----------|----------|----------|----------|--------->|
| | 200 OK (acknowledging PRACK) | |
|<---------|----------|----------|----------|----------|
| | | | | |
|<---------|--------Reserve Resources-------|--------->|
| | | | | |
| | COMET | |
|----------|--------- |----------|----------|--------->|
| 200 OK (acknowledging COMET) |
|<---------|----------|----------|----------|----------|
| | | | | 180 Ring |
| | | 180 Ring |<---------|----------|
| | 180 Ring |<---------| | |
|<---------|----------| | | |
| | | PRACK | | |
|----------|----------|----------|----------|--------->|
| | 200 OK (acknowledging PRACK) | |
|<---------|----------|----------|----------|----------|
| | | | | | User
| | | | | 200 OK | Answers
| | | 200 OK |<---------|----------|
| | 200 OK |<---------| | |
|<---------|----------| | | |
| ACK | | | | |
|----------|----------|----------|----------|--------->|
| | | | | |
|<---------|----------Active Call----------|--------->|
| | | | | | User
| | | | | BYE | Hangs Up
|<---------|----------|----------|----------|----------|
| | | | | 200 OK |
|----------|----------|----------|----------|--------->|
Figure 2: A Basic Call Flow, including Resource Management functions
DCS Group Category: Informational - Expiration 8/31/02 12
DCS Architecture February 2002
In the figure, MTA-t sends a 183 SDP message[8] to DP-t. The 183
SDP contains a subset of the capabilities in the INVITE message that
are acceptable to MTA-t. The SDP also carries the QoS preconditions
from the INVITE. DP-t sends a GATE-SETUP message to the terminating
ER (ER-t), conveying policy instructions allowing ER-t to open a
gate for the IP flow associated with this phone call. The GATE_SETUP
message contains billing information containing the account number
of the subscriber that will pay for the call.
DP-t forwards the 183 SDP to DP-o. DP-o sends a GATE-SETUP message
to the originating ER (ER-o) to indicate that it can open a gate for
the IP flow associated with the phone call. Finally, DP-o forwards
200 OK to MTA-o. The initial INVITE request and 183 SDP response
contain a SIP Contact header to indicate the IP address of the
remote MTA to be used for subsequent end-to-end SIP signaling
exchanges. MTA-o acknowledges the 183 SDP by sending a PRACK [7]
directly to MTA-t. The PRACK may contain the SDP to allow for a
further step in the negotiation of capabilities for the session.
Once the initial INVITE/183/PRACK exchange has completed, both MTAs
reserve the resources that will be needed for the media streams.
Once MTA-o has successfully made its reservation, it sends a COMET
message [9] to MTA-t, which is immediately acknowledged by MTA-t
with a 200-OK. MTA-o uses the COMET message to communicate the fact
that the desired pre-conditions necessary for the session as
perceived by MTA-o are satisfied (e.g., successful reservation of
resources, as perceived by MTA-o.) MTA-t acknowledges the COMET
message with a 200 OK final response directly to MTA-o. However,
resource reservation from MTA-t's perspective may not be completed
yet. Thus, the 200 OK acknowledging the COMET message does not
indicate successful resource reservation. Once MTA-t successfully
reserves the resources needed for the call, it sends a 180 Ringing
through the proxies to indicate that the phone is ringing, and that
the calling party should be given a ringback call progress tone. We
have not described, in detail, the messaging involved in resource
reservation here, as we believe that it is appropriate to allow for
a variety of resource management mechanisms. Thus, the MTA may use
the resource management mechanism that is most suitable to the
network segment that it is attached to. When the called party
answers, by going off-hook, MTA-t sends a 200 OK final response
through the proxies, which MTA-o acknowledges with an end-to-end
ACK. At this point the resources that were previously reserved are
committed to this conversation, and the call is "cut through."
Either party can terminate the call. An MTA that detects an on-hook
sends a SIP BYE message to the remote MTA, which is acknowledged.
5. Resource Management
DCS's resource management protocols distinguish between two phases:
a "Reserve" phase and a "Commit" phase. During the Reserve phase,
resources are reserved but are not yet made available to the
endpoint. This ensures that resources are available before ringing
DCS Group Category: Informational - Expiration 8/31/02 13
DCS Architecture February 2002
the far-end telephone. The Commit phase, which commits the
resources associated with the flow, is initiated after ringing the
far end telephone and after the called party picks up. At this
point, the resources are made available to the endpoint, and
recording is started so that the user can be billed for usage. The
use of a two-phase approach is essential because of the unique
requirements associated with human communication, such as telephony.
Recognition of the need for a two phase resource management approach
is a significant motivation for the call flow adopted in the
previous section.
Although we believe that issues of billing ought not to be the
primary consideration in the design of the protocol, the protocol
design should not preclude the possibility of usage sensitive
billing. Therefore, in addition to ensuring that resources are
available before ringing the phone, the two-phase resource
management protocol also allows us to preserve the semantics of
billing that users are accustomed to, whereby usage recording is not
started until the called party picks up the phone. Backbone
resources are reserved and allocated in the first phase of the two-
phase resource reservation protocol. This is important in order to
limit the impact of backbone resource management on post-pickup
delay (this minimizes the likelihood of clipping the first few
syllables of the conversation).
6. Distributed Call State
In order to provide enhanced services to millions of endpoints, we
need an architecture that can be implemented cost-effectively at
very large scale. Just as we enable flexibility by exploiting
intelligence at the endpoints, services can be provided in a
scaleable manner by storing the state associated with applications
at the endpoints, rather than in network servers. Especially with
telephony, endpoints are directly involved in handling calls and
therefore need to maintain and use call state. In contrast, while
network servers may need to be involved when setting up a call to
gain access to enhanced QoS, there is no fundamental need for those
servers to be involved throughout the lifetime of the call.
Maintaining state for every call at network servers, while
achievable, increases the reliability requirements and load on the
servers. The less state kept in the network, the better.
As a result, the DCS-proxies in DCS are designed to be Call
stateless transaction servers. The proxy maintains SIP transaction
state. So, when a DCS-proxy processes a service request from an
endpoint, it maintains state until the transaction is complete, but
does not maintain any per-call state about active calls in the
network. There are two major advantages to this design. First the
reliability of the service does not depend on the reliability of an
individual DCS-proxy. A DCS-proxy can fail without affecting calls
that are currently in progress. Second, it removes many complex
synchronization problems where two (or more) entities need to have
simultaneously accurate information. Since interactions with the
DCS Group Category: Informational - Expiration 8/31/02 14
DCS Architecture February 2002
DCS-proxies are simple stateless transactions, it is not necessary
for consecutive calls to be processed by the same DCS-proxy. DCS-
proxy crashes affect only the transient calls (the calls that are in
the process of being set up), and not stable conversations.
Further, it is likely that most calls in a transient state can be
recovered and successfully established through a backup or spare
DCS-proxy using endpoint retransmission, with no explicit
synchronization protocol required between the DCS-proxies. We
believe this design principle will enable us to operate in very
large scale, cost effectively. Furthermore it places the function
of managing the state of a call where it belongs - at the endpoint.
An existing call can only be affected by failures along the path or
by failure of the endpoints: there are no unnecessary elements
involved in a call.
We note that there are many services that involve the use of servers
or proxy endpoints that communicate directly with clients. Since
these endpoints are directly involved in providing service, it is
necessary and appropriate for them to maintain state. Examples of
proxy endpoints include application layer firewalls, caching
servers, transcoders, network-based conference bridges, interactive
voice response systems, and PSTN gateways. The DCS architecture
models these as end-points, that maintain appropriate call state.
We now turn to the mechanisms that allow us to avoid state in the
DCS-proxies. A number of examples of the need for distributed state
arise in the implementation of telephony features. These give rise
to two types of information that a DCS-proxy may present to an
endpoint that may subsequently be given back to the proxy by the
endpoint. The first type of information is Remote endpoint
identification, contained in the "Remote-Party-ID" header. The
second type of information is associated with an active session that
an endpoint is participating in. This latter information, stored in
the "State" header, is information that a service provider or proxy
may need for methods that are invoked by an endpoint related to that
session. Thus, a DCS-proxy stores the state information about the
calls at an endpoint in two new headers, "State" and "Remote-Party-
ID". The State header is both encrypted and signed by the proxy to
ensure the privacy and the integrity of the information contained in
the header. The information that may be contained in State includes
resource information (such as Gate information) and billing
information (such as a billing id). The Remote-Party-ID is only
encrypted when privacy is requested by the endpoint (covered in
detail in the Section 7 below.)
When needed, the endpoint provides the State to the DCS-proxy that
generated it, which can use the information to provide additional
functionality.
Because the State header is encrypted and signed by the DCS-proxy,
the information it contains is trusted by the network even though
the endpoint itself is not trusted. In addition, DCS-proxies store
service-specific opaque data associated with a call at the edge
DCS Group Category: Informational - Expiration 8/31/02 15
DCS Architecture February 2002
router. Since charging for telephony services may be tied to the
use of resources, this information is best stored at the edge
router, where knowledge of resource usage exists.
The endpoint returns the state (possibly both State and Remote-
Party-ID) information to the DCS-proxy when it is needed to
implement specific features. The endpoint cannot interpret the
information in the encrypted and signed State header (and Remote-
Party-ID if it is also encrypted), and any attempt to tamper with it
can be detected by the DCS-proxy.
An example of use of the State information is one where a change in
coding method in the middle of a call (e.g., upon detection of a fax
tone) may require the proxies to authorize additional resources.
Services such as call-transfer and three-way-calling require the
proxy to be involved in authorizing resources for packet flows to
the new destination(s).
7. DCS Proxy - DCS Proxy Communications
DCS-proxies implement a set of service-specific control functions
required to support the telephony service:
. Authentication and authorization: Since services are only provided
to authorized subscribers, DCS-proxies authenticate signaling
messages and authorize requests for service on a call-by-call
basis.
. Name/number translation and call routing: DCS-proxies translate
dialed E.164 numbers, or names, to a terminating IP address based
on call routing logic to support a wide range of call features.
. Service-specific admission control: DCS-proxies can implement a
broad range of admission control policies for the telephony
service. For example, DCS-proxies may provide precedence for
particular calls (e.g., 911 calls). Admission control may also be
used to implement overload control mechanisms, e.g. to restrict
the number of calls to a particular location or to restrict the
frequency of call setup to avoid signaling overload.
. Signaling and service feature support: While many service features
are implemented by endpoints, the DCS-proxy also plays a role in
feature support. DCS signaling provides a set of service
primitives to end-points that are mediated by the DCS-proxy. The
DCS-proxy is involved in implementing service features that depend
on the privacy of calling information, e.g., caller-ID blocking.
It also plays a role in supporting service features that require
users to receive a consistent view of feature operation even when
an endpoint is down. For example, while an endpoint may normally
participate in call forwarding, the DCS-proxy can control call
forwarding on behalf of an endpoint when the endpoint is down.
DCS Group Category: Informational - Expiration 8/31/02 16
DCS Architecture February 2002
End-points MTA-o and MTA-t communicate through the DCS-Proxies DP-o
and DP-t, as shown in Figure 2. The interface of concern in this
section is the one between the DCS-Proxies DP-o and DP-t. In
contrast to a true stateless SIP proxy, the DCS-Proxy maintains
transaction state. During the interval that a call is being setup, a
DCS-Proxy keeps state related to a request until a response is
received.
For each call made to a phone number, DP-o may need to perform the
functions needed for Local Number Portability (LNP). If a LNP
database lookup is performed and the resulting dialed string is
modified, DP-o must modify the Request-URI to include the result of
the LNP lookup. The originating proxy DP-o generates and stores the
State header. This information is intended to be sent to endpoint
MTA-o and included with the first response that is returned to MTA-
o. The originating DCS-Proxy, DP-o, may then use the call state
information provided to it in the State header to manipulate call-
legs when requested by MTA-o.
As with conventional SIP proxies, DP-o adds its address to the top
of the Via: header list with a branch=1 field when forwarding the
request. In addition, to support billing functions for a carrier,
DP-o appends opaque information called the Billing-Info and Billing-
ID. In addition, to support the resource management functions (such
as manipulating Gates for resource management in concert with call-
leg manipulation), a Gate-Location: header is included. This allows
for the subsequent generation of requests for access network QoS by
the end-points.
We also depend on originating DCS-Proxy, DP-o to be responsible for
manipulating call legs. For instance, when a call is being
forwarded, information about the new destination that the call is
being forwarded to is provided by DP-t to DP-o. The new INVITE is
then issued from DP-o. The information exchanged between the DCS-
proxies enables such a function to be performed.
8. Privacy
Many conventional telephony systems have the ability to provide
information about the identity of the calling party to the called
party before the latter accepts the call (such a capability is
typically termed "Caller-ID"). Systems that support Caller-ID
usually provide a mechanism that allows the calling party to
instruct the network to refrain from delivering this information to
the destination.
In order for an IP-based network to provide a caller with a similar
capability, a new SIP header is needed to signal the desire for
anonymity to the network elements that would otherwise provide the
caller's identity to the destination party. If a caller desires to
remain anonymous, several additional changes to standard SIP are
necessary.
DCS Group Category: Informational - Expiration 8/31/02 17
DCS Architecture February 2002
The triplet {From:, To:, Call-ID:} is used to identify a call leg in
both endpoints and in proxies. Because call state information is
pushed to the edge of the network, this information must be
delivered unchanged to the destination endpoint.
The SIP From: header normally contains information that identifies
the caller. In order to hide the identity of the caller, the From:
header information is encrypted with the originating endpoint's key.
The destination endpoint does not possess the key to decrypt the
From: information. No new syntax for SIP is introduced here.
Normally, the SIP Call-ID: header also contains information about
the caller. In the DCS architecture, to support privacy the value of
the Call-ID: header is a cryptographic hash string that contains no
information about the user.
Since all the normally available mechanisms for passing information
about the caller are no longer available, a new SIP header, Remote-
Party-ID, is used to pass the caller's identity to the destination.
The Remote-Party-ID header is primarily used for endpoint
identification. This header contains the information that would
normally be present in the From: header; the network passes it to
the destination endpoint only if the caller has not requested
anonymity. If the caller had requested anonymity, then the Remote-
Party-ID header contains an encrypted string that can be used by the
proxy in handling further requests.
If the user at an endpoint wants to return the last call (e.g., by
dialing *69 on a traditional telephone) the "call return" function
is invoked. If the user had subscribed to the caller ID service
feature, the terminating endpoint could store the information (phone
number or IP address) associated with the last call. However, it
may be the case that the user does not subscribe to the feature, or
the originator of the previous call may have requested that this
information be blocked in order to retain privacy. In this case,
call return can be implemented, while keeping the caller's identity
private, by using the encrypted Remote-Party-ID header.
In addition to the usual privacy elements provided by telephone
systems, IP-based systems must implement methods of hiding the
source IP address from the destination if the caller requires
privacy. The entire address must be obscured, since even a few
address bits may provide partial location information. Likewise, IP
addresses of the destination should not be revealed to the caller,
in order to maintain privacy of transfer destinations.
IP addresses typically appear in the Contact: header; they also
appear in SDP descriptions contained in SIP messages. These must all
be protected. We chose to use an application-level anonymizer that
inspects the SIP call signaling messages and replaces any
identifying information contained therein in a consistent manner.
The identifying information is modified such that when the messages
DCS Group Category: Informational - Expiration 8/31/02 18
DCS Architecture February 2002
are delivered to the destination endpoint any identifying
information has been replaced with fields that obscure the identity
of the party seeking privacy.
This mechanism does not require any modification to the call
signaling initiated by the endpoints: the application-level
anonymizer performs these functions silently within the network.
9. Security Considerations
Detailed security considerations related to this architecture will
be addressed in a future companion draft.
10. Call Flows
This section contains sample message flows between MTAs, DCS-
Proxies, and Call Management Systems (CMSs, which are trusted User
Agents, as described in section 3.4).
The first four subsections provide details for handling of basic
calls, between all combinations of MTAs and CMSs.
Following subsections provide details of the handling of call
features, such as call-forwarding, call-transfer, three-way-calling,
CODEC changes, operator services, electronic surveillance, and IP
address privacy.
DCS Group Category: Informational - Expiration 8/31/02 19
DCS Architecture February 2002
10.1 Basic Call Flow from MTA to MTA
MTA-o ER-o Proxy-o Proxy-t ER-t MTA-t
| (1)Invite | | | |
|----------|--------->|(2)Invite | | |
| | |--------->| | |
| | | |(3)Invite | |
| | | |----------|--------->|
| | | | |(4)183 SDP|
| | | |<---------|----------|
| | | | | |
| | Gate |(5)183 SDP|Gate Setup| |
| | Setup |<---------|--------->| |
| |<---------| | | |
| (6)183 SDP | | | |
|<---------|----------| | | |
| | |(7)PRACK | | |
|----------|----------|----------|----------|--------->|
| |(8)200 OK (acknowledging PRACK) | |
|<---------|----------|----------|----------|----------|
| | | | | |
|<---------|--------Reserve Resources-------|--------->|
| | | | | |
| | (9)COMET | |
|----------|--------- |----------|----------|--------->|
| (10)200 OK (acknowledging COMET) |
|<---------|----------|----------|----------|----------|
| | | | (11)180 Ring |
| | | (12)180 |<---------|----------|
| (13)180 Ring |<---------| | |
|<---------|----------| | | |
| | |(14)PRACK | | |
|----------|----------|----------|----------|--------->|
| | (15)200 OK (acknowledging PRACK) |
|<---------|----------|----------|----------|----------|
| | | | | | User
| | | | (16)200 OK | Answers
| | | (17)200 |<---------|----------|
| (18)200 OK |<---------| | |
|<---------|----------| | | |
| (19)ACK | | | |
|----------|----------|----------|----------|--------->|
| | | | | |
|<---------|----------Active Call----------|--------->|
| | | | | | User
| | | | (20)BYE | Hangs Up
|<---------|----------|----------|----------|----------|
| | | | (21)200 OK |
|----------|----------|----------|----------|--------->|
DCS Group Category: Informational - Expiration 8/31/02 20
DCS Architecture February 2002
The above figure shows the basic DCS call flow from one MTA to
another. The basic DCS call flow starts with an INVITE from MTA-o
to MTA-t through proxies Proxy-o and Proxy-t. It follows the
conventions of SIP. The Via headers are used to track the path of
the request (INVITE) so that the response can traverse backwards
through the same path.
This INVITE is sent requesting that MTA-t not ring until the QoS
preconditions are met. The purpose of this first INVITE is to
invoke call features, such as call forwarding, to determine the
proper destination MTA, and to negotiate the bandwidth and codec to
be used so that the proper resources can be reserved. The response
(183-Session-Progress) acknowledges the receipt of the INVITE
message, provides the SDP for the forward media flow, and provides
contact information for end-to-end messages that happen later in the
call flow. When the INVITE is received, MTA-t's state reflects that
a call is now being set-up. After MTA-o receives the 183-Session-
Progress, it sends a PRACK message directly to MTA-t (as specified
in the contact header) to acknowledgement receipt of MTA-t's SDP.
After resources are reserved for the call, a COMET is sent to MTA-t.
MTA-t responds with a 200-OK, and also sends a ringback indication
in the form of a 180-Ringing message. When the call is answered, a
200-OK to the INVITE is sent back to MTA-o, which ACKs the OK to
MTA-t to complete the triple handshake.
The bearer channel session can now be established. When the call is
over, either end can send a BYE message directly to the other end.
This BYE request must also be responded to with a 200-OK.
The detailed steps followed and messages exchanged are:
A call setup begins when MTA-o detects off-hook on one of its lines.
MTA-o first puts that line in the "busy" state. MTA-o sends an
audible dialtone signal to the customer and begins to detect DTMF
digits. Upon receiving the first digit, MTA-o stops dialtone.
Once a complete E.164 number has been received (based upon a digit
map that has been provisioned in the MTA), MTA-o generates the
following INVITE message and sends it to Proxy-o (the DCS-proxy that
manages MTA-o). MTA-o starts the retransmission timer (T-proxy-
request).
(1) INVITE
INVITE sip:555-2222@Host(DP-o);user=phone SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
Remote-Party-ID: John Doe <tel:555-1111>
Anonymity: Off
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
DCS Group Category: Informational - Expiration 8/31/02 21
DCS Architecture February 2002
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuite:312F
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
The Request-URI starts with the dialed number from the user. The
Remote-Party-ID gives the calling name and number, as provided by
the MTA. Even though Anonymity indicates calling name and number
privacy is not required for this call, the From, To, and Call-ID
headers contain cryptographically random values to maintain privacy
of the caller.
Upon receiving the INVITE message, Proxy-o authenticates MTA-o using
standard IPSec authentication. Proxy-o examines the Remote-Party-ID:
line and checks to see that this originating phone number belongs to
MTA-o, and is authorized for originating service. Proxy-o also
checks to make sure the calling name in the Remote-Party-ID: line is
a valid calling name for this line. Proxy-o then sends the dialed
number to a directory server for resolution to an IP address. In
this example, the directory server returns the address of Proxy-t,
the Proxy that manages the terminating MTA. Proxy-o generates the
following INVITE message and sends it to Proxy-t. Proxy-oadds a
number of parameters to the INVITE message, which are described
below. Upon sending this INVITE message, Proxy-o starts the
retransmisison timer (T-proxy-request) and starts the T3 session
timer (T-proxy-setup). The retransmission timer is cancelled on
receipt of the optional 100-Trying provisional response (not present
in this call flow); both are cancelled on receipt of the 183-
Session-Progress provisional response.
(2) INVITE
INVITE sip:+1-212-555-2222;rn=+1-212-234-2222;
npdi=yes@Host(dp-t);user=phone SIP/2.0
Via: SIP/2.0/UDP Host(DP-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
Require: state
Proxy-Require: dcs, state
DCS Group Category: Informational - Expiration 8/31/02 22
DCS Architecture February 2002
Remote-Party-ID: John Doe; <tel:+1-212-555-1111>
Anonymity: Off
Dcs-Gate: Host(cmts-o.provider):3612/17S30124/37FA1948 required
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/
212-555-1111/212-555-2222>
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124;
orig-dest=tel:+1-212-555-2222; num-redirects=0
Dcs-Billing-ID: Host(dp-o.provider):36123E5C:0152
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
The "lrn" in the Request-URI shows that LNP dip has been done, and
gives the result. The dialed number is fully expanded into E.164
number. The Remote-Party-ID header contains verified Calling-Name
and full E.164 Calling-Number. Dcs-Gate contains the IP address of
the CMTS, the identity of the originating gate, and key for gate
coordination messages. Also contained is the indication that gate
coordination is required for this call. Dcs-Billing-Info contains
the IP address of the record-keeping-server for event collection,
the account number, originating number, and terminating number for
billing of this call. State contains the state information wanted
by Proxy-o for handling of messages from MTA-t to MTA-o. Dcs-
Billing-ID contains the unique Billing identifier, made up of the
CMS IP address, timestamp, and sequence number. A suggested
encryption key is inserted into the SDP.
Upon receiving this INVITE message, Proxy-t authenticates that the
sender was Proxy-o using IPSec, and sends the E.164-t address to the
directory server. In this example, the Directory Server is able to
translate E.164-t to the IP address of MTA-t (one of the MTAs
managed by Proxy-t). Proxy-t then checks to see if MTA-t is
authorized for receiving this call. Proxy-talso checks the account
DCS Group Category: Informational - Expiration 8/31/02 23
DCS Architecture February 2002
information to determine if MTA-o is paying for the call or if MTA-t
is expected to pay. Proxy-t generates the following INVITE message
and sends it to MTA-t. The Remote-Party-ID line appears unchanged
only if the destination MTA has subscribed to caller-id service;
otherwise, or if the caller had specified privacy of the caller
information, the Remote-Party-ID line would be altered. Note that
the Via lines have been encrypted, maintaining the privacy of the
caller. The line State has been added, and contains all the
information needed by the Proxy for any subsequent call features
that may be requested. This information is signed by Proxy-t and
encrypted.
Upon sending this INVITE message, Proxy-t starts the retransmisison
timer (T-proxy-request) and starts the T3 session timer (T-proxy-
setup). The retransmission timer is cancelled on receipt of the
optional 100-Trying provisional response (not present in this call
flow); both are cancelled on receipt of the 183-Session-Progress
provisional response.
(3) INVITE
INVITE sip:555-2222@Host(mta-t.provider); user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
Supported: 100rel, state
Require: state
Remote-Party-ID: John Doe; <tel:+1-212-555-1111>
Media-Authorization: 31S14621
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
DCS Group Category: Informational - Expiration 8/31/02 24
DCS Architecture February 2002
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Local number portability information has been removed from the
Request-URI, and the username is a string that is known to MTA-t.
Via headers are encrypted to provide calling party privacy. Media-
Authorization header contains the Gate-ID at the CMTS controlling
the resources for MTA-t. State contains a string encrypted with a
Proxy-t privately-held key, and contains nexthop routing
information, CMTS address, Gate-ID, and all previous state headers
from other proxies.
Upon receiving this INVITE, MTA-t authenticates that the message
came from Proxy-t using IPSec. MTA-t checks the telephone line
associated with the E.164-t (as found in the Request URI) to see if
it is available. If it is available, MTA-t looks at the capability
parameters in the Session Description Protocol (SDP) part of the
message and determines which media channel parameters it can
accommodate for this call. MTA-t stores the INVITE message,
including the encrypted State parameters, for later use. MTA-t
puts this line in the "busy" state (so any other call attempts are
rejected until this call clears), generates the following 183-
Session-Progress response, and sends it to Proxy-t. MTA-t starts
the retransmission timer with value (T-proxy-response) and starts
the session timer (T3) with value (T-resource).
MTA-t can, at its option, still accept further incoming calls and
present them all to the customer. Such enhanced user interfaces for
the MTA is beyond the scope of this specification. Note that MTA-t
can't use the To: header field to determine the proper line, as it
may be totally unrelated to the phone number at MTA-t.
(4)183-Session-Progress
SIP/2.0 183 Session Progress
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
Require: 100rel
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
Remote-Party-ID: John Smith <tel:555-2222>
Anonymity: off
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Rseq: 9021
Content-Disposition: precondition
Contact: sip:Host(mta-t.provider)
DCS Group Category: Informational - Expiration 8/31/02 25
DCS Architecture February 2002
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-t.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=rtpmap:0 PCMU/8000
m=audio 6544 RTP/AVP 0
a=qos:mandatory sendrecv confirm
Remote-Party-ID contains the called name and number, as provided by
MTA. Anonymity indicates called name and number privacy is not
requested for this call. SDP contains MTA-t's bearer channel IP
address, and negotiated voice encoding parameters.
Upon receiving the 183-Session-Progress message, Proxy-t forwards
the following message to Proxy-o, restoring the Via headers, and
adding Dcs-Gate information. At this point Proxy-t has completed
all the call processing functions needed for this call, deletes its
local state information, and handles all remaining messages as a
stateless proxy. Proxy-t may include Dcs-Billing-Information if it
wishes to override the billing information that came in the INVITE
(e.g. collect or toll-free call).
(5) 183-Session-Progress:
SIP/2.0 183 Session Progress
Via: SIP/2.0/UDP Host(dp-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
Require: 100rel, state
Proxy-Require: dcs, state
State: Host(dp-t.provider); nexthop=sip:555-2222@Host(mta-
t.provider); gate=Host(cmts-t.provider):4321/31S14621;
orig-dest=tel:+1-212-555-1111; num-redirects=0
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124;
orig-dest=tel:+1-212-555-2222; num-redirects=0
Dcs-Gate: Host(cmts-t.provider):4321/31S14621/37FA1948
Remote-Party-ID: John Smith <tel:+1-212-555-2222>
Anonymity: off
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Rseq: 9021
Content-Disposition: precondition
Contact: sip:Host(mta-t.provider)
Content-Type: application/sdp
DCS Group Category: Informational - Expiration 8/31/02 26
DCS Architecture February 2002
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-t.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=rtpmap:0 PCMU/8000
m=audio 6544 RTP/AVP 0
a=qos:mandatory sendrecv confirm
Upon receiving the 183-Session-Progress message, Proxy-o forwards
the following message to MTA-o. This message contains a State
parameter giving all the information needed by the Proxy for later
features. The State value is signed by Proxy-o and encrypted by
Proxy-o's privately-held key. At this point Proxy-o has completed
all the call processing functions needed for this call, deletes its
local state information, and handles all remaining messages as a
stateless proxy.
(6) 183-Session-Progress:
SIP/2.0 183 Session Progress
Via: Sip/2.0/UDP Host(mta-o.provider)
Require: 100rel, state
Media-Authorization: 17S30124
State: Host(dp-o.provider); state="{gate= Host(cmts-
o.provider): 3612/17S30124, nexthop=sip:+1-212-555-
2222;rn=+1-212-2342222;npdi=yes@Host(DP-t),
state="Host(dp- t.provider);
nexthop=sip:555-2222@Host(mta-t.provider);
gate=Host(cmts-t.provider):4321/31S14621; orig-
dest=tel:+1-212-555-1111; num-redirects=0"}K"
Remote-Party-ID: John Smith <tel:+1-212-555-2222>
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Rseq: 9021
Content-Disposition: precondition
Contact: sip:Host(mta-t.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
DCS Group Category: Informational - Expiration 8/31/02 27
DCS Architecture February 2002
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 6544 RTP/AVP 0
a=qos:mandatory sendrecv confirm
Upon receiving the 183-Session-Progress message, MTA-o stops timer
(T-proxy-request) and sends the following PRACK message directly to
MTA-t using the IP address in the Contact header of the 183-Session-
Progress message.
(7) PRACK:
PRACK sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 128 PRACK
Rack: 9021 127 INVITE
Content-Type: application/sdp
Content-length: (.)
v=0
O=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
MTA-t acknowledges the PRACK with a 200-OK, and begins to reserve
the resources necessary for the call.
(8) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 128 PRACK
After sending PRACK(7), MTA-o attempts to reserve network resources
if necessary. If resource reservation is successful, MTA-o sends
the following COMET message directly to MTA-t. MTA-o starts timer
(T-direct-request).
DCS Group Category: Informational - Expiration 8/31/02 28
DCS Architecture February 2002
(9) COMET:
COMET sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 COMET
Content-Type: application/sdp
Content-length: (.)
v=0
O=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 3456 RTP/AVP 0
a=qos:success send
MTA-t acknowledges the COMET message with a 200-OK.
(10) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 COMET
Upon receipt of the 200-OK(10), MTA-o stops timer (T-direct-
request).
Upon receipt of the (7) PRACK message, MTA-t stops timer (T-proxy-
response) and attempts to reserve network resources if necessary.
Once MTA-t both receives the COMET message and has successfully
reserved network resources, MTA-t begins to send ringing voltage to
the designated line and sends the following 180 RINGING message
through Proxy-t. MTA-t restarts the session timer (T3) with value
(T-ringing).
(11) 180 RINGING:
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)} K
Require: 100rel
DCS Group Category: Informational - Expiration 8/31/02 29
DCS Architecture February 2002
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Contact: sip:Host(mta-t.provider)
Cseq: 127 INVITE
Rseq: 9022
Proxy-t decodes the Via: headers, and passes the 180-Ringing to
Proxy-o. This operation is done as a SIP stateless proxy.
(12) 180 RINGING:
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP Host(dp-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
Require: 100rel
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Rseq: 9022
Proxy-o handles the message as a SIP stateless proxy, and passes the
180-Ringing to MTA-o.
(13) 180 RINGING:
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP Host(mta-o.provider)
Require: 100rel
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Rseq: 9022
Upon receipt of the 180 RINGING message, MTA-o restarts the
transaction timer (T3) with value (T-ringing). MTA-o acknowledges
the provisional response with a PRACK, and plays audible ringback
tone to the customer.
DCS Group Category: Informational - Expiration 8/31/02 30
DCS Architecture February 2002
(14) PRACK:
PRACK sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Contact: sip:Host(mta-t.provider)
Cseq: 130 PRACK
Rseq: 9022 127 INVITE
MTA-t acknowledges the PRACK with a 200-OK, and stops timer (T-
proxy-response).
(15) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 130 PRACK
Once MTA-t detects off-hook on the called line, it disconnects
ringing voltage from the line and sends the final response through
the proxies. MTA-t stops timer (T-ringing) and starts timer (T-
proxy-response). If necessary, MTA-t may also commit to resources
that have been reserved for this call. At this point, MTA-t begins
to generate bearer channel packets of encoded voice and send them to
MTA-o using the IP address and port number specified in the SDP part
of the original INVITE message.
(16) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)} K
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Proxy-t handles the message as a SIP stateless proxy, and forwards
it to Proxy-o.
DCS Group Category: Informational - Expiration 8/31/02 31
DCS Architecture February 2002
(17) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(dp-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Proxy-o handles the message as a SIP stateless proxy, and forwards
it to MTA-o.
(18) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Upon receipt of the 200-OK message, MTA-o stops timer (T-ringing)
and stops playing audible ringback tone to the customer and begins
to play the bearer channel stream that is received from MTA-t. MTA-
o sends the following ACK message to MTA-t. If necessary, MTA-o may
also commit to resources that have been reserved for this call. At
this point, MTA-o begins to generate bearer channel packets of
encoded voice and send them to MTA-t using the IP address and port
number specified in the SDP part of the original 183-Session-
Progress message (that was a response to the original INVITE).
(19) ACK:
ACK sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 ACK
Upon receipt of the ACK message, MTA-t stop timer (T-proxy-
response).
When either MTA detects hangup, it sends out a BYE message to the
other MTA. In this example, MTA-o detected that the customer hung
up the phone. MTA-o puts that line in the "idle" state so new calls
can be made or received. It sends the following BYE message
directly to MTA-t. MTA-o may also need to release network resources
DCS Group Category: Informational - Expiration 8/31/02 32
DCS Architecture February 2002
that have been used for the call. MTA-o starts timer (T-direct-
request).
(20) BYE:
BYE sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 131 BYE
Upon receipt of the BYE message, MTA-t stops playing the bearer
channel stream received from MTA-o and, if necessary, releases
network resources that have been used for this call. MTA-tsends the
following 200-OK message to MTA-o. MTA-t starts a 15-second timer
(T-hangup) (Note: this is a local interface issue, and not part of
this specification). If MTA-t does not detect hangup on the line
before timer (T-hangup) expires, it plays "reorder" tone on the
customer line. Once hangup is detected, MTA-t puts that line in the
"idle" state so new calls can be made or received.
(21) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 131 BYE
Upon receipt of 200-OK, MTA-o stops timer (T-direct-request).
DCS Group Category: Informational - Expiration 8/31/02 33
DCS Architecture February 2002
10.2 Basic Call Flow from MTA to CMS
MTA-o Proxy-o CMS-t Endpoint-t
| (1)Invite | | |
|-------------------->|(2)Invite | |
| |--------->| |
| | | Private Signaling |
| | |<------------------->|
| |(3)183 SDP| |
| |<---------| |
| | | |
| (4)183 SDP | | |
|<--------------------| | |
| (5)PRACK | |
|---------------------|--------->| |
| | | Private Signaling |
| | |<------------------->|
| (6)200 OK (acknowledging PRACK)| |
|<--------------------|----------| |
| | | |
|<------------------Reserve Resources----------------->|
| | | |
| (7)COMET | |
|-------------------- |--------->| |
|(8)200 OK (acknowledging COMET) |
|<--------------------|----------| |
| | | Private Signaling |
| | |<------------------->|
| | (9)180 | |
| (10)180 Ringing |<---------| |
|<--------------------| | |
| (11)PRACK | |
|---------------------|--------->| |
|(12)200 OK (acknowledging PRACK) |
|<--------------------|----------| |
| | | | User
| | | Private Signaling | Answers
| | |<------------------->|
| | (13)200 | |
| (14)200 OK |<---------| |
|<--------------------| | |
| (15)ACK | | |
|---------------------|--------->| |
| | | |
|<--------------------Active Call-------------------->|
| | | | User
| | | Private Signaling | Hangs Up
| (16)BYE |<------------------->|
|<--------------------|----------| |
| (17)200 OK | |
|---------------------|--------->| |
DCS Group Category: Informational - Expiration 8/31/02 34
DCS Architecture February 2002
This section describes the DCS call signaling flow for a basic call
that terminate on the PSTN, or some other endpoint controlled by a
CMS.
A call setup begins when MTA-o detects off-hook on one of its lines.
MTA-o first puts that line in the "busy" state. MTA-o sends an
audible dialtone signal to the customer and begins to detect DTMF
digits. Upon receiving the first digit, MTA-o stops dialtone. Once
a complete E.164 number has been received (based upon a digit map
that has been provisioned in the MTA), MTA-o generates the following
SIP INVITE message and sends it to Proxy-o (the Proxy that manages
MTA-o). MTA-o starts the retransmission timer (T-proxy-request).
(1) INVITE:
INVITE sip:555-2222@Host(DP-o);user=phone SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
Remote-Party-ID: John Doe <tel:555-1111>
Anonymity: Off
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuite:312F
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Upon receiving the INVITE message, Proxy-o authenticates MTA-o using
standard IPSec authentication. Proxy-o examines the Remote-Party-ID:
line and checks to see that this originating phone number belongs to
MTA-o, and is authorized for originating service. Proxy-o also
checks to make sure the calling name in the Remote-Party-ID: line is
a valid calling name for this line. Proxy-o then sends the dialed
number to a directory server for resolution to an IP address. In
this example, the directory server returns the address of CMS-t, the
DCS Group Category: Informational - Expiration 8/31/02 35
DCS Architecture February 2002
CMS that manages the endpoint device. Proxy-o generates the
following INVITE message and sends it to CMS-t. Proxy-oadds a number
of parameters to the INVITE message, which are described below. Upon
sending this INVITE message, Proxy-o starts the retransmisison timer
(T-proxy-request) and starts the T3 session timer (T-proxy-setup).
The retransmission timer is cancelled on receipt of the optional
100-Trying provisional response (not present in this call flow);
both are cancelled on receipt of the 183-Session-Progress
provisional response.
(2) INVITE:
INVITE sip:+1-212-555-2222;rn=+1-212-234-2222;
npdi=yes@Host(cms-t);user=phone SIP/2.0
Via: SIP/2.0/UDP Host(DP-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
Require: state
Proxy-Require: dcs, state
Remote-Party-ID: John Doe; <tel:+1-212-555-1111>
Anonymity: Off
Dcs-Gate: Host(cmts-o.provider):3612/17S30124/37FA1948 required
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/212-
555-1111/212-555-2222>
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124;
orig-dest=tel:+1-212-555-2222; num-redirects=0
Dcs-Billing-ID: Host(dp-o.provider):36123E5C:0152
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Upon receiving this INVITE message, CMS-t authenticates that the
sender was Proxy-o using IPSec, and determines the proper endpoint
device to receive this call. CMS-t engages in local signaling with
DCS Group Category: Informational - Expiration 8/31/02 36
DCS Architecture February 2002
that endpoint device, outside the scope of this specification, and
determines the proper SDP for the media flow to this endpoint
device. When complete, CMS-t forwards the following message message
to Proxy-o. The CMS-t lists itself as the location of the Dcs-Gate,
since it simulates the gate operation. CMS-t may include Dcs-
Billing-Information if it wishes to override the billing information
that came in the INVITE (e.g. collect or toll-free call).
(3) 183-Session-Progress:
SIP/2.0 183 Session Progress
Via: SIP/2.0/UDP Host(dp-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
Require: 100rel, state
Proxy-Require: dcs, state
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124;
orig-dest=tel:+1-212-555-2222; num-redirects=0
Dcs-Gate: Host(cms-t.provider):4321/137S90721/805628
Remote-Party-ID: John Smith <tel:+1-212-555-2222>
Anonymity: off
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Rseq: 9021
Content-Disposition: precondition
Contact: sip:Host(cms-t.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mg02.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=rtpmap:0 PCMU/8000
m=audio 6544 RTP/AVP 0
a=qos:mandatory sendrecv confirm
Upon receiving the 183-Session-Progress message, Proxy-o forwards
the following message to MTA-o. This message contains a State
parameter giving all the information needed by the Proxy for later
features. The State value is signed by Proxy-o and encrypted by
Proxy-o's privately-held key. At this point Proxy-o has completed
all the call processing functions needed for this call, deletes its
local state information, and handles all remaining messages as a
stateless proxy.
(4) 183-Session-Progress:
SIP/2.0 183 Session Progress
DCS Group Category: Informational - Expiration 8/31/02 37
DCS Architecture February 2002
Via: Sip/2.0/UDP Host(mta-o.provider)
Require: 100rel, state
Media-Authorization: 17S30124
State: Host(dp-o.provider); state="{gate= Host(cmts-
o.provider): 3612/17S30124, nexthop=sip:+1-212-555-
2222;rn=+1-212-234-2222;npdi=yes@Host(cms-t)}K"
Remote-Party-ID: John Smith <tel:+1-212-555-2222>
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Rseq: 9021
Content-Disposition: precondition
Contact: sip:Host(cms-t.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mg02.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 6544 RTP/AVP 0
a-X=pc-qos:mandatory sendrecv confirm
Upon receiving the 183-Session-Progress message, MTA-o stops timer
(T-proxy-request) and sends the following PRACK message directly to
CMS-t using the IP address in the Contact header of the 183-Session-
Progress message.
(5) PRACK:
PRACK sip:Host(cms-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 128 PRACK
Rack: 9021 127 INVITE
Content-Type: application/sdp
Content-length: (.)
v=0
O=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
DCS Group Category: Informational - Expiration 8/31/02 38
DCS Architecture February 2002
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 3456 RTP/AVP 0
a-Qos:mandatory sendrecv
CMS-t acknowledges the PRACK with a 200-OK, and performs local
signaling with the endpoint (outside the scope of this
specification) in order to begin reserving the resources necessary
for the call.
(6) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 128 PRACK
After sending PRACK(5), MTA-o attempts to reserve network resources
if necessary. If resource reservation is successful, MTA-o sends
the following COMET message directly to CMS-t. MTA-o starts timer
(T-direct-request).
(7) COMET:
COMET sip:Host(cms-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 COMET
Content-Type: application/sdp
Content-length: (.)
v=0
O=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 3456 RTP/AVP 0
a=qos:success send
CMS-t acknowledges the COMET message with a 200-OK.
(8) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-o.provider)
DCS Group Category: Informational - Expiration 8/31/02 39
DCS Architecture February 2002
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 COMET
Upon receipt of the 200-OK(8), MTA-o stops timer (T-direct-request).
Upon receipt of the (5) PRACK message, CMS-t stops timer (T-proxy-
response) and signals the endpoint device to attempt to reserve the
network resources necessary. Once CMS-t both receives the COMET
message and acknowledgement from the endpoint device, CMS-t sends
the following 180-Ringing (or 183-Sesison-Progress, with a
Session:Media header) message. CMS-t restarts the session timer(T3)
with value (T-ringing).
(9) 180 RINGING:
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP Host(dp-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
Require: 100rel
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Contact: sip:Host(cms-t.provider)
Cseq: 127 INVITE
Rseq: 9022
Proxy-o handles the message as a SIP stateless proxy, and passes the
180-Ringing (or 183-Session-Progress) to MTA-o.
(10) 180 RINGING:
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP Host(mta-o.provider)
Require: 100rel
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Contact: sip:Host(cms-t.provider)
Cseq: 127 INVITE
RSeq: 9022
Upon receipt of the 180 RINGING message, MTA-o restarts the
transaction timer (T3) with value (T-ringing). MTA-o acknowledges
the provisional response with a PRACK, and plays audible ringback
tone to the customer.
(11) PRACK:
PRACK sip:Host(cms-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
DCS Group Category: Informational - Expiration 8/31/02 40
DCS Architecture February 2002
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 130 PRACK
RAck: 9022 127 INVITE
CMS-t acknowledges the PRACK with a 200-OK, and stops timer (T-
proxy-response).
(12) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 130 PRACK
Once CMS-t, via private signaling with the endpoint device, detects
off-hook on the called line, it sends the final response to the
INVITE. CMS-t stops timer (T-ringing) and starts timer (T-proxy-
response). If necessary, MTA-t may also commit to resources that
have been reserved for this call. At this point, the endpoint
device begins to generate bearer channel packets of encoded voice
and send them to MTA-o using the IP address and port number
specified in the SDP part of the original INVITE message.
(13) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(dp-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Proxy-o handles the message as a SIP stateless proxy, and forwards
it to MTA-o.
(14) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
DCS Group Category: Informational - Expiration 8/31/02 41
DCS Architecture February 2002
Upon receipt of the 200-OK message, MTA-o stops timer (T-ringing)
and stops playing audible ringback tone to the customer and begins
to play the bearer channel stream that is received. MTA-o sends the
following ACK message to CMS-t. If necessary, MTA-o may also commit
to resources that have been reserved for this call. At this point,
MTA-o begins to generate bearer channel packets of encoded voice and
send them to the remote endpoint using the IP address and port
number specified in the SDP part of the original 183-Session-
Progress message (that was a response to the original INVITE).
(15) ACK:
ACK sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 ACK
Upon receipt of the ACK message, CMS-t stop timer (T-proxy-
response).
When MTA-o detects a hangup, or the endpoint device controlled by
CMS-t detects a hangup, it sends out a BYE message to the other
endpoint. In this example, CMS-t detected that the customer hung up
the phone. CMS-t puts that line in the "idle" state so new calls can
be made or received. It sends the following BYE message directly to
MTA-o. CMS-t may also need to release network resources that have
been used for the call. CMS-t starts timer (T-direct-request).
(16) BYE:
BYE sip:Host(mta-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(cms-t.provider)
From: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
To: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 131 BYE
Upon receipt of the BYE message, MTA-o stops playing the bearer
channel stream received from the endpoint device, and, if necessary,
releases network resources that have been used for this call. MTA-o
sends the following 200-OK message to CMS-t. MTA-o starts a 15-
second timer (T-hangup) (Note: this is a local interface issue, and
not part of this specification). If MTA-o does not detect hangup on
the line before timer (T-hangup) expires, it plays "reorder" tone on
the customer line. Once hangup is detected, MTA-o puts that line in
the "idle" state so new calls can be made or received.
(17) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(cms-t.provider)
From: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
DCS Group Category: Informational - Expiration 8/31/02 42
DCS Architecture February 2002
To: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 131 BYE
Upon receipt of 200-OK, CMS-t stops timer (T-direct-request).
10.3 Basic Call Flow from CMS to MTA
Endpoint-o CMS-o Proxy-t MTA-t
| Private Signaling | | |
|<------------------->|(1)INVITE | |
| |--------->| (2)INVITE |
| | |-------------------->|
| | | (3) 183 SDP |
| | |<--------------------|
| |(4)183 SDP| |
| |<---------| |
| Private Signaling | | |
|<------------------->| | (5)PRACK |
| |------------------------------->|
| | (6)200 OK (acknowledging PRACK)|
| |<-------------------------------|
| | | |
|<------------------Reserve Resources----------------->|
| | | |
| Private Signaling | | |
|<------------------->| (7)COMET |
| |------------------------------->|
| |(8)200 OK (acknowledging COMET) |
| |<--------------------|----------|
| | | (9) 180 Ringing |
| | |<------------------->|
| | (10)180 | |
| Private Signaling |<---------| |
|<------------------->| (11)PRACK |
| |------------------------------->|
| |(12)200 OK (acknowledging PRACK)|
| |<-------------------------------|
| | | | User
| | | (13)200 OK | Answers
| | |<--------------------|
| | (14)200 | |
| Private Signaling |<---------| |
|<------------------->| (15)ACK |
| |------------------------------->|
| | | |
|<--------------------Active Call-------------------->|
| | | | User
| | (16)BYE | Hangs Up
| |<-------------------------------|
DCS Group Category: Informational - Expiration 8/31/02 43
DCS Architecture February 2002
| | (17)200 OK |
| |------------------------------->|
This example shows a call originating on the PSTN and directed to a
destination on the PacketCable network. We assume the same sequence
of user behavior as in the basic call flow of section 10.1, only
difference being the location of the originator.
A call setup begins when the endpoint device controlled by CMS-o
detects an off-hook condition on one of its lines. This event is
communicated to CMS-o through a private signaling exchange beyond
the scope of this specification. CMS-o first puts that line in the
"busy" state, and collects a complete E.164 number. As a result of a
translation function performed by CMS-o, the destination is
determined to be a DCS device served by Proxy-t. CMS-o generates
the following SIP INVITE message and sends it to Proxy-t. CMS-o
starts the retransmission timer (T-proxy-request) and starts the T3
session timer (T -setup). The retransmission timer is cancelled on
receipt of the optional 100-Trying provisional response (not present
in this call flow); both are cancelled on receipt of the 183-
Session-Progress provisional response.
(1) INVITE:
INVITE sip:+1-212-555-2222;rn=+1-212-234-2222;
npdi=yes@Host(DP-t);user=phone SIP/2.0
Via: SIP/2.0/UDP Host(cms-o.provider);branch=1
Supported: 100rel, state
Require: state
Proxy-Require: dcs, state
Remote-Party-ID: John Doe; <tel:+1-212-555-1111>
Anonymity: Off
Dcs-Gate: Host(cms-o.provider):3612/17S30124/37FA1948 optional
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/212-
555-1111/212-555-2222>
Dcs-Billing-ID: Host(cms-o.provider):36123E5C:0152
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:Host(cms-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mg02.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
DCS Group Category: Informational - Expiration 8/31/02 44
DCS Architecture February 2002
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Upon receiving this INVITE message, Proxy-t authenticates that the
sender was CMS-o using IPSec, and sends the E.164-t address to the
directory server. In this example, the Directory Server is able to
translate E.164-t to the IP address of MTA-t (one of the MTAs
managed by Proxy-t). Proxy-t then checks to see if MTA-t is
authorized for receiving this call. Proxy-talso checks the account
information to determine if MTA-o is paying for the call or if MTA-t
is expected to pay. Proxy-t generates the following INVITE message
and sends it to MTA-t. The Remote-Party-ID line appears unchanged
only if the destination MTA has subscribed to caller-id service;
otherwise, or if the caller had specified privacy of the caller
information, the Remote-Party-ID line would be altered. Note that
the Via lines have been encrypted, maintaining the privacy of the
caller. The line State has been added, and contains all the
information needed by the Proxy for any subsequent call features
that may be requested. This information is signed by Proxy-t and
encrypted.
Upon sending this INVITE message, Proxy-t starts the retransmisison
timer (T-proxy-request) and starts the T3 session timer (T-proxy-
setup). The retransmission timer is cancelled on receipt of the
optional 100-Trying provisional response (not present in this call
flow); both are cancelled on receipt of the 183-Session-Progress
provisional response.
(2) INVITE:
INVITE sip:555-2222@Host(mta-t.provider); user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"}K
Supported: 100rel, state
Require: state
Remote-Party-ID: John Doe; <tel:+1-212-555-1111>
Media-Authorization: 31S14621
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider);gate=Host(cmts-t.provider):4321/31S14621}K"
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:Host(cms-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mg02.provider)
b=AS:64
t=907165275 0
DCS Group Category: Informational - Expiration 8/31/02 45
DCS Architecture February 2002
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Upon receiving this INVITE, MTA-t authenticates that the message
came from Proxy-t using IPSec. MTA-t checks the telephone line
associated with the E.164-t (as found in the Request URI) to see if
it is available. If it is available, MTA-t looks at the capability
parameters in the Session Description Protocol (SDP) part of the
message and determines which media channel parameters it can
accommodate for this call. MTA-t stores the INVITE message,
including the encrypted State parameters, for later use. MTA-t
puts this line in the "busy" state (so any other call attempts are
rejected until this call clears), generates the following 183-
Session-Progress response, and sends it to Proxy-t. MTA-t starts
the retransmission timer with value (T-proxy-response) and starts
the session timer (T3) with value (T-resource).
MTA-t can, at its option, still accept further incoming calls and
present them all to the customer. Such enhanced user interfaces for
the MTA is beyond the scope of this specification. Note that MTA-t
can't use the To: header field to determine the proper line, as it
may be totally unrelated to the phone number at MTA-t.
(3) 183-Session-Progress:
SIP/2.0 183 Session Progress
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"}K
Require: 100rel
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider);gate=Host(cmts-t.provider):4321/31S14621}K"
Remote-Party-ID: John Smith <tel:555-2222>
Anonymity: off
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Rseq: 9021
Content-Disposition: precondition
Contact: sip:Host(mta-t.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-t.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
DCS Group Category: Informational - Expiration 8/31/02 46
DCS Architecture February 2002
a=rtpmap:0 PCMU/8000
m=audio 6544 RTP/AVP 0
a=qos:mandatory sendrecv confirm
Upon receiving the 183-Session-Progress message, Proxy-t forwards
the following message to CMS-o, restoring the Via headers, and
adding Dcs-Gate information. At this point Proxy-t has completed
all the call processing functions needed for this call, deletes its
local state information, and handles all remaining messages as a
stateless proxy. Proxy-t may include Dcs-Billing-Information if it
wishes to override the billing information that came in the INVITE
(e.g. collect or toll-free call).
(4) 183-Session-Progress:
SIP/2.0 183 Session Progress
Via: SIP/2.0/UDP Host(dp-o.provider);branch=1
Require: 100rel, state
State: Host(dp-t.provider); nexthop=sip:Host(dp-o.provider);
gate=Host(cmts-t.provider):4321/31S14621; orig-
dest=tel:+1-212-555-1111; num-redirects=0
Dcs-Gate: Host(cmts-t.provider):4321/31S14621/37FA1948
Remote-Party-ID: John Smith <tel:+1-212-555-2222>
Anonymity: off
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Rseq: 9021
Content-Disposition: precondition
Contact: sip:Host(mta-t.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-t.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=rtpmap:0 PCMU/8000
m=audio 6544 RTP/AVP 0
a=qos:mandatory sendrecv confirm
Upon receiving the 183-Session-Progress message, CMS-o stops timer
(T-proxy-request) and sends the following PRACK message directly to
MTA-t using the IP address in the Contact header of the 183-Session-
Progress message.
(5) PRACK:
PRACK sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(cms-o.provider)
From: John Doe; <tel:+1-212-555-1111>
DCS Group Category: Informational - Expiration 8/31/02 47
DCS Architecture February 2002
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 128 PRACK
Rack: 9021 127 INVITE
Content-Type: application/sdp
Content-length: (.)
v=0
O=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mg02.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 3456 RTP/AVP 0
a-qos:mandatory sendrecv
MTA-t acknowledges the PRACK with a 200-OK, and begins to reserve
the resources necessary for the call.
(6) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(cms-o.provider)
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 128 PRACK
After sending PRACK(5), CMS-o signals to the endpoint device to
attempt to reserve the network resources necessary for the
connection. If the endpoint signals that resource reservation is
successful, CMS-o sends the following COMET message directly to MTA-
t. CMS-o starts timer (T-direct-request).
(7) COMET:
COMET sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(cms-o.provider)
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 COMET
Content-Type: application/sdp
Content-length: (.)
v=0
O=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mg02.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
DCS Group Category: Informational - Expiration 8/31/02 48
DCS Architecture February 2002
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 3456 RTP/AVP 0
a=qos:success send
MTA-t acknowledges the COMET message with a 200-OK.
(8) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(cms-o.provider)
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 COMET
Upon receipt of the 200-OK(10), CMS-o stops timer (T-direct-
request).
Upon receipt of the (5) PRACK message, MTA-t stops timer (T-proxy-
response) and attempts to reserve network resources if necessary.
Once MTA-t both receives the COMET message and has successfully
reserved network resources, MTA-t begins to send ringing voltage to
the designated line and sends the following 180 RINGING message
through Proxy-t. MTA-t restarts the session timer(T3) with value
(T-ringing).
(9) 180 RINGING:
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"}K
Require: 100rel
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider);gate=Host(cmts-t.provider):4321/31S14621}K"
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Contact: sip:Host(mta-t.provider)
Cseq: 127 INVITE
Rseq: 9022
Proxy-t decodes the Via: headers, and passes the 180-Ringing to CMS-
o. This operation is done as a SIP stateless proxy.
(10) 180 RINGING:
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP Host(cms-o.provider);branch=1
Require: 100rel
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Contact: sip:Host(mta-t.provider)
Cseq: 127 INVITE
RSeq: 9022
DCS Group Category: Informational - Expiration 8/31/02 49
DCS Architecture February 2002
Upon receipt of the 180 RINGING message, CMS-o restarts the
transaction timer (T3) with value (T-ringing). CMS-o acknowledges
the provisional response with a PRACK, and signals the endpoint
device to play audible ringback tone to the customer.
(11) PRACK:
PRACK sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(cms-o.provider)
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 130 PRACK
RAck: 9022 127 INVITE
MTA-t acknowledges the PRACK with a 200-OK, and stops timer (T-
proxy-response).
(12) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(cms-o.provider)
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 130 PRACK
Once MTA-t detects off-hook on the called line, it disconnects
ringing voltage from the line and sends the final response through
the proxies. MTA-t stops timer (T-ringing) and starts timer (T-
proxy-response). If necessary, MTA-t may also commit to resources
that have been reserved for this call. At this point, MTA-t begins
to generate bearer channel packets of encoded voice and send them to
MTA-o using the IP address and port number specified in the SDP part
of the original INVITE message.
(13) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"}K
State: Host(dp-t.provider); state="{nexthop=sip:Host(cms-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
via="Host(cms-o.provider);branch=1"}K"
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Proxy-t handles the message as a SIP stateless proxy, and forwards
it to CMS-o.
(14) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(dp-o.provider);branch=1
DCS Group Category: Informational - Expiration 8/31/02 50
DCS Architecture February 2002
Via: SIP/2.0/UDP Host(mta-o.provider)
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Upon receipt of the 200-OK message, CMS-o stops timer (T-ringing)
and signals the endpoint device to stop playing audible ringback
tone to the customer and to begin to play the bearer channel stream
that is received from MTA-t. CMS-o sends the following ACK message
to MTA-t. If necessary, CMS-o may also commit to resources that have
been reserved for this call. At this point, the endpoint device
begins to generate bearer channel packets of encoded voice and send
them to MTA-t using the IP address and port number specified in the
SDP part of the original 183-Session-Progress message (that was a
response to the original INVITE).
(15) ACK:
ACK sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(cms-o.provider)
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 ACK
Upon receipt of the ACK message, MTA-t stop timer (T-proxy-
response).
When either endpoint detects hangup, it sends out a BYE message to
the other one. In this example, MTA-t detected that the customer
hung up the phone. MTA-t puts that line in the "idle" state so new
calls can be made or received. It sends the following BYE message
directly to CMS-o. MTA-t may also need to release network resources
that have been used for the call. MTA-t starts timer (T-direct-
request).
(16) BYE:
BYE sip:Host(cms-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-t.provider)
From: tel:+1-212-555-2222
To: John Doe; <tel:+1-212-555-1111>
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 131 BYE
Upon receipt of the BYE message, CMS-o signals the endpoint device
to stop playing the bearer channel stream received from MTA-t and,
if necessary, releases network resources that have been used for
this call. CMS-o sends the following 200-OK message to MTA-t. Once
hangup is detected on the endpoint device, CMS-o puts that line in
the "idle" state so new calls can be made or received.
(17) 200-OK:
SIP/2.0 200 OK
DCS Group Category: Informational - Expiration 8/31/02 51
DCS Architecture February 2002
Via: SIP/2.0/UDP Host(mta-t.provider)
From: tel:+1-212-555-2222
To: John Doe; <tel:+1-212-555-1111>
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 131 BYE
Upon receipt of 200-OK, MTA-t stops timer (T-direct-request).
10.4 Basic Call Flow from CMS to CMS
Endpoint-o CMS-o CMS-t Endpoint-t
| Private Signaling | | |
|<------------------->|(1)INVITE | |
| |--------->| Private Signaling |
| | |<------------------->|
| |(2)183 SDP| |
| |<---------| |
| Private Signaling | | |
|<------------------->|(3)PRACK | |
| |--------->| |
| |(4)200 OK | Private Signaling |
| |<-------->|<------------------->|
| | | |
|<------------------Reserve Resources----------------->|
| | | |
| Private Signaling | | |
|<------------------->|(5)COMET | |
| |--------->| |
| |(6)200 OK | Private Signaling |
| |<-------->|<------------------->|
| | (7)180 | |
| Private Signaling |<---------| |
|<------------------->|(8)PRACK | |
| |--------->| |
| |(9)200 OK | |
| |<---------| | User
| | | Private Signaling | Answers
| | |<------------------->|
| | (10)200 | |
| Private Signaling |<---------| |
|<------------------->| (11)ACK | |
| |--------->| |
| | | |
|<--------------------Active Call-------------------->|
| | | | User
| | (12)BYE | Private Signaling | Hangs Up
| |<---------|<------------------->|
| |(13)200 OK| |
| |----------| |
DCS Group Category: Informational - Expiration 8/31/02 52
DCS Architecture February 2002
A call setup begins when the endpoint device controlled by CMS-o
detects an off-hook condition on one of its lines. This event is
communicated to CMS-o through a private signaling exchange beyond
the scope of this specification. CMS-o first puts that line in the
"busy" state, and collects a complete E.164 number. As a result of a
translation function performed by CMS-o, the destination is
determined to be an endpoint device served by CMS-t. CMS-o
generates the following SIP INVITE message and sends it to CMS-t.
CMS-o starts the retransmission timer (T-proxy-request) and starts
the T3 session timer (T-setup). The retransmission timer is
cancelled on receipt of the optional 100-Trying provisional response
(not present in this call flow); both are cancelled on receipt of
the 183-Session-Progress provisional response.
(1) INVITE:
INVITE sip:+1-212-555-2222;rn=+1-212-234-2222;
npdi=yes@Host(cms-t);user=phone SIP/2.0
Via: SIP/2.0/UDP Host(cms-o.provider);branch=1
Supported: 100rel, state
Require: state
Proxy-Require: dcs, state
Remote-Party-ID: John Doe; <tel:+1-212-555-1111>
Anonymity: Off
Dcs-Gate: Host(cms-o.provider):3612/17S30124/37FA1948 optional
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/212-
555-1111/212-555-2222>
Dcs-Billing-ID: Host(cms-o.provider):36123E5C:0152
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:Host(cms-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mg02.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Upon receiving this INVITE message, CMS-t authenticates that the
sender was CMS-o using IPSec, and sends the E.164-t address to the
directory server. In this example, the Directory Server is able to
translate E.164-t to the IP address of one of the endpoint devices
DCS Group Category: Informational - Expiration 8/31/02 53
DCS Architecture February 2002
controlled by CMS-t. CMS-t then checks to see if the endpoint
device is authorized for receiving this call. CMS-talso checks the
account information to determine if the originator is paying for the
call or if the destination is expected to pay. CMS-t engages in
private signaling exchange with the endpoint device, beyond the
scope of this specification, and determines the SDP description of
the media stream to be sent to this endpoint.
CMS-t puts this line in the "busy" state (so any other call attempts
are rejected until this call clears), generates the following 183-
Session-Progress response, and sends it to CMS-o. The Dcs-Gate
header is omitted from this message, since CMS-o indicated it was
optional, and CMS-t considers it optional as well. CMS-t starts the
retransmission timer with value (T-proxy-response) and starts the
session timer (T3) with value (T-resource). CMS-t may include Dcs-
Billing-Information if it wishes to override the billing information
that came in the INVITE (e.g. collect or toll-free call).
(2) 183-Session-Progress:
SIP/2.0 183 Session Progress
Via: SIP/2.0/UDP Host(cms-o.provider);branch=1
Require: 100rel, state
Proxy-Require: dcs, state
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Rseq: 9021
Content-Disposition: precondition
Contact: sip:Host(cms-t.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(rgw12.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=rtpmap:0 PCMU/8000
m=audio 6544 RTP/AVP 0
a=qos:mandatory sendrecv confirm
Upon receiving the 183-Session-Progress message, CMS-o stops timer
(T-proxy-request) and sends the following PRACK message to CMS-t
using the IP address in the Contact header of the 183-Session-
Progress message.
(3) PRACK:
PRACK sip:Host(cms-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(cms-o.provider)
From: John Doe; <tel:+1-212-555-1111>
DCS Group Category: Informational - Expiration 8/31/02 54
DCS Architecture February 2002
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 128 PRACK
Rack: 9021 127 INVITE
Content-Type: application/sdp
Content-length: (.)
v=0
O=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mg02.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 3456 RTP/AVP 0
a-qos:mandatory sendrecv
CMS-t acknowledges the PRACK with a 200-OK, and signals the endpoint
device to begin to reserve the resources necessary for the call.
(4) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(cms-o.provider)
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 128 PRACK
After sending PRACK(3), CMS-o signals to the endpoint device to
attempt to reserve the network resources necessary for the
connection. If the endpoint signals that resource reservation is
successful, CMS-o sends the following COMET message to CMS-t. CMS-o
starts timer (T-direct-request).
(5) COMET:
COMET sip:Host(cms-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(cms-o.provider)
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 COMET
Content-Type: application/sdp
Content-length: (.)
v=0
O=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mg02.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
DCS Group Category: Informational - Expiration 8/31/02 55
DCS Architecture February 2002
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 3456 RTP/AVP 0
a=qos:success send
CMS-t acknowledges the COMET message with a 200-OK.
(6) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(cms-o.provider)
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 COMET
Upon receipt of the 200-OK(6), CMS-o stops timer (T-direct-request).
Upon receipt of the (3) PRACK message, CMS-t stops timer (T-proxy-
response) and attempts to reserve network resources if necessary.
Once CMS-t both receives the COMET message and has successfully
reserved network resources, CMS-t signals the endpoint to begin to
send ringing voltage to the designated line and sends the following
180 RINGING message. CMS-t restarts the session timer (T3) with
value (T-ringing).
(7) 180 RINGING:
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP Host(cms-o.provider);branch=1
Require: 100rel
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Contact: sip:Host(cms-t.provider)
Cseq: 127 INVITE
Rseq: 9022
Upon receipt of the 180 RINGING message, CMS-o restarts the
transaction timer (T3) with value (T-ringing). CMS-o acknowledges
the provisional response with a PRACK, and signals the endpoint
device to play audible ringback tone to the customer.
(8) PRACK:
PRACK sip:Host(cms-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(cms-o.provider)
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 130 PRACK
RAck: 9022 127 INVITE
CMS-t acknowledges the PRACK with a 200-OK, and stops timer (T-
proxy-response).
(9) 200 OK:
DCS Group Category: Informational - Expiration 8/31/02 56
DCS Architecture February 2002
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(cms-o.provider)
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 130 PRACK
Once CMS-t detects off-hook on the called line, it disconnects
ringing voltage from the line and sends the final response. CMS-t
stops timer (T-ringing) and starts timer (T-proxy-response). If
necessary, CMS-t may also commit to resources that have been
reserved for this call. At this point, CMS-t signals to the
endpoint device to begin to generate bearer channel packets of
encoded voice and send them to the originating endpoint, at the IP
address and port number specified in the SDP part of the original
INVITE message.
(10) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(cms-o.provider); branch=1
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Upon receipt of the 200-OK message, CMS-o stops timer (T-ringing)
and signals the endpoint device to stop playing audible ringback
tone to the customer and to begin to play the bearer channel stream
that is received from the destination endpoint. CMS-o sends the
following ACK message to CMS-t. If necessary, CMS-o may also commit
to resources that have been reserved for this call. At this point,
the endpoint device begins to generate bearer channel packets of
encoded voice and send them to the destination endpoint using the IP
address and port number specified in the SDP part of the original
183-Session-Progress message (that was a response to the original
INVITE).
(11) ACK:
ACK sip:Host(cms-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(cms-o.provider)
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 ACK
Upon receipt of the ACK message, CMS-t stop timer (T-proxy-
response).
When either endpoint detects hangup, it sends out a BYE message to
the other one. In this example, the originating endpoint detected
that the customer hung up the phone. CMS-o puts that line in the
"idle" state so new calls can be made or received. It sends the
DCS Group Category: Informational - Expiration 8/31/02 57
DCS Architecture February 2002
following BYE message directly to CMS-t. CMS-o starts timer (T-
direct-request).
(12) BYE:
BYE sip:Host(cms-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(cms-o.provider)
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 131 BYE
Upon receipt of the BYE message, CMS-t signals the endpoint device
to stop playing the bearer channel stream received from the
originator and, if necessary, releases network resources that have
been used for this call. CMS-tsends the following 200-OK message to
CMS-o. Once hangup is detected on the endpoint device, CMS-t puts
that line in the "idle" state so new calls can be made or received.
(13) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(cms-o.provider)
From: John Doe; <tel:+1-212-555-1111>
To: tel:+1-212-555-2222
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 131 BYE
Upon receipt of 200-OK, CMS-o stops timer (T-direct-request).
DCS Group Category: Informational - Expiration 8/31/02 58
DCS Architecture February 2002
10.5 Call-Forwarding-Unconditional and Call-Forwarding-Busy
MTA-o Proxy-o Proxy-t MTA-t
| INVITE | | |
|----------------->| INVITE | |
| |-------------->| (1)INVITE |
| | |------------------>|
| | | (2)302 Redirect |
| | |<------------------|
| | (3)302 | |
| |<--------------| (4)ACK |
| | |------------------>|
| | (5)ACK | |
| |-------------->| |
| |
| | Proxy-f MTA-f
| | | |
| | (6)INVITE | |
| |-------------->| (7)INVITE |
| | |------------------>|
| | | (8)183 SDP |
| | |<------------------|
| | | |
The initial call flow for Call-Forwarding-Unconditional/Busy is
identical to that shown in Section 10.1 until MTA-t receives the
following INVITE message from Proxy-t.
(1) INVITE:
INVITE sip:555-2222@Host(mta-t.provider); user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
Supported: 100rel, state
Require: state
Remote-Party-ID: John Doe <tel:+1-212-555-1111>
Media-Authorization: 31S14621
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
DCS Group Category: Informational - Expiration 8/31/02 59
DCS Architecture February 2002
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Upon receiving this message, MTA-t determines that the line
associated with 212-555-2222 is having all calls forwarded. It may
initiate some local action (e.g. to play special ringing tones) to
provide notification that the call is being forwarded. It may
perform some functions as a SIP proxy, using the received Call-ID
and SDP description, to further locate the user. It then issues a
REDIRECT (302) response to indicate that it wants the call
forwarded. This message carries the forwarding number in the Contact
header.
(2) 302-Redirect
SIP/2.0 302 Moved Temporarily
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
Remote-Party-ID: John Smith <tel:555-2222>
Anonymity: off
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: tel:555-3333
Proxy-t verifies on receipt of the 302-Redirect message that the
called party is a subscriber to the Call Forwarding service. Proxy-t
also verifies that the called party is permitted to forward the call
to the supplied destination. It then adds a DCS-billing field to
the 302-Redirect message to allow the "second leg" of the forwarded
call to be charged to the user associated with 212-555-2222. It also
DCS Group Category: Informational - Expiration 8/31/02 60
DCS Architecture February 2002
restores the suppressed Via headers to allow the response to be
routed back to Proxy-o.
(3) 302-Redirect
SIP/2.0 302 Moved Temporarily
Via: SIP/2.0/UDP Host(dp-o.provider); branch = 1
Via: SIP/2.0/UDP Host(mta-o.provider)
Proxy-Require: dcs
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/212-
555-1111/212-555-2222>
Dcs-Billing-Info: Host(rks-t.provider)<4278-9865-8765-9000/212-
555-2222/212-555-3333>
Dcs-Billing-ID: Host(dp-o.provider):36123E5C:0152
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124;
orig-dest=tel:+1-212-555-2222; num-redirects=0
Remote-Party-ID: John Smith <tel:+1-212-555-2222>
Anonymity: off
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: tel:+1-212-555-3333
Proxy-t also sends an ACK to MTA-t.
(4) ACK
ACK sip:555-2222@Host(mta-t.provider); user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-t.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 ACK
The transaction at MTA-t is now complete.
Proxy-o matches the 302 response to the INVITE it had sent out. It
sends an ACK back to Proxy-t .
(5) ACK
ACK sip:555-2222@Host(mta-t.provider); user=phone SIP/2.0
Via: Sip/2.0/UDP Host(dp-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
CSeq: 127 ACK
The transaction at Proxy-t is now complete.
DCS Group Category: Informational - Expiration 8/31/02 61
DCS Architecture February 2002
Proxy-o determines the Proxy-f for the E.164 number 212-555-3333
when it receives the 302-Redirect message. It generates an INVITE
message and sends it to Proxy-f. It embeds two Dcs-Billing-Info
headers in this message. The first one identifies the user
associated with the E.164 number 212-555-1111 as paying for the
initial call leg (212-555-1111/212-555-2222). The second one
identifies the user associated with the E.164 number 212-555-2222 as
paying for the second call leg (212-555-2222/212-555-3333). Proxy-o
adds the Dcs-Redirect header giving the information about this call
redirection.
(6) INVITE:
INVITE sip:+1-212-555-3333;rn=+1-212-265-3333;
npdi=yes@Host(dp-f) ;user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-o.provider); branch = 2
Via: SIP/2.0/UDP Host(mta-o.provider);
Supported: 100rel, state
Require: state
Proxy-Require: dcs, state
Remote-Party-ID: John Doe; <tel:+1-212-555-1111>
Anonymity: Off
Dcs-Gate: Host(cmts-o.provider):3612/17S30124/37FA1948 required
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/212-
555-1111/212-555-2222>
Dcs-Billing-Info: Host(rks-t.provider)<4278-9865-8765-9000/212-
555-2222/212-555-3333>
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124;
orig-dest=tel:+1-212-555-2222; num-redirects=1
Dcs-Billing-ID: Host(dp-o.provider):36123E5C:0152
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
CSeq: 127 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
DCS Group Category: Informational - Expiration 8/31/02 62
DCS Architecture February 2002
Upon receiving this INVITE, Proxy-f queries the directory server to
determine the IP address (MTA-f) associated with 212-555-3333. It
then forwards the INVITE message to MTA-f.
(7) INVITE:
INVITE sip:555-3333@Host(mta-f.provider); user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-f.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
Supported: 100rel, state
Require: state
Remote-Party-ID: John Doe <tel:+1-212-555-1111>
Media-Authorization: 22S21718
State: Host(dp-f.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-f.provider):4321/22S21718;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=1"}K"
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Upon receiving this INVITE, MTA-f authenticates that the message
came from Proxy-f using IPSec. It checks the telephone line
associated with the E.164-f to see if it is available. If it is
available, MTA-f looks at the capability parameters in the Session
Description Protocol (SDP) part of the message and determines which
media channel parameters it can accommodate for this call. MTA-f
stores the INVITE message, including the encrypted State parameters,
for later use. MTA-f puts this line in the "busy" state (so any
other call attempts are rejected until this call clears), generates
the following 183-Session-Progress response, and sends it to Proxy-
f. MTA-f starts timer (T-proxy-response).
DCS Group Category: Informational - Expiration 8/31/02 63
DCS Architecture February 2002
(8) 183-Session-Progress:
SIP/2.0 183 Session Progress
Via: SIP/2.0/UDP Host(dp-f.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
Require: 100rel
State: Host(dp-f.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-f.provider):4321/22S21718;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=1"}K"
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Rseq: 9021
Content-Disposition: precondition
Contact: sip:Host(mta-f.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-f.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=rtpmap:0 PCMU/8000
m=audio 6544 RTP/AVP 0
a=qos:mandatory sendrecv confirm
The subsequent signaling call flows are identical to those shown in
Section 10.1.
DCS Group Category: Informational - Expiration 8/31/02 64
DCS Architecture February 2002
10.6 Call-Forwarding-No-Answer
MTA-o Proxy-o Proxy-t MTA-t
... ... ... ...
| | | |
| | | (1)180 Ringing |
| | |<------------------|
| |(2)180 Ringing | |
| (3)180 Ringing |<--------------| |
|<-----------------| | |
| | (4)PRACK | |
|----------------------------------------------------->|
| | (5)200 OK | |
|<-----------------------------------------------------|
| | | |
| | | |
| | | (6)302 Redirect |
| | |<------------------|
| | (7)302 | |
| (8)302 Redirect |<--------------| (9)ACK |
|<-----------------| |------------------>|
| | (10)ACK | |
| (11) ACK |-------------->| |
|----------------->|
| | Proxy-f MTA-f
| (12) INVITE | | |
|----------------->| (13)INVITE | |
| |-------------->| (14)INVITE |
| | |------------------>|
| | | |
The Call Forwarding No Answer service is triggered when a called
party does not pick up the phone after it rings for a pre-specified
period of time. The subsequent call flow is different from that for
the Call Forwarding Busy and Call Forwarding Unconditional services
since the originating and terminating MTAs have already identified
each other, have already reserved the resources for the call, and
since the CMS/Proxies are no longer storing transaction state when
the Forwarding function is triggered.
The initial set of messages for this service are the same as in
Section 10.1 through the point at which MTA-t is ringing the phone,
and MTA-o is generating ringback. For purposes of this example,
consider the initial INVITE message received by MTA-t to be the
following.
(not shown) INVITE:
DCS Group Category: Informational - Expiration 8/31/02 65
DCS Architecture February 2002
INVITE sip:555-2222@Host(mta-t.provider); user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
Supported: 100rel, state
Require: state
Remote-Party-ID: John Doe <tel:+1-212-555-1111>
Media-Authorization: 31S14621
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
In response to the INVITE message, MTA-t starts local ringback and
sends a 180 RINGING notification to MTA-o. It also starts the timer
(T-ringing).
(1) 180 RINGING:
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
Require: 100rel
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
DCS Group Category: Informational - Expiration 8/31/02 66
DCS Architecture February 2002
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Contact: sip:Host(mta-o.provider)
Cseq: 127 INVITE
Rseq: 9022
The 180-Ringing message from Proxy-t to Proxy-o (2), the 180-Ringing
message from Proxy-o to MTA-o (3), and the PRACK exchange (4) and
(5), are identical to the basic call flow in Section 10.1, and not
repeated here.
When the timer(T-ringing) at the MTA-t expires, it determines the
forwarding number (555-3333) and sends a 302-Redirect response with
this number in the Contact header.
(6) 302-Redirect
SIP/2.0 302 Moved Temporarily
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: tel:555-3333
Proxy-t uses its IPSec association with MTA-t to determine the
identity of the request. It then verifies the line subscribes to
the Call-Forwarding-No-Answer service. Proxy-t uses its State value
to recover the billing information for the current call (which is
either stored directly in the State value, or stored indirectly with
a pointer to the Gate which stores the billing information). Proxy-
t adds an additional Dcs-Billing-Info header containing the billing
information for the second leg of the forwarded call. Proxy-t
converts the new destination number in the Contact header into a
full E.164 number, and passes the 302-Redirect message to Proxy-o.
(7) 302-Redirect
SIP/2.0 302 Moved Temporarily
Via: SIP/2.0/UDP Host(dp-o.provider); branch = 1
Via: SIP/2.0/UDP Host(mta-o.provider)
Proxy-Require: dcs
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/212-
555-1111/212-555-2222>
Dcs-Billing-Info: Host(rks-t.provider)<4278-9865-8765-9000/212-
555-2222/212-555-3333>
Dcs-Billing-ID: Host(dp-o.provider):36123E5C:0152
DCS Group Category: Informational - Expiration 8/31/02 67
DCS Architecture February 2002
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124;
orig-dest=tel:+1-212-555-2222; num-redirects=0
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: tel:+1-212-555-3333
Proxy-o converts the Contact header into a private format URL
containing the billing information and usage restrictions for the
new call. By including a timestamp, Proxy-o insures the URL can't
be used for later call attempts beyond those authorized by the
forwarder. Also encoded in the URL is the information needed for
the Dcs-Redirect header and any required LAES.
(8) 302-Redirect
SIP/2.0 302 Moved Temporarily
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:{type=transfer; dest=tel:+1-212-555-3333; billing-
info= Host(rks-o.provider)<5123-0123-4567-8900/212-555-
1111/212-555-2222>; billing-info= Host(rks-
t.provider)<4278-9865-8765-9000/212-555-2222/212-555-
3333>; billing-id= Host(dp-o.provider):36123E5C:0152;
expires=36123E9A; orig-dest=+1-212-555-2222;
redirected-by=+1-212-555-2222; num-
redirects=1}K@Host(dp-o.provider);user=private
Proxy-t sends the following ACK message to MTA-t after sending 302-
Redirect(8).
(9) ACK
ACK sip:555-2222@Host(mta-t.provider); user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-t.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 ACK
Proxy-o sends the following ACK message to Proxy-t after sending
302-Redirect(9).
(10) ACK
ACK sip:555-2222@Host(mta-t.provider); user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-o.provider)
DCS Group Category: Informational - Expiration 8/31/02 68
DCS Architecture February 2002
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 ACK
MTA-o sends the following ACK message to Proxy-o on receipt of the
302-Redirect(8).
(11) ACK
ACK sip:555-2222@Host(mta-t.provider); user=phone SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 ACK
The transaction at Proxy-o, Proxy-t and MTA-t is now complete.
MTA-o, if it so desires, may now initiate a new call to the
destination given in the Contact header. To avoid confusion at MTA-
o, the call leg identification for this new call is different from
that of the previous call. Therefore, any stored State headers are
not included in this INVITE, and only the Request-URI gives the
handling and billing information.
(12) INVITE:
INVITE sip:{type=transfer; dest=tel:+1-212-555-3333; billing-
info= Host(rks-o.provider)<5123-0123-4567-8900/212-555-
1111/212-555-2222>; billing-info= Host(rks-
t.provider)<4278-9865-8765-9000/212-555-2222/212-555-
3333>; billing-id= Host(dp-o.provider):36123E5C:0152;
expires=36123E9A; orig-dest=+1-212-555-2222;
redirected-by=+1-212-555-2222; num-
redirects=1}K@Host(dp-o.provider);user=private SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
Remote-Party-ID: John Doe <tel:555-1111>
Anonymity: Off
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E98;
seq=74))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E98; seq=75))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E98;seq=74))@localhost
Cseq: 127 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
DCS Group Category: Informational - Expiration 8/31/02 69
DCS Architecture February 2002
b=AS:64
t=907165275 0
a=X-pc-csuite:312F
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc- codecs:96
Proxy-o does all its normal authorization and authentication
functions, and decodes the encrypted private username in the
Request-URI. From that it builds the Dcs-Billing-Info, Dcs-Billing-
ID, and Dcs-Redirect headers, and determines the destination
address. The INVITE message sent on to Proxy-f is as follows.
(13) INVITE:
INVITE sip:+1-212-555-3333;rn=+1-212-265-3333;
npdi=yes@Host(dp-f);user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-o.provider);branch=2
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
Require: state
Proxy-Require: dcs, state
Remote-Party-ID: John Doe; <tel:+1-212-555-1111>
Anonymity: Off
Dcs-Gate: Host(cmts-o.provider):3612/3S73916/518C3B22 required
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/212-
555-1111/212-555-2222>
Dcs-Billing-Info: Host(rks-t.provider)<4278-9865-8765-9000/212-
555-2222/212-555-3333>
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/3S73916;
orig-dest=tel:+1-212-555-2222; num-redirects=1
Dcs-Billing-ID: Host(dp-o.provider):36123E98:0171
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E98;
seq=74))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E98; seq=75))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E98;seq=74))@localhost
Cseq: 127 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
DCS Group Category: Informational - Expiration 8/31/02 70
DCS Architecture February 2002
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
The remainder of the call procedes as in Section 10.1.
10.7 Call-Forwarding-MTA-Unavailable
MTA-o Proxy-o Proxy-t MTA-t
| | | (1) REGISTER |
| | |<------------------|
| | | (2)200 OK |
| | |------------------>|
| | | |
| INVITE | | |
|----------------->| INVITE | |
| |-------------->| INVITE |
| | |------------------>|
| | | |
| | (Timeout) |
| | | |
| | 302 REDIRECT | |
| |<--------------| |
| | ACK | |
| |-------------->| |
| |
| | Proxy-f MTA-f
| | | |
| | INVITE | |
| |-------------->| INVITE |
| | |------------------>|
| | | |
This service consists of two parts. First, the MTA must register
the forwarding address with the Proxy. Later, when an incomming
call is handled by the proxy and the MTA is not available, the Proxy
initiates the call forwarding.
MTA-t recognizes that the customer dialed the code to activate Call
Forwarding, and prompts the customer for the forwarding telephone
number. This information is sent to the Proxy in a REGISTER
message.
(1) REGISTER
REGISTER sip:Host(dp-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-t.provider)
From: sip:555-2222@Host(mta-t.provider); user=phone
To: sip:Host(dp-o.provider)
Call-ID: B64(SHA-1(555-2222;time=361013B8;seq=1))
Cseq: 1 REGISTER
DCS Group Category: Informational - Expiration 8/31/02 71
DCS Architecture February 2002
Contact: tel:555-3333
Expires: 7200
The Proxy validates that the forwarding number maps to either a MTA
it knows about or to another valid Proxy. The Proxy also checks to
make sure that the customer subscribes to the Call Forwarding
service, and if so activates the service and stores the forwarding
number for later use. It responds to the MTA with a 200-OK.
(2) 200-OK
SIP 2.0 200 OK
Via: SIP/2.0/UDP Host(mta-t.provider)
From: sip:555-2222@Host(mta-t.provider); user=phone
To: sip:Host(dp-o.provider)
Call-ID: B64(SHA-1(555-2222;time=361013B8;seq=1))
Cseq: 1 REGISTER
For an incomming call, the initial sequence of messages is identical
to that for a regular call setup as shown in Section 10.1, until
Proxy-t forwards the INVITE message to MTA-t. Proxy-t times out when
it does not receive a response to the INVITE from MTA-t. It
determines that the called party subscribes to Call Forwarding
service and that the forwarding number is 212-555-3333. It then
generates a SIP 302 (Redirect) message with the forwarding number in
the Contact header. It then adds the DCS-billing and Dcs-Billing-ID
fields to the 302 message that allows the second leg of the
forwarded call to be charged to the user associated with 212-555-
2222. The subsequent call flow is the same as with Call Forwarding
Unconditional, (or Call Forwarding Busy), and is given in Section
10.5.
DCS Group Category: Informational - Expiration 8/31/02 72
DCS Architecture February 2002
10.8 Return-Call
MTA-o Proxy-o Proxy-t MTA-t
| (1) INVITE | | |
|----------------->| (2) INVITE | |
| |-------------->| (3) INVITE |
| | |------------------>|
| | | (4) 183 SDP |
| | (5) 183 SDP |<------------------|
| (6) 183 SDP |<--------------| |
|<-----------------| (7) PRACK | |
|----------------------------------------------------->|
| | (8) 200 OK | |
|<-----------------------------------------------------|
| | (9) COMET | |
|----------------------------------------------------->|
| | (10) 200 OK | |
|<-----------------------------------------------------|
| | | (11) 180 Ringing |
| |(12)180Ringing |<------------------|
| (13)180 Ringing |<--------------| |
|<-----------------| (14) PRACK | |
|----------------------------------------------------->|
| | (15) 200 OK | |
|<-----------------------------------------------------|
| | | |
| (16) CANCEL | | |
|----------------->| (17) CANCEL | |
| |-------------->| (18) CANCEL |
| | |------------------>|
| | | (19) 200 OK |
| | (20) 200 OK |<------------------|
| (21) 200 OK |<--------------| |
|<-----------------| | |
| | | |
| | | (22) INVITE |
| | (23) INVITE |<------------------|
| |<--------------| |
We assume for this example that MTA-t had last received a call from
MTA-o. The INVITE message forwarded to MTA-o included the Remote-
Party-ID line, which contained, among other items, a URL that
identified MTA-o. If the original caller did not request privacy,
and the destination subscribed to caller-id, then the URL contains
the E.164 number, which can be used to place the return call. We
DCS Group Category: Informational - Expiration 8/31/02 73
DCS Architecture February 2002
assume for this example that was not the case, and that MTA-t does
not know the identity of the new call's destination.
Messages (1) through (15) in the above diagram are identical to
those for the basic call flow given in Section 10.1, and message
(16) through (21) is a standard SIP CANCEL operation. The key
parameters used in processing the return-call are contained in
message (3), reproduced below. For purposes of this example, we
assume the destination had not subscribed to Caller-ID service, and
therefore the calling-name and calling-number information is not
present in (3) INVITE.
(3) INVITE:
INVITE sip:555-2222@Host(mta-t.provider); user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
Supported: 100rel, state
Require: state
Remote-Party-ID: <sip:{type=remote-id; orig=tel:+1-212-555-
1111; otherstuff=whatever}K@Host(dp-t.provider);
user=private>; rpi-id=na
Media-Authorization: 31S14621
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
DCS Group Category: Informational - Expiration 8/31/02 74
DCS Architecture February 2002
Upon the user dialing *69, MTA-t initiates a call by sending an
INVITE message to its Proxy, with the Request-URI containing the URL
for the call to be returned. The complete message is as follows.
(22) INVITE:
INVITE sip:{type=remote-id; orig=tel:+1-212-555-1111;
otherstuff=whatever}K@Host(dp-t.provider); user=private
SIP/2.0
Via: SIP/2.0/UDP Host(mta-t.provider)
Supported: 100rel, state
Remote-Party-ID: John Smith <tel:555-2222>
Anonymity: Off
From: sip:B64(SHA-1(555-2222; time=36123F12;seq=3))@localhost
To: sip:B64(SHA-1(*69; time=36123F12;seq=4))@localhost
Call-ID: B64(SHA-1(555-2222;time=36123F12;seq=3))@localhost
Cseq: 127 INVITE
Contact: sip:Host(mta-t.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-t.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 7242 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Upon receiving the INVITE message, Proxy-t authenticates MTA-t using
standard IPSec. Proxy-t decrypts the destination string using its
privately-held key, and checks its signature in the result. From
this string the real destination E.164 is extracted. Proxy-t checks
the "Remote-Party-ID:" line, and checks to see that this line
belongs to MTA-t, and has either subscribed to call-return service,
or is authorized to use the service and be charged on a per-use
basis. Proxy-t then performs all the regular call handling
functions, as described in the basic call flow. The message sent to
Proxy-o is the following, and the call proceeds identically to the
basic call flow from this point onward.
(23) INVITE:
INVITE sip:+1-212-555-1111;rn=+1-212-237-1111;
npdi=yes@Host(dp-o.provider);user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-t.provider);branch=1
Via: SIP/2.0/UDP Host(mta-t.provider)
Supported: 100rel, state
Require: state
Proxy-Require: dcs, state
DCS Group Category: Informational - Expiration 8/31/02 75
DCS Architecture February 2002
Remote-Party-ID: John Smith <tel:+1-212-555-2222>
Anonymity: Off
Dcs-Gate: Host(cmts-t.provider):4321/31S14621/37FA1948
Dcs-Billing-Info: Host(rks-t.provider)<5098-0987-6543-2100/212-
555-2222/212-555-1111/*69>
Dcs-Billing-ID: Host(dp-t.provider):36123F12:0381
State: Host(dp-t.provider); nexthop=sip:555-2222@Host(mta-
t.provider); gate=Host(cmts-t.provider):4321/31S14621
From: sip:B64(SHA-1(555-2222; time=36123F12;seq=3))@localhost
To: sip:B64(SHA-1(*69; time=36123F12;seq=4))@localhost
Call-ID: B64(SHA-1(555-2222;time=36123F12;seq=3))@localhost
Cseq: 127 INVITE
Contact: sip:Host(mta-t.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-t.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 7242 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Remainder of call proceeds identically to the basic call flow given
in Section 10.1.
DCS Group Category: Informational - Expiration 8/31/02 76
DCS Architecture February 2002
10.9 Customer-Originated-Trace
MTA-o Proxy-o Proxy-t MTA-t
| (1) INVITE | | |
|----------------->| (2) INVITE | |
| |-------------->| (3) INVITE |
| | |------------------>|
| | | (4) 183 SDP |
| | (5) 183 SDP |<------------------|
| (6) 183 SDP |<--------------| |
|<-----------------| (7) PRACK | |
|----------------------------------------------------->|
| | (8) 200 OK | |
|<-----------------------------------------------------|
| | (9) COMET | |
|----------------------------------------------------->|
| | (10) 200 OK | |
|<-----------------------------------------------------|
| | | (11) 180 Ringing |
| |(12)180Ringing |<------------------|
| (13)180 Ringing |<--------------| |
|<-----------------| (14) PRACK | |
|----------------------------------------------------->|
| | (15) 200 OK | |
|<-----------------------------------------------------|
| | | |
| | | (16) 200 OK |
| | (17) 200 OK |<------------------|
| (18) 200 OK |<--------------| |
|<-----------------| | |
| | | |
| | | (19) INVITE |
| | (20) INVITE|<------------------|
| | <---------| |
Call-trace (*57) is almost identical to return-call (*69), but the
action taken by the Proxy is to report the information to law
enforcement authorities, and complete the call either to the Service
Provider's office or to an announcement server (which tells the
customer to call the Service Provider's office).
(19) INVITE:
INVITE sip:call-trace@Host(dp-t.provider) SIP/2.0
DCS Group Category: Informational - Expiration 8/31/02 77
DCS Architecture February 2002
Via: SIP/2.0/UDP Host(mta-t.provider)
Supported: 100rel, state
Dcs-Trace-Party-ID: sip:{type=remote-id; orig=tel:+1-212-555-
1111; otherstuff=whatever}K@Host(dp-t.provider);
user=private
Remote-Party-ID: John Smith <tel:555-2222>
Anonymity: Off
From: sip:B64(SHA-1(555-2222; time=36123F12;seq=3))@localhost
To: sip:B64(SHA-1(*57; time=36123F12;seq=4))@localhost
Call-ID: B64(SHA-1(555-2222;time=36123F12;seq=3))@localhost
Cseq: 127 INVITE
Contact: sip:Host(mta-t.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-t.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 7242 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Proxy performs the reporting function and connects to either (1) an
announcement server telling customer the information is recorded,
and to now call the Business Office during normal business hours, or
(2) the Business Office.
DCS Group Category: Informational - Expiration 8/31/02 78
DCS Architecture February 2002
10.10 Call-Waiting
MTA-o2 MTA-o1 Proxy-o Proxy-t MTA-t
| (1) INVITE | | |
|----------------->| (2) INVITE | |
| | |-------------->| (3) INVITE |
| | | |------------------>|
| | | | (4) 183 SDP |
| | | (5) 183 SDP |<------------------|
| (6) 183 SDP |<--------------| |
|<-----------------| (7) PRACK | |
|----------------------------------------------------->|
| | | (8) 200 OK | |
|<-----------------------------------------------------|
| | | (9) COMET | |
|----------------------------------------------------->|
| | | (10) 200 OK | |
|<-----------------------------------------------------|
| | | | (11) 180 Ringing |
| | |(12)180Ringing |<------------------|
| (13)180 Ringing |<--------------| |
|<-----------------| (14) PRACK | |
|----------------------------------------------------->|
| | | (15) 200 OK | |
|<-----------------------------------------------------|
| | | (16) INVITE(Hold) |
| |<-----------------------------------------|
| | | (17) 200 OK |
| |----------------------------------------->|
| | | (18) ACK |
| |<-----------------------------------------|
| | | | (19) 200 OK |
| | | (20) 200 OK |<------------------|
| (21) 200 OK |<--------------| |
|<-----------------| | |
| | | | |
| | |(22) INVITE(Hold) |
|<-----------------------------------------------------|
| | | (23) 200 OK | |
|----------------------------------------------------->|
| | | (24) ACK | |
|<-----------------------------------------------------|
| | | (25) INVITE(Resume) |
| |<-----------------------------------------|
DCS Group Category: Informational - Expiration 8/31/02 79
DCS Architecture February 2002
| | | (26) 200 OK |
| |----------------------------------------->|
| | | (27) ACK |
| |<-----------------------------------------|
Call Waiting is a service that allows a customer to respond to an
incoming call during the time the phone line is busy. The customer
hears an audible alerting tone, and indicates acceptance of the new
call via a hookflash (putting the previous call on hold).
Subsequent hookflashes switch between the two active calls. The
originator of the second call may hear a distinctive ringback tone.
For this example, consider an existing call initiated by MTA-o1,
with the following call identification:
MTA-t state for call from MTA-o1 to MTA-t
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Contact: sip:Host(mta-o1.provider)
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o1.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o1.provider); nexthop=sip:555-
1111@Host(mta-o1.provider); gate=Host(cmts-
o1.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
Dcs-Billing-Info: Host(rks-o1.provider)/04FA37<5123-0123-4567-
8900/212-555-1111/212-555-2222>
Dcs-Billing-ID: Host(dp-o1.provider):36123E5C:0152
The initial set of messages associated with the second arriving
call, (1) through (13), as shown in the figure above, are very
similar to those involved in a Basic Call Setup and are not
explicitly enumerated below. After the initial INVITE exchange, the
state information stored for this new call is:
MTA-t state for call from MTA-o2 to MTA-t
From: sip:B64(SHA-1(555-3333; time=36124125;seq=23))@localhost
To: sip:B64(SHA-1(555-2222; time=36124125;seq=24)@localhost
Call-ID: B64(SHA-1(555-3333;time=36124125;seq=23))@localhost
Contact: sip:Host(mta-o2.provider)
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o2.provider); gate=Host(cmts-t.provider):4321/32S35378;
state="Host(dp-o2.provider); nexthop=sip:555-
3333@Host(mta-o2.provider); gate=Host(cmts-
o2.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
Dcs-Billing-Info: Host(rks-o2.provider)/173F419B<6010-4500-
6789-0123/212-555-3333/212-555-2222>
Dcs-Billing-ID: Host(dp-o2.provider):36124125:0031
DCS Group Category: Informational - Expiration 8/31/02 80
DCS Architecture February 2002
In response to the INVITE for the second incoming call, the user at
MTA-t is provided some indication of the second call, e.g. using a
special tone. If the user at MTA-t hits a flash hook in response to
this, MTA-t issues a INVITE(Hold) message to MTA-o1 to put it on
HOLD.
(16) INVITE (Hold):
INVITE sip:Host(mta-o1.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-t.provider)
From: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
To: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 INVITE
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 0.0.0.0
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 3456 RTP/AVP 0
MTA-o1 acknowledges the HOLD command with a 200-OK message. The
response contains an updated SDP description for the stream to be
received at MTA-o1, indicating an IP address of 0.0.0.0 for a held
call.
(17) 200-OK
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-t.provider)
From: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
To: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 INVITE
Content-Type: application/sdp
Content-length: (.)
v=0
O=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 0.0.0.0
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
DCS Group Category: Informational - Expiration 8/31/02 81
DCS Architecture February 2002
m=audio 6522 RTP/AVP 0
MTA-t responds to the 200-OK message with the standard SIP ACK
message. At this point it is safe for MTA-t to stop sending voice
payload packets to MTA-o1 and not risk dropping the connection due
to "dead MTA recovery."
(18) ACK
ACK Host(mta-o1.provider)
Via: SIP/2.0/UDP Host(mta-t.provider)
From: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
To: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 ACK
Once the first conversation is successfully placed on hold, MTA-t
indicates a completion to the "ringing" to MTA-o2.
(19) 200-OK
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o2.provider); gate=Host(cmts-t.provider):4321/32S35378;
state="Host(dp-o2.provider); nexthop=sip:555-
3333@Host(mta-o2.provider); gate=Host(cmts-
o2.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
From: sip:B64(SHA-1(555-3333;time=36124125;seq=23))@localhost
To: sip:B64(SHA-1(555-1111; time=36124125;seq=24)@localhost
Call-ID: B64(SHA-1(555-3333;time=36124125;seq=23))@localhost
Cseq: 128 INVITE
This 200-OK is passed through the proxy chain in messages (18) and
(19) to MTA-o2. MTA-o2 responds with an acknowledgement, in a manor
identical to the basic call flow.
(22) ACK
ACK Host(mta-t.provider)
Via: SIP/2.0/UDP Host(mta-o2.provider)
From: sip:B64(SHA-1(555-3333;time=36124125;seq=23))@localhost
To: sip:B64(SHA-1(555-1111; time=36124125;seq=24)@localhost
Call-ID: B64(SHA-1(555-3333;time=36124125;seq=23))@localhost
CSeq: 128 ACK
At this point the user at MTA-t has a connection to the second
caller, MTA-o2, with the first caller, MTA-o1, on hold.
Subsequent hookflashes repeat the sequence of INVITE(hold)/200-
OK/ACK to one destination, and INVITE(resume)/200-OK/ACK to the
other. The INVITE (Hold) sequence (22) through (24) is identical to
DCS Group Category: Informational - Expiration 8/31/02 82
DCS Architecture February 2002
(16) through (18). Once the 200-OK is received, it is safe for MTA-
t to stop sending voice packets.
INVITE (Resume) is very similar, except that the SDP description
includes the proper IP address in the "c=" line.
(25) INVITE (Resume):
INVITE sip:Host(mta-o1.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-t.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
CSeq: 130 INVITE
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-t.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 6544 RTP/AVP 0
MTA-o1 acknowledges the Resume command with a 200-OK message. The
response contains an updated SDP description for the stream to be
received at MTA-o1, indicating the real IP address of Host(mta-
o1.provider).
(26) 200-OK
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-t.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
CSeq: 129 INVITE
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o1.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
DCS Group Category: Informational - Expiration 8/31/02 83
DCS Architecture February 2002
m=audio 3456 RTP/AVP 0
MTA-t responds to the 200-OK message with the standard SIP ACK
message. At this point it is safe for MTA-t to start sending voice
payload packets to MTA-o1.
(27) ACK
ACK Host(mta-o.provider)
Via: SIP/2.0/UDP Host(mta-t.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
CSeq: 129 ACK
DCS Group Category: Informational - Expiration 8/31/02 84
DCS Architecture February 2002
10.11 Call-Transfer-Blind
MTA-o Proxy-o Proxy-t MTA-t
| | | |
|<-----------------call-in-progress------------------->|
| | | (1) REFER |
| | (2) REFER |<------------------|
| (3) REFER |<--------------| |
|<-----------------| | |
| |
| | Proxy-f MTA-f
| (4) INVITE | | |
|----------------->| (5) INVITE | |
| |-------------->| (6) INVITE |
| | |------------------>|
| | | (7) 183 SDP |
| | (8) 183 SDP |<------------------|
| (9) 183 SDP |<--------------| :
|<-----------------| : :
: : : (10) 200 OK |
: : (11) 200 OK |<------------------|
| (12) 200 OK |<--------------| |
|<-----------------| | |
| |
| | Proxy-t MTA-t
| (13) 200 OK | | |
|----------------->| (14) 200 OK | |
| |-------------->| (15) 200 OK |
| | (16) ACK |------------------>|
|<-----------------------------------------------------|
| | (17) BYE | |
|----------------------------------------------------->|
| | (18) 200 OK | |
|<-----------------------------------------------------|
| |
The Call Transfer service is triggered by the user by methods beyond
the scope of this specification. Described in this section is a
transfer service common known as "blind transfer" where the party
initiating the transfer (MTA-t in this example) is not informed of
the success or failure of the transfer operation. The alternative,
commonly known as "consultative transfer" is described later.
DCS Group Category: Informational - Expiration 8/31/02 85
DCS Architecture February 2002
For this example, consider an existing call initiated by MTA-o, with
the following call identification:
MTA-t state for call from MTA-o to MTA-t
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Contact: sip:Host(mta-o.provider)
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
Dcs-Billing-Info: Host(rks-o.provider)/04FA37<5123-0123-4567-
8900/212-555-1111/212-555-2222>
Dcs-Billing-ID: Host(dp-o.provider):36123E5C:0152
When MTA-t desires to transfer the existing call, it determines the
forwarding number (in this example 555-3333) and issues a REFER
message to MTA-o. REFER is the same as a regular INVITE but includes
an additional "Refer-to:" header and "Referred-by:" header. The
"Refer-to:" header identifies the number to which the call needs to
be forwarded, while the "Referred-by:" header identifies the
existing call leg at MTA-o. The following message is sent to MTA-
t's Proxy, Proxy-t.
(1) REFER:
REFER sip: Host(mta-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-t.provider)
Supported: 100rel, state
Refer-to: tel:555-3333
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
Remote-Party-ID: John Smith <tel:555-2222>
Anonymity: off
From: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
To: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 8001 INVITE
Referred-by: sip:B64(SHA-1(555-2222; time=36123E5B;
seq=73))@localhost
When the REFER is received at Proxy-t, it first verifies MTA-t has
subscribed to Call Forwarding service. If so, it decrypts the State
information to determine the local gate location and identification.
Proxy-t queries the gate to obtain the call's billing information.
DCS Group Category: Informational - Expiration 8/31/02 86
DCS Architecture February 2002
Proxy-t inserts billing information to indicate that the user
associated with the number 212-555-2222 will pay for the new call
segment. Proxy-t extracts the call routing from the Dcs-state
information, and then forwards the message to Proxy-o.
(2) REFER:
REFER sip: Host(dp-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(dp-t.provider)
Via: SIP/2.0/UDP Host(mta-t.provider)
Supported: 100rel, state
Proxy-Require: dcs
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124;
orig-dest=tel:+1-212-555-2222; num-redirects=0
Refer-to: tel:+1-212-555-3333? Dcs-Billing-Info= Host(rks-
o.provider)<5123-0123-4567-8900/212-555-1111/212-555-
2222> & Dcs-Billing-Info= Host(rks-t.provider)<4278-
9865-8765-9000/212-555-2222/212-555-3333> & Dcs-
Billing-ID= Host(dp-o.provider): 36123E5C:0152
Remote-Party-ID: John Smith <tel:+1-212-555-2222>
From: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
To: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 8001 INVITE
Referred-by: sip:B64(SHA-1(555-2222; time=36123E5B;
seq=73))@localhost
Proxy-o forwards the REFER message to MTA-o after encrypting the
<Dcs-Billing-Info, Dcs-Billing-ID> headers.
(3) REFER:
REFER sip: 555-1111@Host(mta-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(dp-o.provider), {via="Host(dp-
t.provider); branch=1"; via=Host(mta-t.provider)}K
Supported: 100rel, state
Refer-to: sip:{type=transfer; dest=tel:+1-212-555-3333;
billing-id=Host(dp-o.provider): 36123E5C:0152;
expires=<timestamp>; billing-info=Host(rks-
o.provider)<5123-0123-4567-8900/212-555-1111/212-555-
2222>; billing-info=Host(rks-t.provider)<4278-9865-
8765-9000/212-555-2222/212-555-3333>; orig-dest=tel:+1-
212-555-2222; redirected-by=tel:+1-212-555-2222; num-
redirects=1}K@Host(dp-o.provider);user=private
From: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
To: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 8001 INVITE
Referred-by: sip:B64(SHA-1(555-2222; time=36123E5B;
seq=73))@localhost
DCS Group Category: Informational - Expiration 8/31/02 87
DCS Architecture February 2002
After processing the REFER, MTA-o issues a INVITE to MTA-f. In
addition to the standard headers carried in an INVITE message, the
encrypted {Dcs-Billing-INFO, Dcs-Billing-ID} fields received in the
REFER message are copied into the INVITE message. These fields
indicate that the user associated with the 212-555-2222 number will
be charged for the second call leg.
(4) INVITE:
INVITE sip:{type=transfer; dest=tel:+1-212-555-3333; billing-
id=Host(dp-o.provider): 36123E5C:0152;
expires=<timestamp>; billing-info=Host(rks-
o.provider)<5123-0123-4567-8900/212-555-1111/212-555-
2222>; billing-info=Host(rks-t.provider)<4278-9865-
8765-9000/212-555-2222/212-555-3333>; orig-dest=tel:+1-
212-555-2222; redirected-by=tel:+1-212-555-2222; num-
redirects=1}K@Host(dp-o.provider);user=private SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
Remote-Party-ID: John Doe <tel:555-1111>
Anonymity: Off
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E98;
seq=74))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E98; seq=75))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E98;seq=74))@localhost
Cseq: 129 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
When the Proxy-o receives the INVITE it first decrypts the header
information to find the real destination for the call. Proxy
compares the current time against the timestamp in the encrypted
string; if the request is too old, it is refused. It invokes the
call routing logic to determine which Proxy (Proxy-f) to which the
INVITE needs to be routed. It also embeds two Dcs-Billing-Info
headers in this message. The first one identifies the user
associated with the E.164 number 212-555-1111 as paying for the
initial call leg (212-555-1111/212-555-2222). This information was
derived from the customer account information for the caller during
DCS Group Category: Informational - Expiration 8/31/02 88
DCS Architecture February 2002
the first call attempt. The second Dcs-Billing-Info header
identifies the user associated with the E.164 number 212-555-2222 as
paying for the second call leg (212-555-2222/212-555-3333), and was
provided by Proxy-t in the REFER message.
(5) INVITE:
INVITE sip: +1-212-555-3333;rn=+1-212-265-3333;
npdi=yes@Host(dp-f);user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-o.provider); branch=1;
Via: SIP/2.0/UDP Host(mta-o.provider);
Supported: 100rel, state
Require: state
Proxy-Require: dcs, state
Remote-Party-ID: John Doe <tel:+1-212-555-1111>
Anonymity: Off
Dcs-Gate: Host(cmts-o.provider):3612/17S30124/37FA1948
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/212-
555-1111/212-555-2222>
Dcs-Billing-Info: Host(rks-t.provider)<4278-9865-8765-9000/212-
555-2222/212-555-3333>
Dcs-Billing-ID: Host(dp-o.provider):36123E5C:0152
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E98;
seq=74))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E98; seq=75))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E98;seq=74))@localhost
Cseq: 129 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Upon receiving this INVITE, Proxy-f queries the directory server to
determine the IP address (MTA-f) associated with 212-555-3333. It
then forwards the INVITE message to MTA-f, after stripping off all
of the billing fields, and adding the encrypted state information.
This is identical to the basic call flow shown in Section 10.1, and
is not repeated here.
Upon receipt of the 200-OK message, MTA-o sends the final response
of the REFER, a 200-OK, to MTA-t. This message is routed through
DCS Group Category: Informational - Expiration 8/31/02 89
DCS Architecture February 2002
the Proxy Proxy-o, Proxy-t, and then delivered to MTA-t. MTA-t
responds directly with an ACK. Proxy-t is now done; MTA-o sends the
BYE message, which follows immediately.
(13) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(dp-o.provider), {via="Host(dp-
t.provider); branch=1"; via=Host(mta-t.provider)}K
State: Host(dp-o.provider); state="{gate= Host(cmts-
o.provider): 3612/17S30124, nexthop=sip:+1-212-555-
2222;rn=+1-212-234-2222@Host(DP-t), state="Host(dp-
t.provider); nexthop=sip:Host(dp-o.provider);
gate=Host(cmts-t.provider):4321/31S14621; orig-
dest=tel:+1-212-555-1111; num-redirects=0"}K"
From: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
To: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 8001 REFER
Proxy-o restores the encrypted Via headers, and forwards the OK to
topmost Via - Proxy-t.
(14) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(dp-t.provider)
Via: SIP/2.0/UDP Host(mta-t.provider)
From: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
To: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 8001 REFER
Proxy-tforwards the 200-OK to MTA-t.
(15) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-t.provider)
From: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
To: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 8001 REFER
MTA-t responds with an ACK message.
(16) ACK:
ACK sip:Host(mta-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-t.provider)
From: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
To: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
DCS Group Category: Informational - Expiration 8/31/02 90
DCS Architecture February 2002
Cseq: 8001 ACK
(17) BYE:
BYE sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 BYE
Upon receipt of the BYE message, MTA-t releases all network
resources that have been used for this call. MTA-t sends the
following 200-OK message to MTA-o.
(18) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 BYE
DCS Group Category: Informational - Expiration 8/31/02 91
DCS Architecture February 2002
10.12 Call-Transfer-Consultative
Call Transfer with Consultation is triggered by the user by methods
beyond the scope of this specification. It consists of two distinct
phases: first placing the existing call on hold and placing a new
call to another destination (the consultation), and secondly
transfering the first call to the second destination (the transfer).
For this example, consider an existing call initiated by MTA-t1 to
MTA-o. The call identification information at MTA-o is as follows:
MTA-o state for call from MTA-t1 to MTA-o
From: sip:B64(SHA-1(555-2222;time=36124033;seq=72))@localhost
To: tel:555-1111
Call-ID: B64(SHA-1(555-2222;time=36124033;seq=72))@localhost
Contact: sip: Host(mta-t1.provider)
Remote-Party-ID: tel:+1-212-555-2222
State: Host(dp-o.provider); state="{nexthop=sip:Host(dp-
t1.provider); gate=Host(cmts-o.provider):3612/17S30124;
state="Host(dp-t1.provider); nexthop=sip:555-
2222@Host(mta-t1.provider); gate=Host(cmts-
t1.provider):4321/31S14621; orig-dest=tel:+1-212-555-
1111; num-redirects=0"}K"
Dcs-Billing-Info: Host(rks-t1.provider)<4278-9865-8765-
9000/212-555-2222/212-555-1111>
Dcs-Billing-ID: Host(dp-t1.provider):36124033:0381
MTA-o places this call on hold and determines the destination for
consultation. MTA-o initiates a second call to the consultation
endpoint, MTA-t2, as shown in the figure below.
DCS Group Category: Informational - Expiration 8/31/02 92
DCS Architecture February 2002
MTA-o Proxy-o Proxy-t2 MTA-t1 MTA-t2
| (1) INVITE(Hold)| | | |
|------------------------------------------>| |
| (2) 200 OK | | | |
|<------------------------------------------| |
| (3) ACK | | | |
|------------------------------------------>| |
| | | | |
| (4) INVITE | | | |
|----------------->| (5) INVITE | | |
| |-------------->| (6) INVITE |
| | |------------------>|
| | | (7) 183 SDP |
| | (8) 183 SDP |<------------------|
| (9) 183 SDP |<--------------| | |
|<-----------------| (10) PRACK | | |
|----------------------------------------------------->|
| | (11) 200 OK | |
|<-----------------------------------------------------|
| | (12) COMET | |
|----------------------------------------------------->|
| | (13) 200 OK | |
|<-----------------------------------------------------|
| | | (14) 180 Ringing |
| |(15)180Ringing |<------------------|
| (16)180 Ringing |<--------------| |
|<-----------------| (17) PRACK | |
|----------------------------------------------------->|
| | (18) 200 OK | |
|<-----------------------------------------------------|
| | | |
| | | (19) 200 OK |
| | (20) 200 OK |<------------------|
| (21) 200 OK |<--------------| |
|<-----------------| (22) ACK | |
|----------------------------------------------------->|
| | | |
Signaling messages (1) to (3), placing the first call on hold, are
identical to those used in Call Waiting (see Section 10.10), and are
not reproduced here.
DCS Group Category: Informational - Expiration 8/31/02 93
DCS Architecture February 2002
Signaling messages (4) to (22), placing the second call, are
identical to those for a basic call flow (see Section 10.1), and are
not reproduced here. For this example, assume the Call-ID was
B64(SHA-1(555-1111;time=36124125;seq=23))@localhost.
State at MTA-o for call from MTA-o to MTA-t2
From: sip:B64(SHA-1(555-1111;time=36124125;seq=23))@localhost
To: tel:555-3333
Call-ID: B64(SHA-1(555-1111;time=36124125;seq=23))@localhost
Contact: sip: Host(mta-t2.provider)
Remote-Party-ID: tel:+1-212-555-3333
State: Host(dp-o.provider); state="{gate= Host(cmts-
o.provider): 3612/3S10782, nexthop=sip:+1-212-555-
3333;rn=+1-212-256-3333;npdi=yes@Host(dp-t2.provider),
state="Host(dp- t2.provider);
nexthop=sip:555-3333@Host(mta-t2.provider);
gate=Host(cmts- t2.provider):4321/31S14621;
orig-dest=tel:+1-212-555-1111; num-redirects=0"}K"
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/212-
555-1111/212-555-3333>
Dcs-Billing-ID: Host(dp-o.provider):3612E5C:0152
After some period of consultation, MTA-o initiates a transfer of the
call from MTA-t1 to the new destination, MTA-t2. This involves
placing the second call on hold (message sequence described
earlier), and sending a REFER message to MTA-t2, giving it the
information about the call with MTA-t1 in the REFER-By header. The
INVITE message, since it changes parties involved in the call, is
routed through the proxies. The sequence is shown in the following
figure, and detailed below.
DCS Group Category: Informational - Expiration 8/31/02 94
DCS Architecture February 2002
MTA-o MTA-t1 Proxy-o Proxy-t2 MTA-t2
| (1) REFER | | |
|----------------->| (2) REFER | |
| | |-------------->| (3) REFER |
| | | |------------------>|
| | | |
| | Proxy-t1 | (4) INVITE |
| | | (5)INVITE |<------------------|
| |(6)INVITE|<--------------| |
| |<--------| | |
| | (7)SDP | | |
| |-------->| (8) SDP | |
| | |-------------->| (9) SDP |
| | | (10) PRACK |------------------>|
| |<--------------------------------------------|
| | | (11) 200 OK | |
| |-------------------------------------------->|
| | | (12) COMET | |
| |<--------------------------------------------|
| | | (13) 200 OK | |
| |-------------------------------------------->|
| |(14)200 | | |
| |-------->| (15) 200 OK | |
| | |-------------->| (16) 200 OK |
| | | (17) ACK |------------------>|
| |<--------------------------------------------|
| | | | |
| | Proxy-o | (17) 200 OK |
| | | (18)200 OK |<------------------|
| (19) 200 OK |<--------------| |
|<-----------------| | |
| | | (20) BYE | |
|----------------------------------------------------->|
| | | (21) 200 OK | |
|<-----------------------------------------------------|
|(22)BYE | | | |
|------->| | | |
|(23)200 | | | |
|<-------| | | |
DCS Group Category: Informational - Expiration 8/31/02 95
DCS Architecture February 2002
After placing the second call on hold, MTA-o initiates a transfer by
sending a REFER to MTA-t2, routed through the proxies.
(1) REFER:
REFER sip: Host(mta-t2.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
Remote-Party-ID: John Doe <tel:555-1111>
Anonymity: off
Refer-to: tel:+1-212-555-2222 ? Call-ID=B64(SHA-1(555-
1111;time=36124033;seq=72) & Referred-by=tel:555-1111
& State= Host(dp-o.provider);state="{nexthop=sip:Host(
dp-t1.provider); gate=Host(cmts-
o.provider):3612/17S30124; state="Host(dp-t1.provider);
nexthop=sip:555-2222@Host(mta-t1.provider);
gate=Host(cmts-t1.provider):4321/31S14621; orig-
dest=tel:+1-212-555-1111; num-redirects=0"}K"
State: Host(dp-o.provider); state="{gate= Host(cmts-
o.provider): 3612/3S10782, nexthop=sip:+1-212-555-
3333;rn=+1-212-256-3333;npdi=yes@Host(dp-t2.provider),
state="Host(dp- t2.provider);
nexthop=sip:555-3333@Host(mta-t2.provider);
gate=Host(cmts- t2.provider):4321/31S14621;
orig-dest=tel:+1-212-555-1111; num-redirects=0"}K"
From: sip:B64(SHA-1(555-1111;time=36124125;seq=23))@localhost
To: tel:555-3333
Call-ID: B64(SHA-1(555-1111;time=36124125;seq=23))@localhost
CSeq: 133 REFER
Referred-by: sip:B64(SHA-1(555-1111;time=36124125;
seq=23))@localhost
When the REFER is received at Proxy-o, it first verifies MTA-o has
subscribed to Call Transfer service. If so, it decrypts the State
information in the Refer-to header to determine the local gate
location and identification. Proxy-o queries the gate to obtain the
transferred call's original billing information. Proxy-o inserts
billing information to indicate that the user associated with the
number 212-555-1111 will pay for the new call segment. Proxy-o
extracts the call routing from the Dcs-state information, and then
forwards the message to Proxy-t2.
(2) REFER:
REFER sip: Host(dp-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(dp-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
Proxy-Require: dcs
State: Host(dp-t2.provider); nexthop=sip:555-3333@Host(mta-
t2.provider); gate=Host(cmts-
t2.provider):4321/31S14621; orig-dest=tel:+1-212-555-
1111; num-redirects=0
Refer-to: tel:+1-212-555-2222? Call-ID=B64(SHA-1(555-
1111;time=36124033;seq=72) & Referred-by=tel:555-1111
DCS Group Category: Informational - Expiration 8/31/02 96
DCS Architecture February 2002
& Dcs-Billing-Info= Host(rks-t1.provider)<4278-9865-
8765-9000/212-555-2222/212-555-1111> & Dcs-Billing-
Info= Host(rks-t2.provider)<5123-0123-4567-8900/212-
555-1111/212-555-3333> & Dcs-Billing-ID= Host(dp-
o.provider): 36123E5C:0152
Remote-Party-ID: John Smith <tel:+1-212-555-2222>
From: sip:B64(SHA-1(555-1111;time=36124125;seq=23))@localhost
To: tel:555-3333
Call-ID: B64(SHA-1(555-1111;time=36124125;seq=23))@localhost
CSeq: 133 REFER
Referred-by: sip:B64(SHA-1(555-1111;time=36124125;
seq=23))@localhost
Proxy-t2 forwards the REFER message to MTA-t2 after encrypting the
destination of the transfer, and the Dcs-Billing, Dcs-Billing-ID
headers.
(3) REFER:
REFER sip: 555-3333@Host(mta-t2.provider) SIP/2.0
Via: SIP/2.0/UDP Host(dp-t2.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
Supported: 100rel, state
Refer-to: sip:{type=transfer; dest=tel:+1-212-555-2222;
billing-id=Host(dp-o.provider): 36123E5C:0152;
expires=<timestamp>; billing-info= Host(rks-
t1.provider)<4278-9865-8765-9000/212-555-2222/212-555-
1111> ; billing-info= Host(rks-t2.provider)<5123-0123-
4567-8900/212-555-1111/212-555-3333>}K@Host(dp-
t2.provider);user=private ? Call-ID=B64(SHA-1(555-
1111;time=36124033;seq=72) & Referred-by=tel:555-1111
Remote-Party-ID: John Smith <tel:+1-212-555-2222>
From: sip:B64(SHA-1(555-1111;time=36124125;seq=23))@localhost
To: tel:555-3333
Call-ID: B64(SHA-1(555-1111;time=36124125;seq=23))@localhost
CSeq: 133 INVITE
Referred-by: sip:B64(SHA-1(555-1111;time=36124125;
seq=23))@localhost
After processing the REFER, MTA-t2 issues a INVITE to MTA-t1. In
addition to the standard headers carried in an INVITE message, the
encrypted {Dcs-Billing, Dcs-Billing-ID} fields received in the REFER
message are copied into the Request-URI of the INVITE message. These
fields indicate the destination, and that the user associated with
the 212-555-1111 number will be charged for the second call leg.
(4) INVITE:
INVITE sip:{type=transfer; dest=tel:+1-212-555-2222; billing-
id=Host(dp-o.provider): 36123E5C:0152;
expires=<timestamp>; billing-info= Host(rks-
t1.provider)<4278-9865-8765-9000/212-555-2222/212-555-
1111> ; billing-info= Host(rks-t2.provider)<5123-0123-
DCS Group Category: Informational - Expiration 8/31/02 97
DCS Architecture February 2002
4567-8900/212-555-1111/212-555-3333>}K@Host(dp-
t2.provider);user=private SIP/2.0
Via: SIP/2.0/UDP Host(mta-t2.provider)
Supported: 100rel, state
Remote-Party-ID: John Smith <tel:555-3333>
Anonymity: Off
From: "Alien Blaster" <sip:B64(SHA-1(555-3333; time=36124172;
seq=74))@localhost>
To: sip:B64(SHA-1(555-3333; time=36124172; seq=75))@localhost
Call-ID: B64(SHA-1(555-1111;time=36124033;seq=72)@localhost
Cseq: 129 INVITE
Referred-by: tel:555-1111
Contact: sip:Host(mta-t2.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-t2.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
When the Proxy-t2 receives the INVITE it first decrypts the header
information to find the real destination for the call. Proxy
compares the current time against the timestamp in the encrypted
string; if the request is too old, it is refused. It invokes the
call routing logic to determine which Proxy (Proxy-t1) to which the
INVITE needs to be routed. It also embeds two Dcs-Billing-Info
headers in this message. The first one identifies the user
associated with the E.164 number 212-555-2222 as paying for the
initial call leg (212-555-2222/212-555-1111). This information was
derived from the customer account information for the caller during
the first call attempt. The second Dcs-Billing-Info header
identifies the user associated with the E.164 number 212-555-1111 as
paying for the second call leg (212-555-1111/212-555-3333), and was
provided by Proxy-o in the REFER message.
(5) INVITE:
INVITE sip: +1-212-555-2222;rn=+1-212-265-2222;
npdi=yes@Host(dp-t1);user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-t2.provider); branch=1;
Via: SIP/2.0/UDP Host(mta-t2.provider);
Supported: 100rel, state
Require: state
Proxy-Require: dcs, state
DCS Group Category: Informational - Expiration 8/31/02 98
DCS Architecture February 2002
Remote-Party-ID: John Smith <tel:+1-212-555-3333>
Anonymity: Off
Dcs-Gate: Host(cmts-t2.provider):3612/17S30124/37FA1948
Dcs-Billing-Info: Host(rks-t1.provider)<4278-9865-8765-
9000/212-555-2222/212-555-1111>
Dcs-Billing-Info: Host(rks-t2.provider)<5123-0123-4567-
8900/212-555-1111/212-555-3333>
Dcs-Billing-ID: Host(dp-o.provider):36123E5C:0152
From: "Alien Blaster" <sip:B64(SHA-1(555-3333; time=36124172;
seq=74))@localhost>
To: sip:B64(SHA-1(555-3333; time=36124172; seq=75))@localhost
Call-ID: B64(SHA-1(555-1111;time=36124033;seq=72)@localhost
Cseq: 129 INVITE
Reffered-By: tel:555-1111
Contact: sip:Host(mta-t2.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Upon receiving this INVITE, Proxy-t1 queries the directory server to
determine the IP address (MTA-t1) associated with 212-555-2222. It
then forwards the INVITE message to MTA-t1, after stripping off all
of the billing fields, and adding the encrypted state information.
MTA-t1 recognizes the Call-ID matching an existing call, and matches
the value of the Reffered-By: header to the From/To of that call.
Since they match, the call is allowed to proceed, with the 183-
Session-Progress, receiving PRACK, COMET, etc. These messages are
identical to the basic call flow shown in Section 10.1, and are not
repeated here.
Upon receipt of the 200-OK response from MTA-t1, MTA-t2 sends the
final response of the REFER by sending a 200-OK to MTA-o. This
message is routed through the Proxy Proxy-t2, Proxy-o, and then
delivered to MTA-o. MTA-o responds directly with an ACK. Proxy-o
is now done, and MTA-o sends a BYE message to terminate the call leg
from MTA-o to MTA-t2, and a BYE message to terminate the call leg
from MTA-o to MTA-t1.
DCS Group Category: Informational - Expiration 8/31/02 99
DCS Architecture February 2002
10.13 Three-Way-Calling (with Network Bridge)
Three-way calling is a fairly complex consumer service that allows a
subscriber to simultaneously talk to two parties, and for those two
parties to hear each other. It is often thought of as an ad-hoc
conference bridge. Usage of the service proceeds as follows. The
customer has an active call, either one initiated or received. The
customer then does a hookflash, which places the existing call on
hold and presents a dialtone. The user then dials the a second
number, and connects to that party. A hookflash at this point
creates a 3-way call, bridging the two calls together. Note the
distinction between three-way calling and call waiting (where the
two calls are alternately placed on hold and connected) lies in the
fact that the subscriber initiated the second call; if the second
call was an incoming call then the call-waiting service would be
active.
The desired state during the three-way-call is three separate call
legs, from each participant to the bridge server. If the
participants initiate the calls, then they all have the same Call-
ID, which tells the bridge to mix them together. If the bridge
initiates the connections, there is no necessity for a common Call-
ID. Multiple methods exist using combinations of REFER methods and
headers to achieve the desired connections. One way involves the
subscriber establishing a connection to a bridge element, then
transferring both of the existing calls to the bridge. Another
method involves the subscriber asking the bridge to handle
redirecting the existing calls to itself. The latter involves fewer
signaling messages, and is preferred over the former. There is, of
course, a third option - that the conference bridging function is
done within the MTA and the network sees it as two separate
simultaneous calls. As this consumes double the access network
bandwidth, it is discouraged.
Initially a single call is active. For purposes of this example,
consider that call to have been a call initiated by MTA-t1 to MTA-o.
The call identification information at MTA-o is as follows:
MTA-o state for call from MTA-t1 to MTA-o
From: sip:B64(SHA-1(555-2222;time=36124033;seq=72))@localhost
To: tel:555-1111
Call-ID: B64(SHA-1(555-2222;time=36124033;seq=72))@localhost
DCS Group Category: Informational - Expiration 8/31/02 100
DCS Architecture February 2002
Contact: sip: Host(mta-t1.provider)
Remote-Party-ID: tel:+1-212-555-2222
State: Host(dp-o.provider); state="{nexthop=sip:Host(dp-
t.provider); gate=Host(cmts-o.provider):3612/17S30124;
state="Host(dp-t.provider); nexthop=sip:555-
2222@Host(mta-t1.provider); gate=Host(cmts-
t.provider):4321/31S14621; orig-dest=tel:+1-212-555-
1111; num-redirects=0"}K"
Dcs-Billing-Info: Host(rks-t1.provider)<4278-9865-8765-
9000/212-555-2222/212-555-1111>
Dcs-Billing-ID: Host(dp-t1.provider):36124033:0381
MTA-o observes a hookflash and places this call on hold, issues a
dialtone, and collects digits for a second call (212-555-3333).
This sequence is shown in Section 10.10, resulting in the first call
being held and a conversation active to the second destination.
For this example, assume the second call is identified as follows:
State at MTA-o for call from MTA-o to MTA-t2
From: sip:B64(SHA-1(555-1111;time=36124125;seq=23))@localhost
To: tel:555-3333
Call-ID: B64(SHA-1(555-1111;time=36124125;seq=23))@localhost
Contact: sip: Host(mta-t2.provider)
Remote-Party-ID: tel:+1-212-555-3333
State: Host(dp-o.provider); state="{gate= Host(cmts-
o.provider): 3612/3S10782, nexthop=sip:+1-212-555-
3333;rn=+1-212-256-3333@Host(DP-t), state="Host(dp-
t.provider); nexthop=sip:555-3333@Host(mta-t.provider);
gate=Host(cmts-t.provider):4321/31S14621; orig-
dest=tel:+1-212-555-1111; num-redirects=0"}K"
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/212-
555-1111/212-555-3333>
Dcs-Billing-ID: Host(dp-o.provider):3612E5C:0152
The three-way-calling method described in this appendix asks the
bridge to redirect the existing calls via an INVITE(Refer). The
bridge therefore is in control of managing the endpoints, and knows
the proper media streams for mixing, even though they don't have a
common Call-ID.
DCS Group Category: Informational - Expiration 8/31/02 101
DCS Architecture February 2002
MTA-o MTA-t1 Proxy-o Proxy-b MTA-t2
| | (1) INVITE(Hold) |
|----------------------------------------------------->|
| | (2) 200 OK | |
|----------------------------------------------------->|
| | (3) ACK | |
|----------------------------------------------------->|
| | |
| (4) REFER | | Bridge
|----------------->| (5) REFER | |
| | |-------------->| (6) REFER |
| | | |------------------>|
| | | | (7) 183 SDP |
| | | (8) 183 SDP |<------------------|
| (9) 183 SDP |<--------------| |
|<-----------------| (10) PRACK | |
|----------------------------------------------------->|
| | | (11) 200 OK | |
|<-----------------------------------------------------|
| | | (12) COMET | |
|----------------------------------------------------->|
| | | (13) 200 OK | |
|<-----------------------------------------------------|
| | | | (14) 200 OK |
| | | (15) 200 OK |<------------------|
| (16) 200 OK |<--------------| |
|<-----------------| (17) ACK | |
|----------------------------------------------------->|
| | | | |
| | | | (18) INVITE |
| | | (19)INVITE |<------------------|
| (20)INVITE|<--------------| |
| |<--------| | |
| |(21)SDP | | |
| |-------->| (22) SDP | |
| | |-------------->| (23) SDP |
| | | (24) PRACK |------------------>|
| |<--------------------------------------------|
| | | (25) 200 OK | |
| |-------------------------------------------->|
| | | (26) COMET | |
DCS Group Category: Informational - Expiration 8/31/02 102
DCS Architecture February 2002
| |<--------------------------------------------|
| | | (27) 200 OK | |
| |-------------------------------------------->|
| |(28)200 | | |
| |-------->| (29) 200 OK | |
| | |-------------->| (30) 200 OK |
| | | (31) ACK |------------------>|
|(32)BYE |<--------------------------------------------|
|<-------| | | |
|(33)200 | | | |
|------->| | | |
Messages (1) to (3), for putting an existing call on hold, are
identical to those used in Call Waiting (see Section 10.10).
In response to the hook-flash, MTA also issues an INVITE to a bridge
with a new call ID. The identity of the destination is given via
the service name "bridge," which is a pre-defined service name in
DCS.
(4) REFER:
REFER sip: bridge@Host(dp-o) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
Remote-Party-ID: John Doe <tel:555-1111>
Anonymity: Off
Refer-To: tel:+1-212-555-2222 ? Call-ID=B64(SHA-1(555-
2222;time=36124033;seq=72))@localhost & Reffered-By
=tel:555-1111 & State= Host(dp-o.provider);
state="{nexthop=sip:Host(dp-t.provider);
gate=Host(cmts-o.provider):3612/17S30124;
state="Host(dp-t.provider); nexthop=sip:555-
2222@Host(mta-t1.provider); gate=Host(cmts-
t.provider):4321/31S14621; orig-dest=tel:+1-212-555-
1111; num-redirects=0"}K"
Refer-To: tel:+1-222-555-3333 ? Call-ID=B64(SHA-1(555-
1111;time=36124125;seq=23))@localhost & Reffered-By
=B64(SHA-1(555-1111;time-
36124125;seq=23))@localhost & State= Host(dp-
o.provider); state="{gate= Host(cmts-o.provider):
3612/3S10782, nexthop=sip:+1-212-555-3333;rn=+1-212-
256-3333@Host(DP-t), state="Host(dp-t.provider);
nexthop=sip:555-3333@Host(mta-t.provider);
gate=Host(cmts-t.provider):4321/31S14621; orig-
dest=tel:+1-212-555-1111; num-redirects=0"}K"
From: sip:B64(SHA-1(555-1111; time=36124135;seq=24))@localhost
To: sip: bridge@Host(dp-o.provider)
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
Contact: sip:Host(mta-o.provider)
Cseq: 131 INVITE
Content-Type: application/sdp
Content-length: (.)
v=0
DCS Group Category: Informational - Expiration 8/31/02 103
DCS Architecture February 2002
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3460 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Proxy-o resolves the "bridge service name" to an available bridge
(mcu41@Host(dp-b.provider) in this example), and forwards the INVITE
to the associated Proxy (Proxy-b). In general, bridges will be
available locally at Proxy-o, but this example demonstrates the
messages exchanged if the bridge is remote. In general, bridges
will be network services and located within the trusted domain of
the network. However, they may also be provided by others. This
example call flow diagram shows the latter case, where the bridge is
outside the trusted domain of the service provider.
If the bridge is a trusted network element, the Bridge (for
signaling purposes) would be functionally equivalent to a CMS, and
use the same message set as is used between CMSs. In the diagram
above, this would appear as if the lines Proxy-b and BRIDGE were
merged together.
Proxy-o decrypts the state header values attached to the Refer-To
headers, extracts the billing information for each of the previous
call legs, and expands this information into the Dcs-Billing-Info
values
(5) REFER:
REFER sip:mcu41@Host(dp-b.provider) SIP/2.0
Via: SIP/2.0/UDP Host(dp-o.provider)
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
Proxy-Require: dcs, state
Require: state
Remote-Party-ID: John Doe <tel:+1-212-555-1111>
Anonymity: Off
Dcs-Gate: Host(cmts-o.provider):3612/5S12045/9142E7A1
Dcs-Billing-Info: Host(rks-o.provider)<5123-4567-8900/212-555-
1111/mcu41@Host(dp-b.provider)/bridge-3>
Dcs-Billing-ID: Host(dp-o.provider):36124135:92
Refer-To: tel:+1-212-555-2222 ? CallID= B64(SHA-1(555-
2222;time=36124033;seq=72))@localhost & Dcs-Billing-
Info= Host(rks-t1.provider)<4278-9865-8765-9000/212-
555-2222/212-555-1111> & Dcs-Billing-Info= Host(rks-
o.provider)<5123-4567-8900/212-555-1111/mcu41@Host(dp-
b.provider)> & Dcs-Billing-ID= Host(dp-
t1.provider):36124033:0381 & Reffered-By=tel:555-1111
DCS Group Category: Informational - Expiration 8/31/02 104
DCS Architecture February 2002
Refer-to: tel:+1-212-555-3333 ? CallID= B64(SHA-1(555-
1111;time=36124125;seq=23))@localhost & Dcs-Billing-
Info= Host(rks-o.provider)/<5123-4567-8900/212-555-
1111/212-555-3333> & Dcs-Billing-Info= Host(rks-
o.provider)<5123-4567-8900/212-555-1111/mcu41@Host(dp-
b.provider)> & Dcs-Billing-ID= Host(dp-
o.provider):36123E5C:0152 & Reffered-By:B64(SHA-1(555-
1111;time-36124125;seq=23))@localhost
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124
From: sip:B64(SHA-1(555-1111; time=36124135;seq=24))@localhost
To: sip: bridge@Host(dp-o.provider)
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
Contact: sip:Host(mta-o.provider)
Cseq: 131 INVITE
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
A=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3460 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Proxy-b encrypts the various fields into two Refer-To: headers,
caches the Via headers, and passes the message to the bridge.
(6) REFER:
REFER sip:mcu41.provider SIP/2.0
Via: SIP/2.0/UDP Host(dp-b.provider), {via=Host(dp-o.provider);
via=Host(mta-o.provider)}K
Supported: 100rel, state
Require: state
Remote-Party-ID: John Doe <tel:+1-212-555-1111>
Dcs-Gate: 27S6028
Refer-To: sip:{type=transfer; dest=+1-212-555-2222; Billing-
info=Host(dp-t1.provider):36124033:0381; <timestamp>;
Billing-info=Host(rks-t1.provider)<4278-9865-8765-
9000/212-555-2222/212-555-1111>; Billing-id=Host(rks-
o.provider)<5123-4567-8900/212-555-
1111/mcu41.provider>}K@dp-b.provider;user=private ?
Call-ID= B64(SHA-1(555-2222;time=36124033;seq=72))
@localhost & Reffered-By=tel:555-1111
Refer-To: sip:{type=transfer; dest=+1-212-555-3333; billing-
id=Host(dp-o.provider):36123E5C:0152;
expires=<timestamp>; billing-info=Host(rks-
DCS Group Category: Informational - Expiration 8/31/02 105
DCS Architecture February 2002
o.provider)/<5123-4567-8900/212-555-1111/212-555-3333>;
billing-info=Host(rks-o.provider)<5123-4567-8900/212-
555-1111/mcu41.provider>}K@dp-b.provider; user=private
? Call-ID= B64(SHA-1(555-
1111;time=36124125;seq=23))@localhost & Reffered-By
:B64(SHA-1(555-1111;time-36124125;seq=23))
State: Host(dp-b.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-b.provider): 3612/27S6028;
via="Host(dp-o.provider);branch=1", via=Host(mta-
o.provider), state="Host(dp-o.provider);
nexthop=sip:555-1111@Host(mta-o.provider);
gate=Host(cmts-o.provider):3612/17S30124"}K"
From: sip:B64(SHA-1(555-1111; time=36124135;seq=24))@localhost
To: sip: bridge@Host(dp-o.provider)
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
Contact: sip:Host(mta-o.provider)
Cseq: 131 INVITE
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
A=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3460 RTP/AVP 0
a=X-pc-codecs:96
Bridge completes the call from MTA-o in a manner very similar to the
basic call flow of Section 10.1. Since a bridge doesn't need to
alert a human, it responds immediately with 200-OK when resources
are known to be available. Messages (7) through (17) are not
detailed in this section.
Bridge initiates two calls in parallel, one to each of the
participants listed in the Refer-To: headers. The Request URI in
the new INVITE message is the encrypted string received in the
Refer-To: header, the To: header is a generic string such as
"participant<n>" since the bridge has no knowledge of the identity
of the participants, and the Call-ID is the value from the Refer-To
header. Part of the message sequence for MTA-t1 (messages (18) to
(33)) is detailed here; messages (34) through (49) are identical and
not shown in the figure.
(18) INVITE (Refer-By):
INVITE sip:{type=transfer; dest=+1-212-555-2222; Billing-
info=Host(dp-t1.provider):36124033:0381; <timestamp>;
Billing-info=Host(rks-t1.provider)<4278-9865-8765-
DCS Group Category: Informational - Expiration 8/31/02 106
DCS Architecture February 2002
9000/212-555-2222/212-555-1111>; Billing-id=Host(rks-
o.provider)<5123-4567-8900/212-555-
1111/mcu41.provider>}K@dp-b.provider; user=private
SIP/2.0
Via: SIP/2.0/UDP Host(mcu41.provider)
Supported: 100rel, state
Remote-Party-ID: Bridge Service <sip:Host(mcu41.provider)>
Anonymity: URL, Name
From: sip:B64(SHA-1(bridge;time=36124135;seq=311))@localhost
To: sip: participant1@localhost
Call-ID: B64(SHA-1(555-2222;time=36124033;seq=72))@localhost
Contact: sip:Host(mcu41.provider)
Cseq: 128 INVITE
Refer-By:tel:555-1111
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mcu41.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3174 RTP/AVP 0
a=X-pc-Qos:mandatory sendrecv
a=X-pc-codecs:96
Proxy-b decodes the encrypted Request-URI to find the real
destination for this call. Proxy compares the current time against
the expiration time in the encrypted string; if the request is too
old it is refused. The call routing is determined from the
destination contained in the encrypted string, as is the billing
information for the call. Proxy-b sends the following INVITE
message to Proxy-t1:
(19) INVITE (Refer-By):
INVITE sip:+1-212-555-2222;rn=+1-212-234-2222;
npdi=yes@Host(dp-t1.provider);user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-b.provider)
Via: SIP/2.0/UDP Host(mcu41.provider)
Supported: 100rel, state
Require: state
Proxy-Require: dcs, state
Remote-Party-ID: Bridge Service <sip:Host(mcu41.provider)>
Anonymity: URL, Name
Dcs-Gate: Host(cmts-b.provider):3612/28S6029/079317A3
State: Host(dp-b.provider); nexthop=Host(mcu41.provider);
gate=Host(cmts-b)::3621/28S6029; orig-dest=tel:+1-212-
555-2222; num-redirects=0
DCS Group Category: Informational - Expiration 8/31/02 107
DCS Architecture February 2002
From: sip:B64(SHA-1(bridge;time=36124135;seq=311))@localhost
To: sip: participant1@localhost
Call-ID: B64(SHA-1(555-2222;time=36124033;seq=72))@localhost
Contact: sip:Host(mcu41.provider)
Cseq: 128 INVITE
Refer-By:tel:555-1111
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(bridge.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
a=qos:mandatory sendrecv
m=audio 3174 RTP/AVP 0
Proxy-t1 processes this exactly as a normal INVITE message, and
passes the message to MTA-t1.
(20) INVITE (Refer-By):
INVITE sip:555-2222@Host(mta-t1.provider) SIP/2.0
Via: SIP/2.0/UDP Host(dp-t1.provider), {via=Host(dp-
b.provider); via=Host(mcu41.provider)}K
Supported: 100rel, state
Require: state
Remote-Party-ID: <sip:{type=rem-id;dest=sip:Host(mcu41.
provider)}K@Host(dp-t1.provider); user=private>
Media-Authorization: 5S32740
State: Host(dp-t1.provider); state={nexthop=sip:Host(dp-b);
gate=Host(cmts-t1:3621/53S32740;state="Host(dp-
b.provider); nexthop=Host(mcu41.provider);
gate=Host(cmts-b)::3621/28S6029; orig-dest=tel:+1-212-
555-2222; num-redirects=0"}K
From: sip:B64(SHA-1(bridge;time=36124135;seq=311))@localhost
To: sip: participant1@localhost
Call-ID: B64(SHA-1(555-2222;time=36124033;seq=72))@localhost
Contact: sip:Host(mcu41.provider)
Cseq: 128 INVITE
Refer-By:tel:555-1111
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mcu41.provider)
b=AS:64
DCS Group Category: Informational - Expiration 8/31/02 108
DCS Architecture February 2002
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3174 RTP/AVP 0
a=X-pc-Qos:mandatory sendrecv
a=X-pc-codecs:96
MTA-t1 notes the Call-ID: header, and determines that it has a call
with that ID and that the Refer-By: header matches either the From:
or To: value for the call. This INVITE is therefore interpreted as
an update to that existing call. The provisional response (183-
Session-Progress) is sent (21) to the local Proxy, who restores the
encrypted Via: headers and sends it (22) to the originating Proxy,
who passes it (23) to the bridge. These messages are identical to
those of the basic call flow. The bridge responds with the PRACK
message (24), as in the basic call flow. The bridge then performs
the resource allocation and continues as in the basic call flow.
Upon receipt of the ACK message, MTA-t1 sends a BYE message to its
original caller. Note that this message has the From: and To:
headers reversed from the incoming INVITE originally received for
this call. If MTA-t1 had initiated the call to MTA-o, then the
From: and To: would match those in the initial INVITE.
(32) BYE:
BYE sip:Host(mta-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-t1.provider)
From: tel:555-1111
To: sip:B64(SHA-1(555-2222;time=36124033;seq=72))@localhost
Call-ID: B64(SHA-1(555-2222;time=36124033;seq=72))@localhost
Cseq: 129 BYE
Upon receipt of the BYE message, MTA-o sends the following 200-OK
message to MTA-t1.
(33) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-t1.provider)
From: tel:555-1111
To: sip:B64(SHA-1(555-2222;time=36124033;seq=72))@localhost
Call-ID: B64(SHA-1(555-2222;time=36124033;seq=72))@localhost
Cseq: 129 BYE
The sequence of messages (34)-(49) is identical, and performs the
same functions for the other leg of the three-way conference.
DCS Group Category: Informational - Expiration 8/31/02 109
DCS Architecture February 2002
10.14 Three-Way-Calling Hangup sequences
There are two distinct hangup sequences that need to be detailed:
hangup of a participant and hangup of the originator. The first
results in a basic call between the originator and the remaining
participant. The latter results in a hangup of all participants.
For both of the following detail call flows, consider the initial
state information to be the following:
MTA-o: Call from MTA-o to BRIDGE
From: sip:B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
To: sip:bridge@Host(dp-o.provider)
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
Contact: sip:Host(mcu41.provider)
State: Host(dp-o.provider); state="{gate= Host(cmts-
o.provider): 3612/12S52127, nexthop=sip: mcu41@Host(dp-
b), state="Host(dp-b.provider);
nexthop=sip:Host(mcu41.provider); gate=Host(cmts-
b.provider):4321/31S14621; orig-dest=sip:mcu41@Host(dp-
b); num-redirects=0"}K"
Dcs-Billing-Info: Host(rks-o.provider)/341FE8B<5123-0123-4567-
8900/212-555-1111/mcu41.provider/Bridge-3
MTA-t1: Call from BRIDGE to MTA-t1
From: sip:B64(SHA-1(bridge;time=36124135;seq=311))@localhost
To: sip: participant1@localhost
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24)) @localhost
Contact: sip:Host(mcu41.provider)
State: Host(dp-t1.provider); state="{nexthop=sip:Host(dp-
b.provider); gate=Host(cmts-t1.provider):
3612/12S52127; state="Host(dp-b.provider);
nexthop=sip:Host(mcu41.provider); gate=Host(cmts-
b.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
Dcs-Billing-Info: Host(rks-t1.provider)<4278-9865-8765-
9000/212-555-2222/212-555-1111>;Host(rks-
o.provider)<5123-4567-8900/212-555-2222/mcu41.provider>
MTA-t2: Call from BRIDGE to MTA-t2
From: sip:B64(SHA-1(bridge;time=36124135;seq=312)) @localhost
DCS Group Category: Informational - Expiration 8/31/02 110
DCS Architecture February 2002
To: sip: participant2@localhost
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24)) @localhost
Contact: sip:Host(mcu41.provider)
State: Host(dp-t2.provider); state="{nexthop=sip:Host(dp-
b.provider); gate=Host(cmts-t2.provider):
3612/13S52196; state="Host(dp-b.provider);
nexthop=sip:Host(mcu41.provider); gate=Host(cmts-
b.provider):3612/18S37224; orig-dest=tel:+1=212-555-
3333; num-redirects=0"}K"
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/212-
555-1111/212-555-3333>;Host(rks-o.provider)<5123-4567-
8900/212-555-3333/mcu41.provider>
Bridge: Call from MTA-o to BRIDGE
From: sip:B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
To: sip:bridge@Host(dp-o.provider)
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
Contact: sip:Host(mta-o.provider)
Remote-Party-ID: tel:+1-212-555-1111
State: Host(dp-b.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-b.provider):3612/15S30179;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
1111; num-redirects=0"}K"
Dcs-Billing-Info: Host(rks-o.provider)/341FE8B<5123-0123-4567-
8900/212-555-1111/mcu41.provider/Bridge-3
Bridge: Call from BRIDGE to MTA-t1
From: sip:B64(SHA-1(bridge;time=36124135;seq=311))@localhost
To: sip: participant1@localhost
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
Contact: sip:Host(mta-t1.provider)
State: Host(dp-b.provider); state="{gate= Host(cmts-
b.provider): 3612/17S30124, nexthop=sip:+1-212-555-
2222;rn=+1-212-234-2222@Host(DP-t1), state="Host(dp-
t1.provider); nexthop=sip:555-2222@Host(mta-
t1.provider); gate=Host(cmts-
t1.provider):4321/31S14621; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
Dcs-Billing-Info: Host(rks-t1.provider)<4278-9865-8765-
9000/212-555-2222/212-555-1111>;Host(rks-
o.provider)<5123-4567-8900/212-555-2222/mcu41.provider>
Bridge: Call from BRIDGE to MTA-t2
From: sip:B64(SHA-1(bridge;time=36124135;seq=312))@localhost
To: sip: participant2@localhost
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
Contact: sip:Host(mta-t2.provider)
State: Host(dp-b.provider); state="{gate= Host(cmts-
b.provider): 3612/18S37624, nexthop=sip:+1-212-555-
3333;rn=+1-212-234-3333@Host(DP-t2), state="Host(dp-
t2.provider); nexthop=sip:555-3333@Host(mta-
DCS Group Category: Informational - Expiration 8/31/02 111
DCS Architecture February 2002
t2.provider); gate=Host(cmts-
t2.provider):3621/13S52196; orig-dest=tel:+1-212-555-
3333; num-redirects=0"}K"
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/212-
555-1111/212-555-3333>;Host(rks-o.provider)<5123-4567-
8900/212-555-3333/mcu41.provider>
MTA-o MTA-t1 Proxy-o Proxy-b Bridge
| | | (1) BYE | |
| |-------------------------------------------->|
| | | (2) 200 OK | |
| |<--------------------------------------------|
| | | | |
| | | | (3) REFER |
| | | (4) REFER |<------------------|
| (5) REFER |<--------------| |
|<-----------------| | |
| (6) 200 OK | | |
|----------------->| (7) 200 OK | |
| | |-------------->| (8) 200 OK |
| | | (9) ACK |------------------>|
|<-----------------------------------------------------|
| | |
| | | Proxy-t2 MTA-t2
| | | | |
| (10) INVITE | | |
|----------------->| (11) INVITE | |
| | |-------------->| (12) INVITE |
| | | |------------------>|
| | | | (13) 183 SDP |
| | | (14) 183 SDP |<------------------|
| (15) 183 SDP |<--------------| |
|<-----------------| (16) PRACK | |
|----------------------------------------------------->|
| | | | |
For this example, consider MTA-t1 to drop out of the three-way
conference. MTA-t1 sends a BYE message to terminate its current
call.
(1) BYE
SIP/2.0 BYE Host(mcu41.provider)
Via: SIP/2..0/UDP Host(mta-t1.provider)
From: sip:B64(SHA-1(bridge;time=36124135;seq=311))@localhost
To: sip: participant1@localhost
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24)) @localhost
CSeq: 12002 BYE
The Bridge responds to MTA-t1 with the expected acknowledgement
message.
DCS Group Category: Informational - Expiration 8/31/02 112
DCS Architecture February 2002
(2) 200-OK
SIP/2.0 200 OK
Via: SIP/2..0/UDP Host(mta-t1.provider)
From: sip:B64(SHA-1(bridge;time=36124135;seq=311))@localhost
To: sip: participant1@localhost
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24)) @localhost
CSeq: 12002 BYE
The Bridge now reconnects the two remaining parties into a simple
call. Since MTA-o is the originator of the three-way-call, the
Bridge informs it of the need to redirect the call from MTA-t2.
Bridge sends the INVITE(Also,Replace) message, via Proxy-b.
(3) REFER
REFER sip:Host(mta-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mcu41.provider)
Supported: 100rel, state
Refer-To: tel:+1-212-555-3333 ? Call-ID= B64(SHA-1(555-
1111;time=36124135;seq=24))@localhost & Reffered-By=
sip:B64(SHA-1(bridge;time=36124135;seq=312))@localhost
& State= Host(dp-b.provider); state="{gate= Host(cmts-
b.provider): 3612/18S37624, nexthop=sip:+1-212-555-
3333;rn=+1-212-234-3333@Host(DP-t2), state="Host(dp-
t2.provider); nexthop=sip:555-3333@Host(mta-
t2.provider); gate=Host(cmts-
t2.provider):3621/13S52196; orig-dest=tel:+1-212-555-
3333; num-redirects=0"}K"
State: Host(dp-b.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-b.provider):3612/15S30179;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
1111; num-redirects=0"}K"
From: sip:bridge@Host(dp-o.provider)
To: B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
CSeq: 12301 INVITE
Refer-By: sip:bridge@Host(dp-o.provider)
The call flow from this point onward is identical to the Call
Transfer with Consultation, as shown in Section 10.12. The bridge,
having "consulted" with MTA-o, transfers its call with MTA-t2 to
MTA-o.
DCS Group Category: Informational - Expiration 8/31/02 113
DCS Architecture February 2002
MTA-o MTA-t1 MTA-t2 Proxy-b Bridge
| | | (1) BYE | |
|----------------------------------------------------->|
| | | (2) 200 OK | |
|<-----------------------------------------------------|
| | | | |
| | | (3) BYE | |
| | |<----------------------------------|
| | | (4) 200 OK | |
| | |---------------------------------->|
| | | | |
| | | (5) BYE | |
| |<--------------------------------------------|
| | | (6) 200 OK | |
| |-------------------------------------------->|
| | | | |
When the originator of a three-way call hangs up, the entire call is
terminated. The bridge recognizes the BYE from the originator and
sends BYE messages to all participants.
MTA-o -> Bridge
(1) BYE
BYE sip:Host(mcu41.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
From: sip:B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
To: sip:bridge@Host(dp-o.provider)
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
CSeq: 141 BYE
Bridge -> MTA-o
(2) 200-OK
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-o.provider)
From: sip:B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
To: sip:bridge@Host(dp-o.provider)
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
Cseq: 141 BYE
Bridge -> MTA-t2
DCS Group Category: Informational - Expiration 8/31/02 114
DCS Architecture February 2002
(3) BYE
BYE sip:Host(mta-t2.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mcu41.provider)
From: sip:B64(SHA-1(bridge;time=36124135;seq=312))@localhost
To: sip: participant2@localhost
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
CSeq: 80001 BYE
MTA-t2 -> Bridge
(4) 200-OK
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mcu41.provider)
From: sip:B64(SHA-1(bridge;time=36124135;seq=312))@localhost
To: sip: participant2@localhost
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
CSeq: 80001 BYE
Bridge -> MTA-t1
(5) BYE
BYE sip:Host(mta-t1.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mcu41.provider)
From: sip:B64(SHA-1(bridge;time=36124135;seq=311))@localhost
To: sip: participant1@localhost
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
CSeq: 80002 BYE
MTA-t1 -> Bridge
(6) 200-OK
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mcu41.provider)
From: sip:B64(SHA-1(bridge;time=36124135;seq=311))@localhost
To: sip: participant1@localhost
Call-ID: B64(SHA-1(555-1111;time=36124135;seq=24))@localhost
CSeq: 80002 BYE
DCS Group Category: Informational - Expiration 8/31/02 115
DCS Architecture February 2002
10.15 CODEC Change within previous authorization
When the initial INVITE SDP contained multiple CODECs, such that any
single CODEC would be authorized, no further interaction is needed
with the CMS/Proxies to change CODECs. However, due to the
requirements of the segmented reservation model of D-QoS, it is
necessary to signal to the far end and synchronize changes in CODEC
usage. The following diagram shows the sequence of signaling
messages to perform this function.
MTA-o Proxy-o Proxy-b MTA-t
| | (1) INVITE | |
|----------------------------------------------------->|
| | (2) 183 SDP | |
|<-----------------------------------------------------|
| | (3) PRACK | |
|----------------------------------------------------->|
| | (4) 200 OK | |
|<-----------------------------------------------------|
| | (5) COMET | |
|----------------------------------------------------->|
| | (6) 200 OK | |
|<-----------------------------------------------------|
| | | |
| | (7) 200 OK | |
|<-----------------------------------------------------|
| | (8) ACK | |
|----------------------------------------------------->|
| | | |
By some mechanism outside the scope of the Distributed Call
Signaling protocol, MTA-o decides that a CODEC change is necessary.
MTA-o sends the following INVITE message directly to MTA-t. This
INVITE is almost identical to the initial INVITE that established
the call, except for header fields such as Remote-Party-ID and
Anonymity that are not sent to maintain originator privacy.
(1) INVITE:
INVITE sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost >
DCS Group Category: Informational - Expiration 8/31/02 116
DCS Architecture February 2002
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
CSeq: 129 INVITE
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 3456 RTP/AVP 0
Upon receipt of the (1) INVITE message, MTA-t verifies its ability
to switch to the designated CODEC, and responds with a 183-Session-
Progress including an updated SDP. The procedures from this point
onward are identical to a basic call flow, as given in Section 10.1.
The resource reservations done in this call flow maintain the
previous resources, so that if either end fails to make the proper
reservation, the original call can proceed with the initial CODEC.
MTA-t actually switches to the new codec upon sending the final 200-
OK response to the INVITE, and MTA-o switches to the new codec upon
receipt of the final 200-OK.
DCS Group Category: Informational - Expiration 8/31/02 117
DCS Architecture February 2002
10.16 CODEC Change requiring new authorization
When an MTA wishes to change to a different CODEC, but that CODEC
was not among those initially authorized (or subsequently authorized
by this sequence), it is necessary to request an increased
authorization from the Proxy. The following diagram shows the
sequence of signaling messages that achieves this.
MTA-o Proxy-o Proxy-t2 MTA-t1 MTA-t2
| (1) INVITE | | | |
|----------------->| (2) INVITE | | |
| |-------------->| (3) INVITE |
| | |------------------>|
| | | (4) 183 SDP |
| | (5) 183 SDP |<------------------|
| (6) 183 SDP |<--------------| | |
|<-----------------| (7) PRACK | | |
|----------------------------------------------------->|
| | (8) 200 OK | |
|<-----------------------------------------------------|
| | (9) COMET | |
|----------------------------------------------------->|
| | (10) 200 OK | |
|<-----------------------------------------------------|
| | | (11) 200 OK |
| | (12) 200 OK |<------------------|
| (13) 200 OK |<--------------| |
|<-----------------| (14) ACK | |
|----------------------------------------------------->|
| | | |
By some mechanism outside the scope of the Distributed Call
Signaling protocol, MTA-o decides that a CODEC change is necessary,
and that the previous authorization for the current call does not
permit this new CODEC (e.g. the initial call setup used only G.726-
32 and the new CODEC desired is G.711). MTA-o generates the
following SIP INVITE message and sends it to Proxy-o (the Proxy that
manages MTA-o). MTA-o starts timer (T-proxy-request).
(1) INVITE:
INVITE sip:555-2222@Host(DP-o);user=phone SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
DCS Group Category: Informational - Expiration 8/31/02 118
DCS Architecture February 2002
Supported: 100rel, state
State: Host(dp-o.provider); state="{gate= Host(cmts-
o.provider): 3612/17S30124, nexthop=sip:+1-212-555-
2222;rn=+1-212-234-2222@Host(DP-t), state="Host(dp-
t.provider); nexthop=sip:555-2222@Host(mta-t.provider);
gate=Host(cmts-t.provider):4321/31S14621; orig-
dest=tel:+1-212-555-1111; num-redirects=0"}K"
Remote-Party-ID: John Doe <tel:555-1111>
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
CSeq: 129 INVITE
Content-Type: application/sdp
Content-length: (.)
v=0
O=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=X-pc-csuites:312F
a=rtpmap:0 PCMU/8000
m=audio 3456 RTP/AVP 0
a=qos: mandatory sendrecv
Upon receiving the INVITE message, Proxy-o authenticates MTA-o using
standard IPSec authentication. Proxy-o decodes the state string in
the State header and extracts the relevant information about the
current call. Proxy-o generates the following INVITE message and
sends it to Proxy-t. Proxy-o adds a number of parameters to the
INVITE message. These are shown below.
(2) INVITE:
INVITE sip: +1-212-555-2222;rn=+1-212-234-2222;
npdi=yes@Host(DP-t);user=phone SIP/2.0
Via: SIP/2.0/UDP Host(DP-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
Require: state
Proxy-Require: dcs, state
Dcs-Gate: Host(cmts-o.provider): 3612/17S30124
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/212-
555-1111/212-555-2222>
Dcs-Billing-ID: Host(dp-o.provider):36123E5C:0152
State: Host(dp-t.provider); nexthop=sip:555-2222@Host(mta-
t.provider); gate=Host(cmts-t.provider):4321/31S14621;
orig-dest=tel:+1-212-555-1111; num-redirects=0
Remote-Party-ID: John Doe <tel:+1-212-555-1111>
DCS Group Category: Informational - Expiration 8/31/02 119
DCS Architecture February 2002
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 INVITE
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 3456 RTP/AVP 0
a=qos: mandatory sendrecv
Upon receiving this INVITE message, Proxy-t recognizes this as a
mid-call change by the presence of the State header with its name
attached, and generates the following INVITE message and sends it to
MTA-t. Note that the Via lines may be different from the initial
INVITE exchange; they have been encrypted to maintain the privacy of
the caller.
(3) INVITE:
INVITE sip:555-2222@Host(mta-t.provider); user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider);branch=1"; via=Host(mta-o.provider)}K
Supported: 100rel, stateMedia-Authorization: 31S14621
Remote-Party-ID: John Doe <tel:+1-212-555-1111>
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 INVITE
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 3456 RTP/AVP 0
a=qos: mandatory sendrecv
DCS Group Category: Informational - Expiration 8/31/02 120
DCS Architecture February 2002
Upon receiving this INVITE, MTA-t authenticates that the message
came from Proxy-t using IPSec. MTA-t checks for a current call
matching the triple (From, To, Call-ID). MTA-t looks at the
capability parameters in the Session Description Protocol (SDP) part
of the message and determines which media channel parameters it can
accommodate for this call. MTA-t generates the following 183-
Session-Progress response, and sends it to Proxy-t.
(4) 183 Session-Progress:
SIP/2.0 183 Session Progress
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider);branch=1"; via=Host(mta-o.provider)}K
Require: 100rel
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
Remote-Party-ID: John Smith <tel: 555-2222>
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 INVITE
Content-Disposition: precondition
Contact: sip:Host(mta-t.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-t.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=rtpmap:0 PCMU/8000
m=audio 6544 RTP/AVP 0
a=qos: mandatory sendrecv confirm
Upon receiving the 200-OK message, Proxy-t authorizes the resources
and forwards the following 183-Session-Progress to Proxy-o,
restoring the Via headers. At this point Proxy-t has completed its
transaction and does not maintain any more state for this call.
Proxy-t may include Dcs-Billing-Information if it wishes to override
the billing information that came in the INVITE (e.g. collect or
toll-free call).
(5) 183-Session-Progress:
SIP/2.0 183 Session Progress
Via: SIP/2.0/UDP Host(dp-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
DCS Group Category: Informational - Expiration 8/31/02 121
DCS Architecture February 2002
Require: 100rel
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124;
orig-dest=tel:+1-212-555-2222; num-redirects=0
Remote-Party-ID: John Smith <tel: +1-212-555-2222>
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 INVITE
Content-Disposition: precondition
Contact: sip:Host(mta-t.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-t.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=rtpmap:0 PCMU/8000
m=audio 6544 RTP/AVP 0
a=qos: mandatory sendrecv confirm
Upon receiving the 183-Session-Progress message, Proxy-o authorizes
the resources and forwards the following message to MTA-o. At this
point Proxy-o has completed its transaction and does not maintain
any more state for this call.
(6) 183-Session-Progress:
SIP/2.0 183 Session Progress
Via: Sip/2.0/UDP Host(mta-o.provider)
Require: 100rel
Remote-Party-ID: John Smith <tel: +1-212-555-2222>
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 INVITE
Content-Disposition: precondition
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-t.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
DCS Group Category: Informational - Expiration 8/31/02 122
DCS Architecture February 2002
a=rtpmap:0 PCMU/8000
m=audio 6544 RTP/AVP 0
a=qos: mandatory sendrecv confirm
Upon receiving the 183-Session-Progress message, MTA-o sends the
PRACK message directly to MTA-t using the IP address in the Contact
header. MTA-o then reserves the resources needed, and sends a COMET
message if successful. The COMET message, and the 200-OK messages
in response to the PRACK and COMET are identical to that in the
basic call flow (Section 10.1) and not shown here.
(7) PRACK:
PRACK sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
CSeq: 130 PRACK
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 3456 RTP/AVP 0
a=qos: mandatory sendrecv
MTA-t reserves the resources as needed from the final SDP from the
PRACK message. If successful, and upon receipt of the COMET message
from MTA-o indicating it was successful, MTA-t changes the CODEC and
sends the 200-OK final response.
(11) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider);branch=1"; via=Host(mta-o.provider)}K
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
CSeq: 129 INVITE
DCS Group Category: Informational - Expiration 8/31/02 123
DCS Architecture February 2002
Upon receiving the 200-OK message, Proxy-t forwards the following
200-OK to Proxy-o, restoring the Via headers.
(12) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(dp-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124;
orig-dest=tel:+1-212-555-2222; num-redirects=0
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
CSeq: 129 INVITE
Upon receiving the 200-OK message, Proxy-o forwards the following
200-OK to MTA-o.
(13) 200-OK:
SIP/2.0 200 OK
Via: Sip/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
CSeq: 129 INVITE
Upon receiving the 200-OK message, MTA-o sends the following ACK
message directly to MTA-t using the IP address in the Contact header
of the previous 183 message. This completes the three-way handshake
for the SIP INVITE exchange.
(14) ACK:
ACK sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
CSeq: 129 ACK
DCS Group Category: Informational - Expiration 8/31/02 124
DCS Architecture February 2002
10.17 Busy-Line-Verification
PSTN G/W CMS/MGC Proxy-t2 MTA-t2
| (1) NTFY | | |
|----------------->| | |
| (2) CRCX | | |
|<-----------------| | |
| (3) ACK | | |
|----------------->| | |
| | | |
| | (4) INVITE | |
| |-------------->| (5) INVITE |
| | |------------------>|
| | | (6) 183 SDP |
| | (7) 183 SDP |<------------------|
| |<--------------| |
| | (8) PRACK | |
| |---------------------------------->|
| | (9) 200 OK | |
| |<----------------------------------|
| | (10) COMET | |
| |---------------------------------->|
| | (11) 200 OK | |
| |<----------------------------------|
| | | (14) 200 OK |
| | (15) 200 OK |<------------------|
| |<--------------| |
| | (16) ACK | |
| |---------------------------------->|
| | | |
This service clearly requires the cooperation of the MTA. Further,
there is a network database of phone numbers of customers who cannot
be verified and/or broken into. It seems reasonable that a MTA that
refuses to cooperate is merely one so marked in the current
database.
Busy Line Verification sequence begins when the Operator at an OSPS
console signals an E.164 number for verification over a special MF
trunk group, to the PSTN gateway. The Media Gateway (MG) and Media
Gateway Controller (MGC) recognize this special signaling, and
generate an INVITE(BLV) to the number requested.
The normal call initiation sequence in TGCP is followed. The NTFY
message (1) signals the MGC of a call request, and MGC uses the CRCX
DCS Group Category: Informational - Expiration 8/31/02 125
DCS Architecture February 2002
message (2) and ACK (3) to generate an appropriate SDP. That it is
a OSPS trunk group is known to the MGC, which invokes the special
header insertion.
MGC recognizes the trunk group as special BLV trunks, and generates
a slightly modified INVITE message, by adding the Dcs-OSPS header.
(4) INVITE (BLV):
INVITE sip:212-555-1111,lnp=212-237@dp-t.provider;user=phone
SIP/2.0
Via: SIP/2.0/UDP Host(mgc02.provider);branch=1
Supported: 100rel, state
Proxy-Require: dcs
Remote-Party-ID: Operator <sip:Operator42@mgc02.provider>;
rpi-type=operator
Anonymity: URL
Dcs-OSPS: BLV
Dcs-Gate: mgc02.provider/36123E5B
Dcs-Billing-Info: Host(rks-o.provider)<OSPS/212-0/212-555-1111>
Dcs-Billing-ID: Host(mgc02.provider):36123E5C:0152
From: B64(SHA-1(0;time=36123E5B;seq=72))@localhost
To: tel:555-1111
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
CSeq: 127 INVITE
Contact: sip:mgc02.provider
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 mg101.provider
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3380 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Proxy-t authorizes the additional connection without regard to
number of currently active connections, and passes the INVITE(BLV)
to MTA-t.
(5) INVITE (BLV):
INVITE sip:212-555-1111@mta-t.provider;user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-t.provider);branch=1, {
via="Host(mgc02.provider);branch=1"}K
Supported: 100rel, state
Require: state
DCS Group Category: Informational - Expiration 8/31/02 126
DCS Architecture February 2002
Remote-Party-ID: Operator <sip:{type=remote-id;
orig=sip:Operator42@mgc02.provider; anonymity=URL}K>;
rpi-type=operator
Dcs-OSPS: BLV
Dcs-Gate: 44S10312
State: Host(dp-t.provider); state="{nexthop=sip:Host(mgc02.
Provider); gate=Host(cmts-t.provider):4321/44S10312}K"
From: B64(SHA-1(0;time=36123E5B;seq=72))@localhost
To: tel:555-1111
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:mgc02.provider
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 mg101.provider
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3380 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
MTA-t does not respond to a BLV request with BUSY, nor does it
perform call forwarding. The response is 183-Session-Progress,
identical to that of a normal call given in Section 10.1, and
completes identical to a normal call (but without the ringing
phase).
MTA-t commits to the reserved resources, and begins to send voice
packets to the Operator. The payload contains a copy of the packets
generated at MTA-t.
If the designated line is onhook, MTA-t will generate silence
packets and send to Operator. If the line is currently ringing or
generating local ringback, MTA-t will generate a ringback tone
pattern and sent to Operator.
The OSPS system scrambles the received voice packets, making the
conversation unintelligible to the Operator. However, enough
information is passed through the scrambled audio for the operator
to accurately determine whether the line is in use, dialing,
ringing, or idle.
A BLV call terminates when the OSPS signals a hangup over the MF
trunk, resulting in a DCS BYE message. The MTA never terminates a
BLV call.
DCS Group Category: Informational - Expiration 8/31/02 127
DCS Architecture February 2002
10.18 Operator break-in
PSTN G/W CMS/MGC Proxy-t2 MTA-t2
| (1) NTFY | | |
|----------------->| | |
| (2) CRCX | | |
|<-----------------| | |
| (3) ACK | | |
|----------------->| | |
| | | |
| | (4) INVITE | |
| |-------------->| (5) INVITE |
| | |------------------>|
| | | (6) 183 SDP |
| | (7) 183 SDP |<------------------|
| |<--------------| |
| | (8) PRACK | |
| |---------------------------------->|
| | (9) 200 OK | |
| |<----------------------------------|
| | (10) COMET | |
| |---------------------------------->|
| | (11) 200 OK | |
| |<----------------------------------|
| | | (14) 200 OK |
| | (15) 200 OK |<------------------|
| |<--------------| |
| | (16) ACK | |
| |---------------------------------->|
| (17) NTFY | | |
|----------------->| | |
| | (18) INVITE | |
| |---------------------------------->|
| | (19) 200 OK | |
| |<----------------------------------|
| | (20) ACK | |
| |---------------------------------->|
| | | |
Emergency Interrupt is closely tied to BLV (previous appendix),
since EI always begins with BLV. Messages (1) through (16) perform
the BLV function, and are not repeated here.
DCS Group Category: Informational - Expiration 8/31/02 128
DCS Architecture February 2002
At the end of the BLV call flow, instead of the OSPS releasing the
trunk, OSPS generates an alerting tone. The Media Gateway (MG)
detects activity on line and the Media Gateway Controller (MGC)
generates INVITE(EI) and sends it direct to MTA-t.
(18) INVITE(EI):
INVITE sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mgc02.provider)
From: B64(SHA-1(0;time=36123E5B;seq=72))@localhost
To: tel:555-1111
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
CSeq: 130 INVITE
Dcs-OSPS: EI
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 mgc02.provider
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 3380 RTP/AVP 0
MTA verifies that BLV is already active, and that the EI request
matches From, To, Call-ID. If so, it responds with 200-OK. SDP is
not needed unless there is a change in the session description from
that of the BLV.
(19) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mgc02.provider)
From: B64(SHA-1(0;time=36123E5B;seq=72))@localhost
To: tel:555-1111
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
CSeq: 130 INVITE
MGC responds with the standard SIP ACK message.
MTA has several choices of how to do the EI function. 1) put
current call on hold and connect user to operator. 2) perform local
mixing of current call and stream from OSPS, so both participants in
existing call hear and can talk to the operator. 3) allocate a
bridge and treat this just like a 3-way call.
DCS Group Category: Informational - Expiration 8/31/02 129
DCS Architecture February 2002
10.19 Lawfully Authorized Electronic Surveillance
Calls from and to surveillance subjects behave just like a normal
call flows. Additional messages will be sent from the CMS to the
Electronic Surveillance Delivery Function telling the known
signaling information. One additional parameter is sent to the CMTS
in the Gate-Set command, telling it to copy all the voice data
packets and send the copy to the Law Enforcement Access Point.
There is no change to the MTA-CMS message exchanges due to
electronic surveillance. This is an absolute requirement due to the
non-intrusive requirement of the electronic surveillance statute.
In most cases, there is no change to the CMS-CMS message exchanges
due to electronic surveillance. This basic design keeps the
knowledge of surveillance as localized as possible. If a call
originator is under surveillance, the surveillance is done at the
originating CMTS; the call destination does not know in any way that
it is happening. If a call destination is under surveillance, the
surveillance is done at the terminating CMTS; the call originator
does not know in any way that it is happening. If both the call
originator and call destination are under surveillance, the
interception is done twice. So it goes.
The only situation where CMS-CMS message exchanges are extended to
support electronic surveillance is in cases of call redirection.
When a subject under surveillance initiates a call transfer, it is
required that the new call also be intercepted. Therefore the
notification of surveillance is passed in that CMS-CMS INVITE
message. Further, when the new destination is unable to perform the
required interception (e.g. redirection to a network server such as
voicemail), the 183 response contains additional information telling
the originator to perform the surveillance. These situations are
shown in the following examples.
DCS Group Category: Informational - Expiration 8/31/02 130
DCS Architecture February 2002
10.19.1 Call-Forwarding-Unconditional with Forwarder under Surveillance
MTA-o Proxy-o Proxy-t MTA-t
| INVITE | | |
|----------------->| INVITE | |
| |-------------->| (1)INVITE |
| | |------------------>|
| | | (2)302 Redirect |
| | |<------------------|
| | (3)302 | |
| |<--------------| (4)ACK |
| | |------------------>|
| | (5)ACK | |
| |-------------->| |
| |
| | Proxy-f MTA-f
| | | |
| | (6)INVITE | |
| |-------------->| (7)INVITE |
| | |------------------>|
| | | (8)183 SDP |
| | |<------------------|
| | | |
For this example, consider a call from MTA-o to MTA-t (with MTA-t
under surveillance). MTA-t has established call forwarding-
unconditional. The basic call flow for call-forwarding is identical
to that given in Section 10.5, and only the differences are noted
here.
(1) INVITE:
INVITE sip:555-2222@Host(mta-t.provider); user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
Supported: 100rel, state
Require: state
Remote-Party-ID: John Doe <tel:+1-212-555-1111>
Media-Authorization: 31S14621
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
DCS Group Category: Informational - Expiration 8/31/02 131
DCS Architecture February 2002
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Upon receiving this message, MTA-t determines that the line
associated with 212-555-2222 is having all calls forwarded. It
issues a REDIRECT (302) response to indicate that it wants the call
forwarded. This message carries the forwarding number in the Contact
header.
(2) 302-Redirect
SIP/2.0 302 Moved Temporarily
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
Remote-Party-ID: John Smith <tel:555-2222>
Anonymity: off
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: tel:555-3333
Proxy-t knows that MTA-t is under surveillance, and includes the
Dcs-Laes header in the 302-Redirect response sent back to CMS-o.
DCS Group Category: Informational - Expiration 8/31/02 132
DCS Architecture February 2002
This header contains the delivery function information needed by the
new destination of the call.
(3) 302-Redirect
SIP/2.0 302 Moved Temporarily
Via: SIP/2.0/UDP Host(dp-o.provider); branch = 1
Via: SIP/2.0/UDP Host(mta-o.provider)
Proxy-Require: dcs
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/212-
555-1111/212-555-2222>
Dcs-Billing-Info: Host(rks-t.provider)<4278-9865-8765-9000/212-
555-2222/212-555-3333>
Dcs-Billing-ID: Host(dp-o.provider):36123E5C:0152
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124;
orig-dest=tel:+1-212-555-2222; num-redirects=0
Remote-Party-ID: John Smith <tel:+1-212-555-2222>
Anonymity: off
Dcs-Laes: Host(df-t)/Host(df-t);surveillancekey
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: tel:+1-212-555-3333
Proxy-o determines the Proxy-f for the E.164 number 212-555-3333
when it receives the 302-Redirect message. It generates an INVITE
message and sends it to Proxy-f. Proxy-o adds the Dcs-Laes header to
this INVITE, with the delivery function information received from
Proxy-t. Proxy-o adds the Dcs-Redirect header giving the
information about this call redirection.
(6) INVITE:
INVITE sip:+1-212-555-3333;rn=+1-212-265-3333;
npdi=yes@Host(dp-f) ;user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-o.provider); branch = 2
Via: SIP/2.0/UDP Host(mta-o.provider);
Supported: 100rel, state
Require: state
Proxy-Require: dcs, state
Remote-Party-ID: John Doe; <tel:+1-212-555-1111>
Anonymity: Off
Dcs-Gate: Host(cmts-o.provider):3612/17S30124/37FA1948 required
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/212-
555-1111/212-555-2222>
Dcs-Billing-Info: Host(rks-t.provider)<4278-9865-8765-9000/212-
555-2222/212-555-3333>
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124;
orig-dest=tel:+1-212-555-2222; num-redirects=1
Dcs-Laes: Host(df-t)/Host(df-t);surveillancekey
Dcs-Redirect: <tel:+1-212-555-2222> <tel:+1-212-555-2222> 1
DCS Group Category: Informational - Expiration 8/31/02 133
DCS Architecture February 2002
Dcs-Billing-ID: Host(dp-o.provider):36123E5C:0152
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
CSeq: 127 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Upon receiving this INVITE, Proxy-f queries the directory server to
determine the IP address (MTA-f) associated with 212-555-3333. It
then forwards the INVITE message to MTA-f. Included in the State
header is the additional surveillance information.
(7) INVITE:
INVITE sip:555-3333@Host(mta-f.provider); user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-f.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
Supported: 100rel, state
Require: state
Remote-Party-ID: John Doe <tel:+1-212-555-1111>
Media-Authorization: 22S21718
State: Host(dp-f.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-f.provider):4321/22S21718;
laes=full; redirect=<tel:+1-212-555-2222> <tel:+1-212-
555-2222> 1; state="Host(dp-o.provider);
nexthop=sip:555-1111@Host(mta-o.provider);
gate=Host(cmts-o.provider):3612/17S30124; orig-
dest=tel:+1-212-555-2222; num-redirects=1"}K"
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
DCS Group Category: Informational - Expiration 8/31/02 134
DCS Architecture February 2002
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
The subsequent signaling call flows are identical to those shown in
Section 10.5.
10.19.2 Call-Transfer-Blind with Transferer under Surveillance
MTA-o Proxy-o Proxy-t MTA-t
| | | |
|<-----------------call-in-progress------------------->|
| | | (1) REFER |
| | (2) REFER |<------------------|
| (3) REFER |<--------------| |
|<-----------------| | |
| |
| | Proxy-f MTA-f
| (4) INVITE | | |
|----------------->| (5) INVITE | |
| |-------------->| (6) INVITE |
| | |------------------>|
| | | (7) 183 SDP |
| | (8) 183 SDP |<------------------|
| (9) 183 SDP |<--------------| :
|<-----------------| : :
: : : (10) 200 OK |
: : (11) 200 OK |<------------------|
| (12) 200 OK |<--------------| |
|<-----------------| | |
| |
| | Proxy-t MTA-t
| (13) 200 OK | | |
|----------------->| (14) 200 OK | |
| |-------------->| (15) 200 OK |
| | (16) ACK |------------------>|
|<-----------------------------------------------------|
| | (17) BYE | |
|----------------------------------------------------->|
| | (18) 200 OK | |
DCS Group Category: Informational - Expiration 8/31/02 135
DCS Architecture February 2002
|<-----------------------------------------------------|
| |
For this example, consider an existing call initiated by MTA-o to
MTA-t (with MTA-t under surveillance), with the following call
identification. The only difference from a normal call from MTA-o
to MTA-t, as given elsewhere in this specification, is the addition
of "laess=full" in the encrypted call state information associated
with Proxy-t.
MTA-t state for call from MTA-o to MTA-t
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Contact: sip:Host(mta-o.provider)
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
laes=full; state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
Dcs-Billing-Info: Host(rks-o.provider)/04FA37<5123-0123-4567-
8900/212-555-1111/212-555-2222>
Dcs-Billing-ID: Host(dp-o.provider):36123E5C:0152
The basic call flow for call transfer is identical to that given in
Section 10.11, and only the differences are noted here.
MTA-t desires to transfer the existing call to 555-3333 and issues a
REFER message, identical to (1) in Section 10.11.
Proxy-t decrypts the State information and sees the "laes=full." It
inserts one additional header component into the Refer-to header,
giving the local Electronic Surveillance Delivery Function's (DF's)
address information and security key to use for messages to the DF.
Since surveillance was marked as "full," it adds the DF's address
for both signaling information and for call content.
(2) REFER:
REFER sip: Host(dp-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(dp-t.provider)
Via: SIP/2.0/UDP Host(mta-t.provider)
Supported: 100rel, state
Proxy-Require: dcs
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124;
orig-dest=tel:+1-212-555-2222; num-redirects=0
Refer-to: tel:+1-212-555-3333? Dcs-Billing-Info= Host(rks-
o.provider)<5123-0123-4567-8900/212-555-1111/212-555-
2222> & Dcs-Billing-Info= Host(rks-t.provider)<4278-
9865-8765-9000/212-555-2222/212-555-3333> & Dcs-
Billing-ID= Host(dp-o.provider): 36123E5C:0152 & Dcs-
Laes= Host(df-t)/Host(df-t);surveillancekey & Dcs-
Redirect=<tel:+1-212-555-2222><tel:+1-212-555-2222>1
DCS Group Category: Informational - Expiration 8/31/02 136
DCS Architecture February 2002
Remote-Party-ID: John Smith <tel:+1-212-555-2222>
From: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
To: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 8001 REFER
Referred-by: sip:B64(SHA-1(555-2222; time=36123E5B;
seq=73))@localhost
Proxy-o includes the Dcs-Laes information in the encrypted URL given
to MTA-t.
(3) REFER:
REFER sip: Host(mta-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(dp-o.provider), {via="Host(dp-
t.provider); branch=1"; via=Host(mta-t.provider)}K
Supported: 100rel, stateRefer-to: sip:{type=transfer;
dest=tel:+1-212-555-3333; billing-id=Host(dp-o.provider):
36123E5C:0152; expires=<timestamp>; billing-info=Host(rks-
o.provider)<5123-0123-4567-8900/212-555-1111/212-555-
2222>; billing-info=Host(rks-t.provider)<4278-9865-
8765-9000/212-555-2222/212-555-3333>; laes="Host(df-
t)/Host(df-t);surveillancekey"; redirect=<tel:+1-212-
555-2222><tel:+1-212-555-2222>1}K@Host(dp-
o.provider); user=private
From: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
To: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 8001 REFER
Referred-by: sip:B64(SHA-1(555-2222; time=36123E5B;
seq=73))@localhost
After processing the REFER, MTA-o issues a INVITE to MTA-f. In
addition to the standard headers carried in an INVITE message, the
encrypted Dcs-Laes fields received in the REFER message are copied
into the INVITE message.
(4) INVITE:
INVITE sip:{type=transfer; dest=tel:+1-212-555-3333; billing-
id=Host(dp-o.provider): 36123E5C:0152;
expires=<timestamp>; billing-info=Host(rks-
o.provider)<5123-0123-4567-8900/212-555-1111/212-555-
2222>; billing-info=Host(rks-t.provider)<4278-9865-
8765-9000/212-555-2222/212-555-3333>; laes="Host(df-
t)/Host(df-t);surveillancekey"; redirect=<tel:+1-212-
555-2222><tel:+1-212-555-2222>1}K@Host(dp-
o.provider); user=private SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
Remote-Party-ID: John Doe <tel:555-1111>
Anonymity: Off
DCS Group Category: Informational - Expiration 8/31/02 137
DCS Architecture February 2002
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E98;
seq=74))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E98; seq=75))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E98;seq=74))@localhost
Cseq: 129 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
When the Proxy-o receives the INVITE it decrypts the header
information to find the real destination, and discovers the Dcs-Laes
information. This is included in the INVITE message sent to Proxy-
f. Proxy-o also includes a Dcs-Redirect header giving the original
destination for the call from MTA-o, the forwarding endpoint, and
the number of redirections that have occurred to this call.
(5) INVITE:
INVITE sip: +1-212-555-3333;rn=+1-212-265-3333;
npdi=yes@Host(dp-f);user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-o.provider); branch=1;
Via: SIP/2.0/UDP Host(mta-o.provider);
Supported: 100rel, state
Require: state
Proxy-Require: dcs, state
Remote-Party-ID: John Doe <tel:+1-212-555-1111>
Anonymity: Off
Dcs-Gate: Host(cmts-o.provider):3612/17S30124/37FA1948
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/212-
555-1111/212-555-2222>
Dcs-Billing-Info: Host(rks-t.provider)<4278-9865-8765-9000/212-
555-2222/212-555-3333>
Dcs-Billing-ID: Host(dp-o.provider):36123E5C:0152
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124;
orig-dest=tel:+1-212-555-2222; num-redirects=1
Dcs-Laes: Host(df-t)/Host(df-t);surveillancekey
Dcs-Redirect: <tel:+1-212-555-2222> <tel:+1-212-555-2222> 1
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E98;
seq=74))@localhost>
DCS Group Category: Informational - Expiration 8/31/02 138
DCS Architecture February 2002
To: sip:B64(SHA-1(555-2222; time=36123E98; seq=75))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E98;seq=74))@localhost
Cseq: 129 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Upon receiving this INVITE, Proxy-f includes the surveillance
information in its Gate-Set command, and passes the call-identifying
information to its local Electronic Surveillance Delivery Function
(DF-f) who passes the information on to DF-t. The encrypted State
value stored at MTA-f includes the surveillance parameters needed
for possible mid-call transfers.
(6) INVITE:
INVITE sip:555-3333@Host(mta-f.provider); user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-f.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
Supported: 100rel, state
Require: state
Remote-Party-ID: John Doe; <tel:+1-212-555-1111>
Media-Authorization: 31S14621
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
laes=full; redirect=<tel:+1-212-555-2222><tel:+1-212-
555-2222>1; state="Host(dp-o.provider);
nexthop=sip:555-1111@Host(mta-o.provider);
gate=Host(cmts-o.provider):3612/17S30124; orig-
dest=tel:+1-212-555-2222; num-redirects=0"}K"
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E98;
seq=74))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E98; seq=75))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E98;seq=74))@localhost
Cseq: 129 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
DCS Group Category: Informational - Expiration 8/31/02 139
DCS Architecture February 2002
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
When the new call completes, MTA-o acknowledges receipt of the REFER
by sending a 200-OK to MTA-t. This is identical to Section 10.11.
Remainder of the call is identical to the basic call flow shown in
Section 10.11, and is not repeated here.
10.19.3 Call-Transfer with new destination unable to do interception
If CMS-f determines that it is unable to perform the required
surveillance, it passes the request back to CMS-o. This occurs, for
instance, if the new destination of this redirected call is a
voicemail server, or a announcement server, or a bridge server, or
any other network server that does not implement the capability to
intercept the media packets. CMS-f includes the Dcs-Laes header in
the 183-Session-Progress message as follows:
(8) 183-Session-Progress:
SIP/2.0 183 Session Progress
Via: SIP/2.0/UDP Host(dp-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
Require: 100rel
Proxy-Require: dcs
State: Host(dp-f.provider); nexthop=sip:555-3333Host(mta-
f.provider); gate=Host(cmts-f.provider):4321/31S14621;
orig-dest=tel:+1-212-555-1111; num-redirects=0
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124;
orig-dest=tel:+1-212-555-2222; num-redirects=1
Dcs-Gate: Host(cmts-t.provider):4321/31S14621/37FA1948
Remote-Party-ID: John Smith <tel:+1-212-555-2222>
Anonymity: off
Dcs-Laes: Host(df-o)/Host(df-o);surveillancekey
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
DCS Group Category: Informational - Expiration 8/31/02 140
DCS Architecture February 2002
Rseq: 9021
Content-Disposition: precondition
Contact: sip:Host(mta-t.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-t.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=rtpmap:0 PCMU/8000
m=audio 6544 RTP/AVP 0
a=qos:mandatory sendrecv confirm
Proxy-o performs the surveillance in its Gate-Set command to its
CMTS. Remainder of the call flow is identical to a normal call.
10.19.4 Call-Transfer-Consultative with Transferer under Surveillance
MTA-o MTA-t1 Proxy-o Proxy-t2 MTA-t2
| (1) REFER | | |
|----------------->| (2) REFER | |
| | |-------------->| (3) REFER |
| | | |------------------>|
| | | |
| | Proxy-t1 | (4) INVITE |
| | | (5)INVITE |<------------------|
| |(6)INVITE|<--------------| |
| |<--------| | |
| | (7)SDP | | |
| |-------->| (8) SDP | |
| | |-------------->| (9) SDP |
| | | (10) PRACK |------------------>|
| |<--------------------------------------------|
| | | (11) 200 OK | |
| |-------------------------------------------->|
| | | (12) COMET | |
| |<--------------------------------------------|
| | | (13) 200 OK | |
| |-------------------------------------------->|
| |(14)200 | | |
| |-------->| (15) 200 OK | |
| | |-------------->| (16) 200 OK |
| | | (17) ACK |------------------>|
| |<--------------------------------------------|
| | | | |
| | Proxy-o | (17) 200 OK |
| | | (18)200 OK |<------------------|
DCS Group Category: Informational - Expiration 8/31/02 141
DCS Architecture February 2002
| (19) 200 OK |<--------------| |
|<-----------------| | |
| | | (20) BYE | |
|----------------------------------------------------->|
| | | (21) 200 OK | |
|<-----------------------------------------------------|
|(22)BYE | | | |
|------->| | | |
|(23)200 | | | |
|<-------| | | |
After some period of consultation, MTA-o initiates a transfer of the
call from MTA-t1 to the new destination, MTA-t2. This involves
placing the second call on hold (message sequence described
earlier), and sending an INVITE(also,replace) message to MTA-t2,
giving it the information about the call with MTA-t1 in the Also:
header. The INVITE message, since it changes parties involved in
the call, is routed through the proxies. The sequence is shown in
the figure above, and detailed below.
For this example, consider a call initiated by MTA-t1 to MTA-x, with
MTA-x under surveillance, where MTA-x performed a blind transfer to
MTA-o. The call between MTA-t1 and MTA-o is therefore under
surveillance. MTA-o desires to transfer the call (with
consultation) to MTA-t2. After placing the call to MTA-t2, and
placing that call on hold, MTA-o initiates a transfer by sending a
REFER to MTA-t2, routed through the proxies.
The basic call flow for consultative transfer is identical to that
given in Section 10.12, and only the differences due to surveillance
are noted here.
(1) REFER:
REFER sip: Host(mta-t2.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
Remote-Party-ID: John Doe <tel:555-1111>
Anonymity: off
Refer-to: tel:+1-212-555-2222 ? Call-ID=B64(SHA-1(555-
1111;time=36124033;seq=72) & Referred-by=tel:555-1111
& State= Host(dp-o.provider);
state="{nexthop=sip:Host(dp-t1.provider);
gate=Host(cmts-o.provider):3612/17S30124; laes=full;
redirect=<tel:+1-212-555-7777><tel:+1-212-555-1111>2;
state="Host(dp-t1.provider); nexthop=sip:555-
2222@Host(mta-t1.provider); gate=Host(cmts-
t1.provider):4321/31S14621; orig-dest=tel:+1-212-555-
1111; num-redirects=0"}K"
State: Host(dp-o.provider); state="{gate= Host(cmts-
o.provider): 3612/3S10782, nexthop=sip:+1-212-555-
3333;rn=+1-212-256-3333@Host(dp-t2.provider),
state="Host(dp- t2.provider); nexthop=sip:555-
DCS Group Category: Informational - Expiration 8/31/02 142
DCS Architecture February 2002
3333@Host(mta- t2.provider); gate=Host(cmts-
t2.provider):4321/31S14621; orig-dest=tel:+1-212-555-
1111; num-redirects=0"}K"
From: sip:B64(SHA-1(555-1111;time=36124125;seq=23))@localhost
To: tel:555-3333
Call-ID: B64(SHA-1(555-1111;time=36124125;seq=23))@localhost
CSeq: 133 REFER
Referred-by: sip:B64(SHA-1(555-1111;time=36124125;
seq=23))@localhost
Proxy-o decrypts the State information in the Refer-To header to
determine the local state information. Proxy-o inserts billing
information and Electronis Surveillance information into the Refer-
To header. Proxy-o then forwards the message to Proxy-t1.
(2) REFER:
REFER sip: Host(dp-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(dp-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
Proxy-Require: dcs
State: Host(dp-t2.provider); nexthop=sip:555-3333@Host(mta-
t2.provider); gate=Host(cmts-
t2.provider):4321/31S14621; orig-dest=tel:+1-212-555-
1111; num-redirects=0
Refer-to: tel:+1-212-555-2222? Call-ID=B64(SHA-1(555-
1111;time=36124033;seq=72) & Referred-by=tel:555-1111
& Dcs-Billing-Info= Host(rks-t1.provider)<4278-9865-
8765-9000/212-555-2222/212-555-1111> & Dcs-Billing-
Info= Host(rks-t2.provider)<5123-0123-4567-8900/212-
555-1111/212-555-3333> & Dcs-Billing-ID= Host(dp-
o.provider): 36123E5C:0152 & Dcs-Laes=Host(df-
o)/Host(df-o);securitykey & Dcs-Redirect=<tel:+1-212-
555-7777><tel:+1-212-555-1111>2
Remote-Party-ID: John Smith <tel:+1-212-555-2222>
From: sip:B64(SHA-1(555-1111;time=36124125;seq=23))@localhost
To: tel:555-3333
Call-ID: B64(SHA-1(555-1111;time=36124125;seq=23))@localhost
CSeq: 133 REFER
Referred-by: sip:B64(SHA-1(555-1111;time=36124125;
seq=23))@localhost
Proxy-t2 forwards the REFER message to MTA-t2 after encrypting the
destination of the transfer, and the Electronic Surveillance
headers.
(3) REFER:
REFER sip: 555-3333@Host(mta-t2.provider) SIP/2.0
Via: SIP/2.0/UDP Host(dp-t2.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
Supported: 100rel, state
Refer-to: sip:{type=transfer; dest=tel:+1-212-555-2222;
billing-id=Host(dp-o.provider): 36123E5C:0152;
DCS Group Category: Informational - Expiration 8/31/02 143
DCS Architecture February 2002
expires=<timestamp>; billing-info= Host(rks-
t1.provider)<4278-9865-8765-9000/212-555-2222/212-555-
1111> ; billing-info= Host(rks-t2.provider)<5123-0123-
4567-8900/212-555-1111/212-555-3333>; laes=Host(df-
o)/Host(df-o);securitykey & redirect=<tel:+1-212-555-
7777><tel:+1-212-555-1111>2}K@Host(dp-t2.provider);
user=private ? Call-ID=B64(SHA-1(555-
1111;time=36124033;seq=72) & Referred-by=tel:555-1111
Remote-Party-ID: John Smith <tel:+1-212-555-2222>
From: sip:B64(SHA-1(555-1111;time=36124125;seq=23))@localhost
To: tel:555-3333
Call-ID: B64(SHA-1(555-1111;time=36124125;seq=23))@localhost
CSeq: 133 INVITE
Referred-by: sip:B64(SHA-1(555-1111;time=36124125;
seq=23))@localhost
After processing the REFER, MTA-t2 issues a INVITE to MTA-t1. In
addition to the standard headers carried in an INVITE message, the
encrypted {Dcs-Laes, Dcs-Redirect} fields received in the REFER
message are copied into the Request-URI of the INVITE message. These
fields indicate the surveillance information.
(4) INVITE:
INVITE sip:{type=transfer; dest=tel:+1-212-555-2222; billing-
id=Host(dp-o.provider): 36123E5C:0152;
expires=<timestamp>; billing-info= Host(rks-
t1.provider)<4278-9865-8765-9000/212-555-2222/212-555-
1111> ; billing-info= Host(rks-t2.provider)<5123-0123-
4567-8900/212-555-1111/212-555-3333>; laes=Host(df-
o)/Host(df-o);securitykey & redirect=<tel:+1-212-555-
7777><tel:+1-212-555-1111>2}K@Host(dp-t2.provider);
user=private SIP/2.0
Via: SIP/2.0/UDP Host(mta-t2.provider)
Supported: 100rel, state
Remote-Party-ID: John Smith <tel:555-3333>
Anonymity: Off
From: "Alien Blaster" <sip:B64(SHA-1(555-3333; time=36124172;
seq=74))@localhost>
To: sip:B64(SHA-1(555-3333; time=36124172; seq=75))@localhost
Call-ID: B64(SHA-1(555-1111;time=36124033;seq=72)@localhost
Cseq: 129 INVITE
Referred-by: tel:555-1111
Contact: sip:Host(mta-t2.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-t2.provider)
b=AS:64
t=907165275 0
DCS Group Category: Informational - Expiration 8/31/02 144
DCS Architecture February 2002
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
When the Proxy-t2 receives the INVITE it first decrypts the header
information to find the real destination for the call, and the
surveillance information.
(5) INVITE:
INVITE sip: +1-212-555-2222;rn=+1-212-265-2222;
npdi=yes@Host(dp-t1);user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-t2.provider); branch=1;
Via: SIP/2.0/UDP Host(mta-t2.provider);
Supported: 100rel, state
Require: state
Proxy-Require: dcs, state
Remote-Party-ID: John Smith <tel:+1-212-555-3333>
Anonymity: Off
Dcs-Gate: Host(cmts-t2.provider):3612/17S30124/37FA1948
Dcs-Billing-Info: Host(rks-t1.provider)<4278-9865-8765-
9000/212-555-2222/212-555-1111>
Dcs-Billing-Info: Host(rks-t2.provider)<5123-0123-4567-
8900/212-555-1111/212-555-3333>
Dcs-Billing-ID: Host(dp-o.provider):36123E5C:0152
Dcs-Laes: Host(df-o)/Host(df-o);securitykey
Dcs-Redirect: <tel:+1-212-555-7777><tel:+1-212-555-1111>2
From: "Alien Blaster" <sip:B64(SHA-1(555-3333; time=36124172;
seq=74))@localhost>
To: sip:B64(SHA-1(555-3333; time=36124172; seq=75))@localhost
Call-ID: B64(SHA-1(555-1111;time=36124033;seq=72)@localhost
Cseq: 129 INVITE
Referred-by: tel:555-1111
Contact: sip:Host(mta-t2.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
DCS Group Category: Informational - Expiration 8/31/02 145
DCS Architecture February 2002
Upon receiving this INVITE, Proxy-t1 queries the directory server to
determine the IP address (MTA-t1) associated with 212-555-2222. It
then forwards the INVITE message to MTA-t1, after stripping off all
of the billing fields, and adding the encrypted state information.
Remainder of the call completes as shown in Section 10.12.
10.20 Privacy with Application-level Anonymizer
MTA-o ANON-o Proxy-o Proxy-t ANON-t MTA-t
| (1)Invite | | | |
|-------------------->| | | |
| | (2)CREAT | | | |
| |<---------|(4)Invite | (5)CREAT | |
| |-(3)ACK-->|--------->|--------->| |
| | | |<-(6)ACK--| |
| | | |(7)Invite | |
| | | |-------------------->|
| | | | (8) 183 SDP |
| | | |<--------------------|
| | | |(9)MODIFY | |
| | | |--------->| |
| | |(11)183SDP|<-(10)ACK-| |
| |(12)MODIFY|<---------| | |
| |<---------| | | |
|(14)183SDP|-(13)ACK->| | | |
|<--------------------| | | |
|(15)PRACK | (16) PRACK |(17)PRACK |
|--------->|------------------------------->|--------->|
|(20)200 OK| (19) 200 OK |(18)200 OK|
|<---------|<-------------------------------|<---------|
|(21)COMET | (22) COMET |(23)COMET |
|--------->|--------- --------------------->|--------->|
|(26)200 OK| (25) 200 OK |(24)200 OK|
|<---------|----------|----------|----------|----------|
| | | | |(27)180 Rg|
| | |(28) 180 |<--------------------|
| (29)180 Ring |<---------| | |
|<---------|----------| | | |
|(30)PRACK | (31) PRACK |(32)PRACK |
|--------->|------------------------------->|--------->|
|(35)200 OK| (34) 200 OK |(33)200 OK|
|<---------|<-------------------------------|----------|
| | | | | |
| | | | (36) 200 OK |
| | |(37)200 OK|<--------------------|
| (38) 200 OK |<---------| | |
|<--------------------| | | |
|(39) ACK | | (40) ACK | |(41) ACK |
|--------->|--------------------------------|--------->|
| | | | | |
DCS Group Category: Informational - Expiration 8/31/02 146
DCS Architecture February 2002
|<--------------------Active Call-------------------->|
|(42) BYE | |(43) BYE | |(44) BYE |
|--------->|------------------------------->|--------->|
|(47)200 OK| |(46)200 OK| |(45)200 OK|
|<---------|<-------------------------------|<---------|
The call begins identically to that shown in Section 10.1 of a basic
MTA-originated call. The only difference at the originating MTA is
that the Anonymity header is set to "Full" or includes "IPAddr."
(1) INVITE:
INVITE sip:555-2222@Host(DP-o);user=phone SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
Proxy-Require: privacy
Remote-Party-ID: John Doe <tel:555-1111>
Anonymity: Full
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:Host(mta-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuite:312F
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio 3456 RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc- codecs:96
In addition to its normal functions, Proxy-o also checks the
Anonymity indication which is set to "full", so both caller-
id/calling name blocking and IP address privacy must be provided.
Proxy-o therefore contacts the anonymizer to create an anonymous
session:
(2) ANON_Create:
ANON_Create
Endpoint1: Host(mta-o.provider):Port(mta-o.provider)
Endpoint2:
The anonymizer responds back with an anonymizer endpoint address:
(3) ANON_Ack:
DCS Group Category: Informational - Expiration 8/31/02 147
DCS Architecture February 2002
ANON_Ack
AnonAddr: Host(ann-o.provider):Port(ann-o.provider)
The anonymizer implements a packet relay and call signaling gateway
between the two endpoints. The first endpoint specified in the
ANON_Create will receive the anonymizer service. Any packet received
for the anonymizer address specified will be forwarded to Endpoint1.
Any packet sent by Endpoint1 to the anonymizer address will be
forwarded to Endpoint2, but now with a source address of AnonAddr.
Having received the anonymizer address for the call, Proxy-o
generates the following INVITE message and sends it to Proxy-t.
Proxy-omodifies a number of parameters to the INVITE message.
(4) INVITE:
INVITE sip:+1-212-555-2222;rn=+1-212-234-2222;
npdi=yes@Host(dp-t);user=phone SIP/2.0
Via: SIP/2.0/UDP Host(DP-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
Supported: 100rel, state
Require: state
Proxy-Require: dcs, state, privacy
Remote-Party-ID: John Doe; <tel:+1-212-555-1111>
Anonymity: Full
Dcs-Gate: Host(cmts-o.provider):3612/17S30124/37FA1948 required
Dcs-Billing-Info: Host(rks-o.provider)<5123-0123-4567-8900/212-
555-1111/212-555-2222>
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124;
orig-dest=tel:+1-212-555-2222; num-redirects=0
Dcs-Billing-ID: Host(dp-o.provider):36123E5C:0152
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:Host(ann-o.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(ann-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio Port(ann-o) RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
DCS Group Category: Informational - Expiration 8/31/02 148
DCS Architecture February 2002
Proxy-t also checks the Anonymity indication which is set to "full",
so both caller-id/calling name blocking and IP address privacy must
be provided. We furthermore assume, that MTA-t has requested
privacy, i.e. the originating party must not be able to tell the IP-
address of MTA-t. Proxy-t therefore contacts an anonymizer to create
an anonymous session:
(5) ANON_Create:
ANON_Create
Endpoint1:
Endpoint2: Host(ann-o.provider):Port(ann-o.provider)
The anonymizer responds back with an anonymizer endpoint address:
(6) ANON_Ack:
ANON_Ack
AnonAddr: Host(ann-t.provider):Port(ann-t.provider)
The anonymizer implements a packet relay and call signaling gateway
between the two endpoints. The first endpoint specified in the
ANON_Create will receive the anonymizer service. Any packet received
for the anonymizer address specified will be forwarded to Endpoint1.
Any packet sent by Endpoint1 to the anonymizer address will be
forwarded to Endpoint2, but now with a source address of AnonAddr.
Proxy-t now generates the following INVITE message and sends it to
MTA-t.
(7) INVITE:
INVITE sip:555-2222@Host(mta-t.provider); user=phone SIP/2.0
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
Supported: 100rel, state
Require: state
Remote-Party-ID: <sip:{type=remote-id; orig=tel:+1-212-555-
1111; anonymity=full}K@Host(dp-t.provider);
user=private>; rpi-id=private
Media-Authorization: 31S14621
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Contact: sip:Host(ann-t.provider):Port(ann-t.provider)
Content-Type: application/sdp
Content-length: (.)
DCS Group Category: Informational - Expiration 8/31/02 149
DCS Architecture February 2002
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(ann-t.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
a=rtpmap:96 G726-32/8000
m=audio Port(ann-t.provider) RTP/AVP 0
a=qos:mandatory sendrecv
a=X-pc-codecs:96
Upon receiving this INVITE, MTA-t authenticates that the message
came from Proxy-t using IPSec. MTA-t checks the telephone line
associated with the E.164-t to see if it is available. If it is
available, MTA-t looks at the capability parameters in the Session
Description Protocol (SDP) part of the message and determines which
media channel parameters it can accommodate for this call. MTA-t
stores the INVITE message, including the encrypted State parameters,
for later use. MTA-t puts this line in the "busy" state (so any
other call attempts are rejected until this call clears), generates
the following 183-Session-Progress response, and sends it to Proxy-
t. MTA-t starts timer (T-proxy-response).
(8) 183-Session-Progress:
SIP/2.0 183 Session Progress
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
Require: 100rel
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
Remote-Party-ID: John Smith <tel:555-2222>
Anonymity: full
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Rseq: 9021
Content-Disposition: precondition
Contact: sip:Host(mta-t.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
DCS Group Category: Informational - Expiration 8/31/02 150
DCS Architecture February 2002
c= IN IP4 Host(mta-t.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=rtpmap:0 PCMU/8000
m=audio 6544 RTP/AVP 0
a=qos:mandatory sendrecv confirm
Upon receiving the 183-Session-Progress message, Proxy-t updates the
anonymizer with the MTA-t address information:
(9) ANON_Modify:
ANON_Modify
Endpoint1: Host(mta-t.provider):Port(mta-t.provider)
Endpoint2: Host(ann-o.provider):Port(ann-o.provider)
The anonymizer responds back:
(10) ANON_Ack:
ANON_Ack
Following the anonymizer update, Proxy-t then forwards the following
183-Session-Progress message to Proxy-o, restoring the Via headers,
and adding Dcs-Gate information. At this point Proxy-t has
completed its transaction and does not maintain any more state for
this call, processing all further signaling messages as a stateless
proxy.
(11) 183-Session-Progress:
SIP/2.0 183 Session Progress
Via: SIP/2.0/UDP Host(dp-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
Require: 100rel
State: Host(dp-t.provider); nexthop=sip:555-2222@Host(mta-
t.provider); gate=Host(cmts-t.provider):4321/31S14621
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124;
orig-dest=tel:+1-212-555-2222; num-redirects=0
Dcs-Gate: Host(cmts-t.provider):4321/31S14621/37FA1948
Remote-Party-ID: John Smith <tel:+1-212-555-2222>
Anonymity: full
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Rseq: 9021
Content-Disposition: precondition
Contact: sip:Host(ann-t.provider):Port(ann-t.provider)
Content-Type: application/sdp
Content-length: (.)
v=0
DCS Group Category: Informational - Expiration 8/31/02 151
DCS Architecture February 2002
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(ann-t.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=rtpmap:0 PCMU/8000
m=audio Port(ann-t.provider) RTP/AVP 0
a=qos:mandatory sendrecv confirm
Upon receiving the 183-Session-Progress message, Proxy-o informs the
originating anonymizer about the second endpoint:
(12) ANON_Modify:
ANON_Modify
Endpoint1: Host(mta-o.provider):Port(mta-o.provider)
Endpoint2: Host(ann-t.provider) :Port(ann-t.provider)
The anonymizer responds back:
(13) ANON_Ack:
ANON_Ack
Subsequently, Proxy-o forwards the following 183-Session-Progress to
MTA-o. At this point Proxy-o has completed its transaction and does
not maintain any more state for this call, processing all further
signaling messages as a stateless proxy.
(14) 183-Session-Progress:
SIP/2.0 183 Session Progress
Via: Sip/2.0/UDP Host(mta-o.provider)
Require: 100rel
Media-Authorization: 17S30124
State: Host(dp-o.provider); state="{gate= Host(cmts-
o.provider): 3612/17S30124, nexthop=sip:+1-212-555-
2222;rn=+1-212-234-2222@Host(DP-t), state="Host(dp-
t.provider); nexthop=sip:555-2222@Host(mta-t.provider);
gate=Host(cmts-t.provider):4321/31S14621; orig-
dest=tel:+1-212-555-1111; num-redirects=0"}K"
Remote-Party-ID: <sip:{type=remote-id; orig=tel:+1-212-555-
2222; anonymity=full}K@Host(dp-t.provider);
user=private>; rpi-id=private
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Rseq: 9021
Content-Disposition: precondition
Contact: sip:Host(ann-o.provider):Port(ann-o.provider)
Content-Type: application/sdp
Content-length: (.)
DCS Group Category: Informational - Expiration 8/31/02 152
DCS Architecture February 2002
v=0
o=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(ann-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio Port(ann-o) RTP/AVP 0
a-X=pc-qos:mandatory sendrecv confirm
Upon receiving the 183-Session-Progress message, MTA-o sends the
following PRACK message indirectly to MTA-t through the anonymizer
using the IP address in the Contact header of the 183-Session-
Progress message.
(15) PRACK:
PRACK sip:Host(ann-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 128 PRACK
Rack: 9021 127 INVITE
Content-Type: application/sdp
Content-length: (.)
v=0
O=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 3456 RTP/AVP 0
a-qos:mandatory sendrecv
ANN-o modifies the address information in the message and forwards
it to ANN-t.
(16) PRACK:
PRACK sip:Host(ann-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(ann-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 128 PRACK
Rack: 9021 127 INVITE
DCS Group Category: Informational - Expiration 8/31/02 153
DCS Architecture February 2002
Content-Type: application/sdp
Content-length: (.)
v=0
O=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(ann-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio Port(ann-o.provider) RTP/AVP 0
a-qos:mandatory sendrecv
ANN-t modifies the address information in the message and forwards
it to MTA-t.
(17) PRACK
PRACK sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(ann-t.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 128 PRACK
Rack: 9021 127 INVITE
Content-Type: application/sdp
Content-length: (.)
v=0
O=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(ann-t.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio Port(ann-t.provider) RTP/AVP 0
a-qos:mandatory sendrecv
MTA-t acknowledges the PRACK with a 200-OK, and begins to reserve
the resources necessary for the call.
(18) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(ann-t.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 128 PRACK
DCS Group Category: Informational - Expiration 8/31/02 154
DCS Architecture February 2002
ANN-t modifies the address information in the message and forwards
it to ANN-o.
(19) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(ann-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 128 PRACK
ANN-o modifies the address information in the message and forwards
it to MTA-o.
(20) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 128 PRACK
After sending PRACK(7), MTA-o attempts to reserve network resources
if necessary. If resource reservation is successful, MTA-o sends
the following COMET message directly to MTA-t. MTA-o starts timer
(T-direct-request).
(21) COMET:
COMET sip:Host(ann-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 COMET
Content-Type: application/sdp
Content-length: (.)
v=0
O=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(mta-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio 3456 RTP/AVP 0
a=qos:success send
DCS Group Category: Informational - Expiration 8/31/02 155
DCS Architecture February 2002
ANN-o modifies the address information in the message and forwards
it to ANN-t.
(22) COMET:
COMET sip:Host(ann-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(ann-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 COMET
Content-Type: application/sdp
Content-length: (.)
v=0
O=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(ann-o.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio Port(ann-o.provider) RTP/AVP 0
a=qos:success send
ANN-t modifies the address information in the message and forwards
it to MTA-t.
(23) COMET:
COMET sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(ann-t.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 COMET
Content-Type: application/sdp
Content-length: (.)
v=0
O=- 2987933615 2987933615 IN IP4 A3C47F2146789F0
s=-
c= IN IP4 Host(ann-t.provider)
b=AS:64
t=907165275 0
a=X-pc-csuites:312F
a=X-pc-secret:clear:WhenInTheCourseOfHumanEvents
a=rtpmap:0 PCMU/8000
m=audio Port(ann-t.provider) RTP/AVP 0
a=qos:success send
MTA-t acknowledges the COMET message with a 200-OK.
DCS Group Category: Informational - Expiration 8/31/02 156
DCS Architecture February 2002
(24) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(ann-t.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 COMET
ANN-t modifies the address information in the message and forwards
it to ANN-o.
(25) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(ann-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 COMET
ANN-o modifies the address information in the message and forwards
it to MTA-o.
(26) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 129 COMET
Upon receipt of the 200-OK(26), MTA-o stops timer (T-direct-
request).
Upon receipt of the (17) PRACK message, MTA-t stops timer (T-proxy-
response) and attempts to reserve network resources if necessary.
Once MTA-t both receives the COMET message and has successfully
reserved network resources, MTA-t begins to send ringing voltage to
the designated line and sends the following 180 RINGING message
through Proxy-t. MTA-t restarts the session timer (T3) with value
(T-ringing).
(27) 180 RINGING:
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
Require: 100rel
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
DCS Group Category: Informational - Expiration 8/31/02 157
DCS Architecture February 2002
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Contact: sip:Host(mta-t.provider)
Cseq: 127 INVITE
Rseq: 9022
Proxy-t decodes the Via: headers, and passes the 180-Ringing to
Proxy-o. This operation is done as a SIP stateless proxy.
(28) 180 RINGING:
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP Host(dp-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
Require: 100rel
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Contact: sip:Host(ann-t.provider):Port(ann-t.provider)
Cseq: 127 INVITE
RSeq: 9022
Proxy-o handles the message as a SIP stateless proxy, and passes the
180-Ringing to MTA-o.
(29) 180 RINGING:
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP Host(mta-o.provider)
Require: 100rel
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Contact: sip:Host(ann-o.provider):Port(ann-o.provider)
Cseq: 127 INVITE
RSeq: 9022
Upon receipt of the 180 RINGING message, MTA-o restarts the
transaction timer (T3) with value (T-ringing). MTA-o acknowledges
the provisional response with a PRACK, and plays audible ringback
tone to the customer.
(30) PRACK:
PRACK sip:Host(ann-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
DCS Group Category: Informational - Expiration 8/31/02 158
DCS Architecture February 2002
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 130 PRACK
RAck: 9022 127 INVITE
ANN-o modifies the address information in the message and forwards
it to ANN-t.
(31) PRACK:
PRACK sip:Host(ann-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(ann-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 130 PRACK
RAck: 9022 127 INVITE
ANN-t modifies the address information in the message and forwards
it to MTA-t.
(32) PRACK:
PRACK sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(ann-t.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 130 PRACK
RAck: 9022 127 INVITE
MTA-t acknowledges the PRACK with a 200-OK, and stops timer (T-
proxy-response).
(33) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(ann-t.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 130 PRACK
ANN-t modifies the address information in the message and forwards
it to ANN-o.
(34) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(ann-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
DCS Group Category: Informational - Expiration 8/31/02 159
DCS Architecture February 2002
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 130 PRACK
ANN-o modifies the address information in the message and forwards
it to MTA-o.
(35) 200 OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 130 PRACK
Once MTA-t detects off-hook on the called line, it disconnects
ringing voltage from the line and sends the final response through
the proxies. MTA-t stops timer (T-ringing) and starts timer (T-
proxy-response). If necessary, MTA-t may also commit to resources
that have been reserved for this call. At this point, MTA-t begins
to generate bearer channel packets of encoded voice and send them to
MTA-o using the IP address and port number specified in the SDP part
of the original INVITE message.
(36) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(dp-t.provider), {via="Host(dp-
o.provider); branch=1"; via=Host(mta-o.provider)}K
State: Host(dp-t.provider); state="{nexthop=sip:Host(dp-
o.provider); gate=Host(cmts-t.provider):4321/31S14621;
state="Host(dp-o.provider); nexthop=sip:555-
1111@Host(mta-o.provider); gate=Host(cmts-
o.provider):3612/17S30124; orig-dest=tel:+1-212-555-
2222; num-redirects=0"}K"
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Proxy-t handles the message as a SIP stateless proxy, and forwards
it to Proxy-o.
(37) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(dp-o.provider);branch=1
Via: SIP/2.0/UDP Host(mta-o.provider)
State: Host(dp-o.provider); nexthop=sip:555-1111@Host(mta-
o.provider); gate=Host(cmts-o.provider):3612/17S30124
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
DCS Group Category: Informational - Expiration 8/31/02 160
DCS Architecture February 2002
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Proxy-o handles the message as a SIP stateless proxy, and forwards
it to MTA-o.
(38) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 INVITE
Upon receipt of the 200-OK message, MTA-o stops timer (T-ringing)
and stops playing audible ringback tone to the customer and begins
to play the bearer channel stream that is received from MTA-t. MTA-
o sends the following ACK message to MTA-t. If necessary, MTA-o may
also commit to resources that have been reserved for this call. At
this point, MTA-o begins to generate bearer channel packets of
encoded voice and send them to MTA-t using the IP address and port
number specified in the SDP part of the original 183-Session-
Progress message (that was a response to the original INVITE).
(39) ACK:
ACK sip:Host(ann-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 ACK
ANN-o modifies the address information in the message and forwards
it to ANN-t.
(40) ACK:
ACK sip:Host(ann-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(ann-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 ACK
ANN-t modifies the address information in the message and forwards
it to MTA-t.
(41) ACK:
ACK sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(ann-t.provider)
DCS Group Category: Informational - Expiration 8/31/02 161
DCS Architecture February 2002
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 127 ACK
Upon receipt of the ACK message, MTA-t stop timer (T-proxy-
response).
When either MTA detects hangup, it sends out a BYE message to the
other MTA. In this example, MTA-o detected that the customer hung
up the phone. MTA-o puts that line in the "idle" state so new calls
can be made or received. It sends the following BYE message
directly to MTA-t. MTA-o may also need to release network resources
that have been used for the call. MTA-o starts timer (T-direct-
request).
(42) BYE:
BYE sip:Host(ann-o.provider) SIP/2.0
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 131 BYE
ANN-o modifies the address information in the message and forwards
it to ANN-t.
(43) BYE:
BYE sip:Host(ann-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(ann-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 131 BYE
ANN-t modifies the address information in the message and forwards
it to MTA-t.
(44) BYE:
BYE sip:Host(mta-t.provider) SIP/2.0
Via: SIP/2.0/UDP Host(ann-t.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 131 BYE
Upon receipt of the BYE message, MTA-t stops playing the bearer
channel stream received from MTA-o and, if necessary, releases
network resources that have been used for this call. MTA-tsends the
DCS Group Category: Informational - Expiration 8/31/02 162
DCS Architecture February 2002
following 200-OK message to MTA-o. MTA-t starts a 15-second timer
(T-hangup) (Note: this is a local interface issue, and not part of
this specification). If MTA-t does not detect hangup on the line
before timer (T-hangup) expires, it plays "reorder" tone on the
customer line. Once hangup is detected, MTA-t puts that line in the
"idle" state so new calls can be made or received.
(45) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(ann-t.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 131 BYE
ANN-t modifies the address information in the message and forwards
it to ANN-o.
(46) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(ann-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 131 BYE
ANN-o modifies the address information in the message and forwards
it to MTA-o.
(47) 200-OK:
SIP/2.0 200 OK
Via: SIP/2.0/UDP Host(mta-o.provider)
From: "Alien Blaster" <sip:B64(SHA-1(555-1111; time=36123E5B;
seq=72))@localhost>
To: sip:B64(SHA-1(555-2222; time=36123E5B; seq=73))@localhost
Call-ID: B64(SHA-1(555-1111;time=36123E5B;seq=72))@localhost
Cseq: 131 BYE
Upon receipt of 200-OK, MTA-o stops timer (T-direct-request).
11. Notice Regarding Intellectual Property Rights
The IETF has been notified of intellectual property rights claimed
in regard to some or all of the specification contained in this
document. For more information consult the online list of claimed
rights.
12. References
DCS Group Category: Informational - Expiration 8/31/02 163
DCS Architecture February 2002
1. Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996.
2. Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
3. "SIP Extensions for Caller Identity, Privacy and Operator
Services", Internet Draft: <draft-ietf-sip-privacy-00.txt>,
November 2000.
4. "SIP proxy-to-proxy extensions for supporting Distributed Call
State", Internet Draft: <draft-dcsgroup-sip-proxy-proxy-03.txt>,
November 2000.
5. "SIP extensions for supporting Distributed Call State", Internet
Draft: <draft-ietf-sip-state-00.txt>, November 2000.
6. "SIP Extensions for Media Authorization", Internet Draft: <draft-
ietf-sip-call-auth-00.txt>, November 2000.
7. "Reliability of Provisional Responses in SIP", Internet Draft:
<draft-ietf-sip-100rel-02.txt>, July, 2000.
8. "SIP 183 Session Progress Message", Internet Draft: <draft-ietf-
sip-183-00.txt>, October 1999.
9. "Integration of Resource Management and SIP for IP Telephony",
Internet Draft: <draft-ietf-sip-manyfolks-resource-00.txt>,
November 2000.
13. Acknowledgements
The Distributed Call Signaling work in the PacketCable project is
the work of a large number of people, representing many different
companies. The authors would like to recognize and thank the
following for their assistance: John Wheeler, Motorola; David
Boardman, Daniel Paul, Arris Interactive; Bill Blum, Jon Fellows,
Jay Strater, Jeff Ollis, Clive Holborow, Motorola; Doug Newlin,
Guido Schuster, Ikhlaq Sidhu, 3Com; Jiri Matousek, Bay Networks;
Farzi Khazai, Nortel; John Chapman, Bill Guckel, Michael Ramalho,
Cisco; Chuck Kalmanek, Doug Nortz, John Lawser, James Cheng, Tung-
Hai Hsiao, Partho Mishra, AT&T; Telcordia Technologies; and Lucent
Cable Communications.
14. Author's Addresses
Bill Marshall
AT&T
Florham Park, NJ 07932
DCS Group Category: Informational - Expiration 8/31/02 164
DCS Architecture February 2002
Email: wtm@research.att.com
K. K. Ramakrishnan
TeraOptic Networks
Sunnyvale, CA
Email: kk@teraoptic.com
Ed Miller
Terayon
Louisville, CO 80027
Email: edward.miller@terayon.com
Glenn Russell
CableLabs
Louisville, CO 80027
Email: G.Russell@Cablelabs.com
Matt Osman
CableLabs
Louisville, CO 80027
Email: M.Osman@Cablelabs.com
Burcak Beser
Juniper Networks
Sunnyvale, CA
Email: burcak@juniper.net
Mike Mannette
3Com
Rolling Meadows, IL 60008
Email: Michael_Mannette@3com.com
Kurt Steinbrenner
3Com
Rolling Meadows, IL 60008
Email: Kurt_Steinbrenner@3com.com
Dave Oran
Cisco
Acton, MA 01720
Email: oran@cisco.com
Flemming Andreasen
Cisco
Edison, NJ
Email: fandreas@cisco.com
John Pickens
Com21
San Jose, CA
Email: jpickens@com21.com
Poornima Lalwaney
DCS Group Category: Informational - Expiration 8/31/02 165
DCS Architecture February 2002
Nokia
San Diego, CA 92121
Email: poornima.lalwaney@nokia.com
Jon Fellows
Copper Mountain Networks
San Diego, CA 92121
Email: jfellows@coppermountain.com
Doc Evans
D. R. Evans Consulting
Boulder, CO 80303
Email: n7dr@arrl.net
Keith Kelly
NetSpeak
Boca Raton, FL 33587
Email: keith@netspeak.com
DCS Group Category: Informational - Expiration 8/31/02 166
DCS Architecture February 2002
Full Copyright Statement
"Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English. The limited permissions granted above are perpetual and
will not be revoked by the Internet Society or its successors or
assigns. This document and the information contained herein is
provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."
This memo is filed as <draft-dcsgroup-sip-arch-06.txt>, and expires
August 31, 2002.
DCS Group Category: Informational - Expiration 8/31/02 167
