Internet DRAFT - draft-dcsgroup-sip-proxy-proxy
draft-dcsgroup-sip-proxy-proxy
SIP Working Group W. Marshall
Internet Draft AT&T
Document: <draft-dcsgroup-sip-proxy-proxy-06.txt>
Category: Informational K. Ramakrishnan
TeraOptic Networks
E. Miller
Terayon Networks
G. Russell
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
SIP proxy-to-proxy extensions for supporting DCS
Status of this Memo
This document is an Internet-Draft and is in full compliance with
all provisions of Section 10 of RFC2026[1].
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SIP Proxy-to-Proxy Extensions February 2002
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1. Abstract
In order to deploy a residential telephone service at very large
scale across different domains, it is necessary for trusted elements
owned by different service providers to exchange trusted information
that conveys customer-specific information and expectations about
the parties involved in the call. This document describes extensions
to the Session Initiation Protocol (RFC2543) for supporting the
exchange of customer information and billing information between
trusted entities in the architecture described in <draft-dcsgroup-
sip-arch-02.txt>.
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].
3. Table of Contents
Status of this Memo................................................1
1. Abstract........................................................2
2. Conventions used in this document...............................2
3. Table of Contents...............................................2
4. Introduction....................................................3
5. Trust Boundary..................................................5
6. Requires and Supported Option Tag Values........................6
7. DCS-TRACE-PARTY-ID..............................................7
7.1 Syntax.........................................................7
7.2 Procedures at an Untrusted User Agent Client (UAC).............7
7.3 Procedures at a Trusted User Agent Client (UAC)................7
7.4 Procedures at an Untrusted User Agent Server (UAS).............8
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7.5 Procedures at a Trusted User Agent Server (UAS)................8
7.6 Procedures at Proxy............................................8
7.6.1 Procedures at Originating Proxy..............................8
7.6.2 Procedures at Terminating Proxy..............................8
8. DCS-GATE........................................................8
8.1 Syntax.........................................................9
8.2 Procedures at an Untrusted User Agent Client (UAC).............9
8.3 Procedures at a Trusted User Agent Client (UAC)................9
8.4 Procedures at an Untrusted User Agent Server (UAS)............10
8.5 Procedures at a Trusted User Agent Server (UAS)...............10
8.6 Procedures at Proxy...........................................10
8.6.1 Procedures at Originating Proxy.............................10
8.6.2 Procedures at Terminating Proxy.............................11
9. DCS-OSPS.......................................................11
9.1 Syntax........................................................11
9.2 Procedures at an Untrusted User Agent Client (UAC)............12
9.3 Procedures at a Trusted User Agent Client (UAC)...............12
9.4 Procedures at an Untrusted User Agent Server (UAS)............12
9.5 Procedures at a Trusted User Agent Server (UAS)...............13
9.6 Procedures at Proxy...........................................13
10. DCS-BILLING-ID and DCS-BILLING-INFO...........................13
10.1 Syntax.......................................................15
10.2 Procedures at an Untrusted User Agent Client (UAC)...........16
10.3 Procedures at a Trusted User Agent Client (UAC)..............16
10.4 Procedures at an Untrusted User Agent Server (UAS)...........16
10.5 Procedures at a Trusted User Agent Server (UAS)..............17
10.6 Procedures at Proxy..........................................17
10.6.1 Procedures at Originating Proxy............................17
10.6.2 Procedures at Terminating Proxy............................18
11. DCS-LAES and DCS-REDIRECT.....................................19
11.1 Syntax.......................................................19
11.2 Procedures at an Untrusted User Agent Client (UAC)...........19
11.3 Procedures at a Trusted User Agent Client (UAC)..............20
11.4 Procedures at an Untrusted User Agent Server (UAS)...........20
11.5 Procedures at a Trusted User Agent Server (UAS)..............20
11.6 Procedures at Proxy..........................................21
11.6.1 Procedures at Originating Proxy............................21
11.6.2 Procedures at Terminating Proxy............................23
12. Security Considerations.......................................23
13. Notice Regarding Intellectual Property Rights.................23
14. References....................................................24
15. Acknowledgements..............................................24
16. Author's Addresses............................................24
Full Copyright Statement..........................................27
4. Introduction
In order to deploy a residential telephone service at very large
scale across different domains, it is necessary for trusted elements
owned by different service providers to exchange trusted information
that conveys billing information and expectations about the parties
involved in the call.
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There are many billing models used in deriving revenue from
telephony services today. Charging for telephony services is tightly
coupled to the use of network resources. It is outside the scope of
this document to discuss the details of these numerous and varying
methods.
A key motivating principle of the DCS architecture described in [3]
is the need for network service providers to be able to control and
monitor network resources; revenue may be derived from the usage of
these resources as well as from the delivery of enhanced services
such as telephony. Furthermore, the DCS architecture recognizes the
need for coordination between call signaling and resource
management. This coordination ensures that users are authenticated
and authorized before receiving access to network resources and
billable enhanced services.
DCS-Proxies, as defined in [3], have access to subscriber
information and act as policy decision points and trusted
intermediaries along the call signaling path. Edge routers provide
the policy enforcement mechanism and also capture and report usage
information. Edge routers need to be given billing information that
can be logged with Record Keeping or Billing servers. The DCS
Proxy, as a central point of coordination between call signaling and
resource management, can provide this information based on the
authenticated identity of the calling and called parties. Since
there is a trust relationship among DCS Proxies, they can be relied
upon to exchange trusted billing information pertaining to the
parties involved in a call.
For these reasons, it is appropriate to consider defining SIP header
extensions to allow DCS Proxies to exchange information during call
setup. It is the intent that the extensions would only appear on
trusted network segments, should be inserted upon entering a trusted
network region, and removed before leaving trusted network segments.
Rules for inserting and removing headers exchanged only between
proxies are for further study.
Significant amounts of information is retrieved by an originating
proxy in its handling of a connection setup request from a user
agent. Such information includes location information about the
subscriber (essential for emergency services calls), billing
information, and station information (e.g. coin operated phone). In
addition, while translating the destination number, information such
as the local-number-portability office code is obtained and will be
needed by all other proxies handling this call.
For Usage Accounting records, it is necessary to have an identifier
that can be associated with all the event records produced for the
call. Call-ID cannot be used as such an identifier since it is
selected by the originating user agent, and may not be unique among
all past calls as well as current calls. Further, since this
identifier is to be used by the service provider, it should be
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chosen in a manner and in a format that meets the service provider's
needs.
Billing information may not necessarily be unique for each user
(consider the case of calls from an office all billed to the same
account). Billing information may not necessarily be identical for
all calls made by a single user (consider prepaid calls, credit card
calls, collect calls, etc). It is therefore necessary to carry
billing information separate from the calling and called party
identification. Furthermore, some billing models call for split-
charging where multiple entities are billed for portions of the
call.
The addition of two SIP General Header Fields allows for the capture
of billing information and billing identification for the duration
of the call. Alternative techniques such as multi-part attachments
will not coexist with encrypted messages.
It is the intent that the billing extensions would only appear on
trusted network segments, and MAY be inserted by a DCS Proxy in
INVITE requests entering a trusted network segment, and removed
before leaving trusted network segments.
5. 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 User Agent (UA) may be either within the trust boundary or
outside the trust boundary, depending on exactly what function is
being performed and exactly how it is being performed.
Accordingly, the procedures followed by a User Agent are different
depending on whether the UA is within the trust boundary or outside
the trust boundary.
The following sections giving procedures for User Agents therefore
are subdivided into trusted user agents and untrusted user agents.
A trusted user agent is, in almost all cases, equivalent to the
combination of an untrusted user agent and a proxy.
6. Requires and Supported Option Tag Values
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UACs which support one or more of the extensions defined here
include a Supported header in all requests, except ACK, with the
option tag according to the following table:
Extension Headers Supported Option tag
DCS-Trace-Party-ID DCS.Trace
DCS-Gate DCS.Gate
DCS-OSPS DCS.OSPS
DCS-Billing-ID and DCS-Billing-Info DCS.Billing
DCS-LAES and DCS-Redirect DCS.Laes
All of the above DCS
Proxies on the signaling path may have their own requirements for
the extensions defined in this document. If the Supported header in
the request lists the option tag value given above, a proxy can be
certain the UAC understands the extension headers corresponding to
that tag value. If, however, the Supported header was absent, or was
present but didn't include the desired tag value, the proxy MAY
reject the request with a 421, and indicate in the Require header
that one or more of the features are needed. As an alternative, the
proxy MAY forward the request, but MUST NOT add any extensions
defined in this document. This will allow the call to proceed
without the extensions.
If a proxy wishes to ensure that the UAS understands the extensions
described in this document, it MAY add a Requires header to the
request with the option tag value as given above. If a proxy wishes
to ensure that other proxies understand the extensions described in
this document, it MAY add a Proxy-Requires header to the request
with the option tag value as given above.
If a proxy receives a request with a Proxy-Requires header with an
option tag value given above, but does not support the extensions
described in this document for that tag value, it MUST reject the
request with a 421.
If the UAS receives a request with a Requires header with an option
tag value given above, but does not support the extensions described
in this document for that tag value, it MUST reject the request with
a 421.
If a proxy or UAS receives a request with a Supported header with an
option tag value given above, and uses the extensions described in
this document in the response, it MUST include a Require header in
the response, with the appropriate tag value, indicating that the
feature was applied to the response.
7. DCS-TRACE-PARTY-ID
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In the telephone network, calling identity information is used to
support regulatory requirements such as the Customer Originated
Trace service, which provide the called party with the ability to
report obscene or harassing phone calls to law enforcement. This
service is provided independent of caller-id, and operates even if
the caller requested anonymity. The calling party is here
identified as the station originating the call. In order for this
service to be dependable, the called party must be able to trust
that the calling identity information being presented is valid.
To initiate a customer-originated-trace from an untrusted UAC, an
additional header is defined for the INVITE request sent from the
untrusted UAC to its proxy. This header is called Dcs-Trace-Party-
ID, and does not appear in any other request or response. The proxy
receiving a properly formed INVITE request with this header performs
the service-provider-specific functions of recording and reporting
the caller identity for law enforcement action. The proxy then
completes the call to either an announcement server or to the
service-provider's business office to collect further information
about the complaint. A trusted UAC does not use this header, as it
initiates this action locally.
7.1 Syntax
The BNF description of this header is:
Dcs-Trace-Party-ID = "Dcs-Trace-Party-ID" ":" "<" addr-spec ">"
Addr-spec contains a URL that identifies the remote endpoint. Addr-
spec typically contains a tel: URL giving the identity of the remote
endpoint, or a DCS-URL with a private-param when privacy was
requested by the remote endpoint. This URL SHOULD be the value
received in the Remote-Party-ID header of the harassing call.
7.2 Procedures at an Untrusted User Agent Client (UAC)
The UAC MUST insert a Dcs-Trace-Party-ID header into the initial
INVITE message for a customer-originated-trace request. The UAC
MUST use a Request-URI with username of "call-trace" and host
identifying the provisioned proxy for the untrusted UA.
7.3 Procedures at a Trusted User Agent Client (UAC)
A trusted UAC performs the customer-originated-trace in a manner
similar to the originating proxy, described below. A trusted UAC
MUST NOT include this header in any request.
7.4 Procedures at an Untrusted User Agent Server (UAS)
This header MUST NOT appear in any response sent by a UAS.
7.5 Procedures at a Trusted User Agent Server (UAS)
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This header MUST NOT appear in any request sent by a UAS.
7.6 Procedures at Proxy
Two sets of proxy procedures are defined: (1) the procedures at an
originating proxy, and (2) the procedures at a terminating proxy.
The originating proxy is a proxy that received the INVITE request
from a non-trusted endpoint.
The terminating proxy is a proxy that sends the INVITE request to a
non-trusted endpoint.
A proxy that both receives the INVITE request from an untrusted
endpoint, and sends the INVITE request to an untrusted endpoint,
performs both sets of procedures.
7.6.1 Procedures at Originating Proxy
If the Dcs-Trace-Party-ID header is present in the initial INVITE
request from the UAC, and the Request-URI of the INVITE has username
of "call-trace" and host of the originating proxy, the originating
proxy MUST perform the service-provider-specific functions of
recording and reporting the caller identity for law enforcement
action. The proxy then MUST direct the call to either an
announcement server or to the service-provider's business office to
collect further information about the complaint.
The originating proxy MUST remove the Dcs-Trace-Party-ID header from
the INVITE before sending the request to another proxy or UAS.
7.6.2 Procedures at Terminating Proxy
This header MUST NOT appear in any request or response sent by a
proxy.
8. DCS-GATE
The Dcs-Gate header extension is used only on requests and responses
between proxies. It never is sent to, nor sent by, an untrusted
UAC/UAS.
The proxy-proxy signaling establishes a synchronization path that
may be required by the PacketCable Dynamic Quality of Service (D-
QoS) specification to coordinate the release of resources of the
call. As per the D-QoS specification, the CMTS monitors the packet
flow, and generates a Gate-Close message in response to either an
explicit close request from the MTA/RGW, or when an equipment or
facility failure causes the connection to be broken. This Gate-Close
message is directed either to the local CMS/Agent, or to the remote
CMS/Agent, or to the CMTS serving the remote MTA, depending on the
capabilities of the endpoints. When a CMS/Agent receives such a
Gate-Close message, it considers it identical to a call termination
request.
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The Dcs-Gate header is used between proxies, and conveys the
location of the remote gate, identity of the gate, and the security
key to be used in gate coordination messages.
8.1 Syntax
The BNF description of the Dcs-Gate header is as follows:
Dcs-Gate = "Dcs-Gate" ":" hostport "/" Gate-ID
[";" Gate-Key ";" Gate-CipherSuite]
[Gate-strength-token]
Gate-ID = 1*alphanum
Gate-Key = 1*alphanum
Gate-CipherSuite = token
Gate-strength-token = "required" | "optional"
Hostport gives the IP address or FQDN of the CMTS/EdgeRouter that
enforces the QoS, or the endpoint system that simulates the gate
coordination exchange on behalf of an edge router.
Gate-ID is a token used at the system named in the Hostport
parameter to identify the particular session. For DCS systems, it
is a 32-bit quantity encoded as an 8-character string of digits 0-9
and letters a-f.
Gate-Key is a character string that provides keying information to
the system named in the hostport parameter. The method of deriving
the actual keys for the gate coordination messages, and the security
procedures, are beyond the scope of this document.
Gate-CipherSuite is a character string that gives the type of
encryption algorithm that will be used to secure the gate
coordination messages.
Gate-Strength-Token specifies whether the gate coordination is
required or optional for the current session. Its use is described
in the following sections.
8.2 Procedures at an Untrusted User Agent Client (UAC)
This header is never sent to an untrusted UAC, and is never sent by
an untrusted UAC.
8.3 Procedures at a Trusted User Agent Client (UAC)
A UAC located within the trust boundary of the service provider
performs the functions given in section 7.6.1.
8.4 Procedures at an Untrusted User Agent Server (UAS)
This header is never sent to an untrusted UAS, and is never sent by
an untrusted UAS.
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8.5 Procedures at a Trusted User Agent Server (UAS)
A UAS located within the trust boundary of the service provider
performs the functions given in section 7.6.2.
8.6 Procedures at Proxy
The Dcs-Gate header MUST NOT appear in any message other than the
initial INVITE request, or in the first non-100 response to that
request. The proxy MUST remove the Dcs-Gate header in any request
or response sent to an untrusted endpoint.
Two sets of proxy procedures are defined: (1) the procedures at an
originating proxy, and (2) the procedures at a terminating proxy.
The originating proxy is a proxy that received the INVITE request
from a non-trusted endpoint.
The terminating proxy is a proxy that sends the INVITE request to a
non-trusted endpoint.
A proxy that both receives the INVITE request from an untrusted
endpoint, and sends the INVITE request to a non-trusted endpoint,
does not generate a Dcs-Gate header.
A proxy that is neither an originating proxy nor a terminating proxy
has no function in coordinating the commitment of resources.
8.6.1 Procedures at Originating Proxy
The originating proxy MUST insert a Dcs-Gate header in the initial
INVITE message for a new call.
The originating proxy MUST identify the system that will perform
gate coordination (either the proxy itself, or the CMTS controlling
the media flow to the endpoint), and the identification token used
at that system to identify the call. It MUST insert the IP address
or FQDN of that system in the hostport parameter of the Dcs-Gate
header, and the identification token as the Gate-ID.
The originating proxy MUST pick a security key and cipher suite for
the gate coordination message exchange, and insert these values in
the Dcs-Gate header.
If the system that will perform gate coordination is a CMTS, the
strength token MUST be given as required. If the system that will
perform gate coordination is the proxy itself, the strength token
MAY be given as optional, or omitted.
8.6.2 Procedures at Terminating Proxy
The terminating proxy MUST identify the system that will perform
gate coordination (either the proxy itself, or the CMTS controlling
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the media flow to the endpoint), and the identification token used
at that system to identify the call. Gate coordination will be
required for this call if (1) the strength token in the Dcs-Gate
header in the initial INVITE indicates 'required', or (2) the system
that will perform gate coordination at the destination is a CMTS.
If gate coordination is required for this call, the terminating
proxy MUST include a Dcs-Gate header in the first non-100 response
to the initial INVITE request. It MUST insert the IP address or
FQDN of the system that will perform gate coordination in the
hostport parameter of the Dcs-Gate header, and the identification
token as the Gate-ID.
If gate coordination is not required for this call, the terminating
proxy SHOULD NOT include a Dcs-Gate header in the first non-100
response to the initial INVITE request.
9. DCS-OSPS
Some calls have special call processing requirements that may not be
satisfied by normal user agent call processing. For example, when a
user is engaged in a call and another call arrives, such a call
might be rejected with a busy indication. However, some PSTN
operator services require special call processing. In particular,
the Busy line verification (BLV) and Emergency interrupt (EI)
services initiated by an operator from an Operator Services Position
System (OSPS) on the PSTN network have such a need.
In order to inform the SIP user agent that special treatment should
be given to a call, we use a new OSPS header field, which may be set
to a value indicating when a special type of call processing is
requested. We define two values in this header, namely "BLV" for
busy line verification and "EI" for emergency interrupt.
If the user agent decides to honor such a request, the response of
the user agent to an INVITE with either "BLV" or "EI" will not be a
busy indication. When such a request is received, the user agent may
look at the Remote-Party-ID, and decide only to honor the request if
"rpi-type" is "operator" and Remote-Party-ID was authenticated by
the user agent's proxy.
9.1 Syntax
Dcs-OSPS = "Dcs-OSPS" ":" OSPS-Tag
OSPS-Tag = "BLV" | "EI" | token
The OSPS-Tag value of "token" is defined for extensibility, and is
reserved for future use.
9.2 Procedures at an Untrusted User Agent Client (UAC)
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The Dcs-OSPS header MUST NOT be sent in a request from an untrusted
UAC.
9.3 Procedures at a Trusted User Agent Client (UAC)
This header is typically only inserted by a Media-Gateway-Controller
that is controlling a Media Gateway with special MF trunk
connections to a PSTN OSPS system. This trunk group is usually
referred to as a BLV-trunk group, and employs special signaling
procedures that prevent inadvertant use. Calls originating at the
PSTN OSPS system are sent over this trunk group, and result in an
INVITE request with the OSPS header.
This header MAY be sent in an INVITE request, and MUST NOT appear in
any message other than an INVITE request.
OSPS-Tag value "BLV" MUST NOT appear in any INVITE other than an
initial INVITE request establishing a new session.
OSPS-Tag value "EI" MUST NOT appear in any INVITE request other than
a subsequent INVITE within a pre-existing session established with
the OSPS-Tag value of "BLV".
9.4 Procedures at an Untrusted User Agent Server (UAS)
If the UAS receives an INVITE request with an OSPS-Tag, call-leg
identification that matches an existing call, and the existing call
was not established with the OSPS-Tag, it MUST reject the request
with a 409-Conflict error code. If the UAS receives an INVITE
request with an OSPS-Tag value of "EI", with call-leg identification
that does not match an existing call, it MUST reject the request
with a 409-Conflict error code.
If the UAS receives an INVITE that contains an OSPS-Tag value of
"BLV" and is not willing to cooperate in offering this service, it
MUST reject the request with a 403-Forbidden error code. Otherwise,
the UAS MUST verify the Dcs-Remote-Party-ID header contains a rpi-
type token with value "operator." If the call is not from a service-
provider-certified operator, it SHOULD be rejected with a 401-
Unauthorized error code.
The UAS SHOULD NOT reject an INVITE with a BLV OSPS-Tag due to a
busy condition. The UAS MUST NOT respond with a 3xx-Redirect error
code to an INVITE with a BLV OSPS-Tag. The UAS SHOULD NOT alert the
user of the incomming call attempt if the BLV OSPS-Tag is present in
the INVITE.
If an INVITE with OSPS-Tag of "BLV" is accepted (meeting all QoS
pre-conditions, etc.), the UAS MUST send an audio stream on this
conection to the address and port given in the SDP of the INVITE.
The UAS MAY perform a mixing operation between the two ends of an
active call. The UAS MAY send a copy of the local voice stream, and
(if no activity on the local voice stream) send a copy of the
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received voice stream. If the state of the UAS is idle, the UAS
SHOULD send a stream of silence packets to OSPS. If the state of
the UAS is ringing or ringback, the UAS SHOULD send a ringback
stream to OSPS.
If an INVITE with OSPS-Tag of "EI" is accepted, the UAS MUST enable
communication between the UAC and the local user. The UAS MAY put
any existing call on hold, or initiate an ad-hoc conference.
9.5 Procedures at a Trusted User Agent Server (UAS)
The procedures at a trusted UAS are identical to those described in
8.4.
9.6 Procedures at Proxy
There is no special processing of this header at proxies.
10. DCS-BILLING-ID and DCS-BILLING-INFO
In order to deploy a residential telephone service at very large
scale across different domains, it is necessary for trusted elements
owned by different service providers to exchange trusted information
that conveys billing information and expectations about the parties
involved in the call.
There are many billing models used in deriving revenue from
telephony services today. Charging for telephony services is tightly
coupled to the use of network resources. It is outside the scope of
this document to discuss the details of these numerous and varying
methods.
A key motivating principle of the DCS architecture is the need for
network service providers to be able to control and monitor network
resources; revenue may be derived from the usage of these resources
as well as from the delivery of enhanced services such as telephony.
Furthermore, the DCS architecture recognizes the need for
coordination between call signaling and resource management. This
coordination ensures that users are authenticated and authorized
before receiving access to network resources and billable enhanced
services.
Proxies have access to subscriber information and act as policy
decision points and trusted intermediaries along the call signaling
path. Edge routers provide the policy enforcement mechanism and also
capture and report usage information. Edge routers need to be given
billing information that can be logged with Record Keeping or
Billing servers. The proxy, as a central point of coordination
between call signaling and resource management, can provide this
information based on the authenticated identity of the calling and
called parties. Since there is a trust relationship among proxies,
they can be relied upon to exchange trusted billing information
pertaining to the parties involved in a call.
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For these reasons, it is appropriate to consider defining SIP header
extensions to allow proxies to exchange information during call
setup. It is the intent that the extensions would only appear on
trusted network segments, should be inserted upon entering a trusted
network region, and removed before leaving trusted network segments.
Rules for inserting and removing headers exchanged only between
proxies are for further study.
Significant amounts of information is retrieved by an originating
proxy in its handling of a connection setup request from a user
agent. Such information includes location information about the
subscriber (essential for emergency services calls), billing
information, and station information (e.g. coin operated phone). In
addition, while translating the destination number, information such
as the local-number-portability office code is obtained and will be
needed by all other proxies handling this call.
For Usage Accounting records, it is necessary to have an identifier
that can be associated with all the event records produced for the
call. Call-ID cannot be used as such an identifier since it is
selected by the originating user agent, and may not be unique among
all past calls as well as current calls. Further, since this
identifier is to be used by the service provider, it should be
chosen in a manner and in a format that meets the service provider's
needs.
Billing information may not necessarily be unique for each user
(consider the case of calls from an office all billed to the same
account). Billing information may not necessarily be identical for
all calls made by a single user (consider prepaid calls, credit card
calls, collect calls, etc). It is therefore necessary to carry
billing information separate from the calling and called party
identification. Furthermore, some billing models call for split-
charging where multiple entities are billed for portions of the
call.
The addition of two SIP General Header Fields allows for the capture
of billing information and billing identification for the duration
of the call. Alternative techniques such as multi-part attachments
will not coexist with encrypted messages.
It is the intent that the billing extensions would only appear on
trusted network segments, and MAY be inserted by a proxy in INVITE
requests entering a trusted network segment, and removed before
leaving trusted network segments. The Dcs-Billing-ID and Dcs-
Billing-Info header extensions are used only on requests and
responses between proxies. They are never sent to, nor sent by, an
untrusted UAC/UAS.
10.1 Syntax
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The Dcs-Billing-ID and Dcs-Billing-Info headers are defined by the
following BNF.
Dcs-Billing-ID = "Dcs-Billing-ID" ":"
Billing-Correlation-ID "/" FEID
Dcs-Billing-Info = "Dcs-Billing-Info" ":"
[hostport] 1#Acct-Entry
Acct-Entry = Acct-Charge-URI "/"
Acct-Calling-URI "/"
Acct-Called-URI
["/" Acct-Routing-URI
"/" Acct-Loc-Routing-URI]
Acct-Charge-URI = "<" URI ">"
Acct-Calling-URI = "<" URI ">"
Acct-Called-URI = "<" URI ">"
Acct-Routing-URI = "<" URI ">"
Acct-Loc-Routing-URI = "<" URI ">"
Billing-Correlation-ID = 1*hex
FEID = 1*hex
The Dcs-billing-ID extension contains an identifier that can be used
by an event recorder to associate multiple usage records, possibly
from different sources, with a billable account. Dcs-billing-id is
chosen to be globally unique within the system for a window of
several months. This header is only used between proxies.
The Billing-Correlation-ID is specified in other PacketCable
documents as a 16-byte binary structure, containing 4 bytes of NNTP
timestamp, 8 bytes of MAC address of the network element that
generated the ID, and 4 bytes of monotonically increasing sequence
number at that network element. This MUST be encoded in the Dcs-
Billing-ID header as a hex string of up to 32 characters. Leading
zeroes may be suppressed.
The Financial Entity ID (FEID) is specified in other PacketCable
documents as a 4-byte binary structure, containing the financial
identifier for that domain. FEID can be associated with a type of
service and could be assigned to multiple domains by the same
provider. A domain could contain multiple assigned FEIDs. This
MUST be encoded in the Dcs-Billing-ID header as a hex string of up
to 8 characters. Leading zeroes may be suppressed.
The Dcs-billing-info extension identifies a subscriber account
number of the payer, and other information necessary for accurate
billing of the service.
The hostport, if present, specifies a record keeping server for
event messages relating to this call. If not present, the default
record keeping server for each network element is sent the event
messages.
Acct-data contains the information needed by the Gate Controller to
give to the CMTS for generation of event message records. Acct-
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Charge-URI, Acct-Calling-URI, Acct-Called-URI, Acct-Routing-URI, and
Acct-Location-Routing-URI are each defined as URLs; they should all
contain tel: URLs with E.164 formatted addresses.
10.2 Procedures at an Untrusted User Agent Client (UAC)
This header is never sent to an untrusted UAC, and is never sent by
an untrusted UAC.
10.3 Procedures at a Trusted User Agent Client (UAC)
The UAC MUST generate the Billing-Correlation-ID for the call, and
insert the Dcs-Billing-ID header into the initial INVITE message
sent to the terminating proxy.
If the response to the initial INVITE is a 3xx-Redirect, the UAC
generates a new initial INVITE request to the destination specified
in the Contact: header, as per standard SIP. If a UAC receives a
3xx-Redirect response to an initial INVITE, the INVITE generated by
the UAC MUST contain the Dcs-Billing-Info headers from the 3xx-
Redirect response.
An originating proxy that includes a Refer-to header in a REFER
request MUST include a Dcs-Billing-Info header in the Refer-to's
URL. This Dcs-Billing-Info header MUST include the accounting
information of the initiator.
A UAC that sends a mid-call REFER request including a Refer-to
header MUST include a Dcs-Billing-ID header and one or more Dcs-
Billing-Info headers attached to the Refer-to. The Dcs-Billing-Info
headers MUST include the complete set of Dcs-Billing-Info headers
associated with the current call, and MUST include one additional
Dcs-Billing-Info header (for the segment from the initiator) with
accounting information of the initiator.
10.4 Procedures at an Untrusted User Agent Server (UAS)
This header is never sent to an untrusted UAS, and is never sent by
an untrusted UAS.
10.5 Procedures at a Trusted User Agent Server (UAS)
The UAS MAY include a Dcs-Billing-Info header in the first non-100
response to an initial INVITE message if it wishes to override the
billing information that was present in the INVITE (e.g. for a toll-
free call). The decision to do this and the contents of the
resulting Dcs-Billing-Info header MUST be determined by service
provider policy provisioned in the UAS.
The UAS MUST add Dcs-Billing-Info headers to a 3xx-redirect response
to an initial INVITE. All Dcs-Billing-Info headers present in the
initial INVITE MUST be copied to the 3xx-redirect response. In
addition, the UAS MUST add an additional Dcs-Billing-Info header,
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SIP Proxy-to-Proxy Extensions February 2002
for the segment from the destination to the forwarded-to
destination, giving the accounting information for the call
forwarder.
10.6 Procedures at Proxy
Two sets of proxy procedures are defined: (1) the procedures at an
originating proxy, and (2) the procedures at a terminating proxy.
The originating proxy is a proxy that received the INVITE request
from a non-trusted endpoint.
The terminating proxy is a proxy that sends the INVITE request to a
non-trusted endpoint.
For purposes of mid-call changes, such as call transfers, the proxy
that receives the request from a non-trusted endpoint is considered
the initiating proxy; the proxy that sends the request to a non-
trusted endpoint is considered the recipient proxy. Procedures for
the initiating proxy are included below with those for originating
proxies, while procedures for the recipient proxy are included with
those for terminating proxies.
A proxy that both receives the INVITE request from an untrusted
endpoint, and sends the INVITE request to a non-trusted endpoint,
does not generate Dcs-Billing-ID nor Dcs-Billing-Info headers.
A proxy that is neither an originating proxy nor a terminating proxy
has no function in manipulating existing calls.
10.6.1 Procedures at Originating Proxy
The originating proxy MUST generate the Billing-Correlation-ID for
the call, and insert the Dcs-Billing-ID header into the initial
INVITE message sent to the terminating proxy.
If the Request-URI contains a private-param, and the decoded
username contains billing information, the originating proxy MUST
generate a Dcs-Billing-Info header with that decrypted information.
Otherwise, the originating proxy MUST determine the accounting
information for the call originator, and insert a Dcs-Billing-Info
header including that information.
If the response to the initial INVITE is a 3xx-Redirect, received
prior to a 18x-Ringing, the originating proxy generates a new
initial INVITE request to the destination specified in the Contact:
header, as per standard SIP. If an originating proxy receives a
3xx-Redirect response to an initial INVITE prior to a 18x-Ringing
response, the INVITE generated by the proxy MUST contain the Dcs-
Billing-Info headers from the 3xx-Redirect response.
If the response to the initial INVITE is a 3xx-Redirect, received
after a 18x-Ringing, the originating proxy generates a private URL
and places it in the Contact header of a 3xx-Redirect response sent
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SIP Proxy-to-Proxy Extensions February 2002
to the originating endpoint. This private URL MUST contain the
sequence of Dcs-Billing-Info values, which indicate the complex
charging arrangement for the new call, and an expiration time very
shortly in the future, to limit the ability of the originator to re-
use this private-param for multiple calls.
An originating proxy that includes a Refer-to header in a REFER
request MUST include a Dcs-Billing-Info header in the Refer-to's
URL. This Dcs-Billing-Info header MUST include the accounting
information of the initiator.
An initiating proxy that sends a REFER request including a Refer-to
header MUST include a Dcs-Billing-ID header and one or more Dcs-
Billing-Info headers in the Refer-to's URL. The Dcs-Billing-Info
headers MUST include the complete set of Dcs-Billing-Info headers
associated with the current call, and MUST include one additional
Dcs-Billing-Info header (for the segment from the initiator) with
accounting information of the initiator.
10.6.2 Procedures at Terminating Proxy
The terminating proxy MUST NOT send the Dcs-Billing-ID nor the Dcs-
Billing-Info headers to a non-trusted destination.
The terminating proxy MAY include a Dcs-Billing-Info header in the
first non-100 response to an initial INVITE message if it wishes to
override the billing information that was present in the INVITE
(e.g. for a toll-free call). The decision to do this and the
contents of the resulting Dcs-Billing-Info header MUST be determined
by service provider policy provisioned in the terminating proxy.
The terminating proxy MUST add Dcs-Billing-Info headers to a 3xx-
redirect response to an initial INVITE. All Dcs-Billing-Info
headers present in the initial INVITE MUST be copied to the 3xx-
redirect response. In addition, the terminating proxy MUST add an
additional Dcs-Billing-Info header, for the segment from the
destination to the forwarded-to destination, giving the accounting
information for the call forwarder.
A proxy receiving a mid-call REFER request that includes a Refer-to
header generates a private URL and places it in the Refer-to header
sent to the endpoint. This private URL MUST contain the value of
Dcs-Billing-ID, the sequence of Dcs-Billing-Info values, which
indicate the complex charging arrangement for the new call, and an
expiration time very shortly in the future, to limit the ability of
the endpoint to re-use this private-param for multiple calls.
11. DCS-LAES and DCS-REDIRECT
The Dcs-Laes extension contains the information needed to support
Lawfully Authorized Electronic Surveillance. This header contains
the address and port of an Electronic Surveillance Delivery Function
for delivery of a duplicate stream of event messages related to this
call. The header may also contain an additional address and port
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SIP Proxy-to-Proxy Extensions February 2002
for delivery of call content. Security key information is included
to enable pairs of Delivery Functions to securely exchange
surveillance information. This header is only used between proxies.
The Dcs-Redirect extension contains call identifying information
needed to support the requirements of Lawfully Authorized Electronic
Surveillance of redirected calls. This header is only used between
proxies.
11.1 Syntax
The format of the Dcs-Laes header is given by the following BNF.
Dcs-LAES = "Dcs-LAES" ":" Laes-sig ["," Laes-content]
";" Laes-key
Laes-sig = hostport
Laes-content = hostport
Laes-key = token
Dcs-Redirect = "Dcs-Redirect" ":" Called-id Redirector
Num-redir
Called-id = "<" SIP-URL ">"
Redirector = "<" SIP-URL ">"
Num-redir = 1*DIGIT
The values of Laes-sig and Laes-content are addresses of the
Electronic Surveillance Delivery Function, and used as the
destination address for call-identifying information and call-
content, respectively.
Laes-key is a string generated by the proxy that is used by the
Delivery Function to securely transfer information between them.
11.2 Procedures at an Untrusted User Agent Client (UAC)
This header is never sent to an untrusted UAC, and is never sent by
an untrusted UAC.
11.3 Procedures at a Trusted User Agent Client (UAC)
The UAC checks for an outstanding lawfully authorized surveillance
order for the originating subscriber, and, if present, includes this
information in the Authorization for Quality of Service or signals
this information to the device performing the intercept (e.g. a
Media Gateway).
If the Dcs-LAES header is present in the 183-Session-Progress
response (indicating surveillance is required on the terminating
subscriber, but that the terminating equipment is unable to perform
that function), the UAC MUST include this information in the
Authorization for Quality of Service, or MUST signal this
information to the device performing the intercept (e.g. a Media
Gateway).
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If a 3xx-Redirect response is received to the initial INVITE
request, and if a Dcs-LAES header is present in the 3xx response,
the UAC MUST include that header unchanged in the reissued INVITE.
The UAC MUST also include a Dcs-Redirect header containing the
original dialed number, the new destination number, and the number
of redirections that have occurred.
A UAC that includes a Refer-to header in a REFER request, when the
originating subscriber has an outstanding lawfully authorized
surveillance order, MUST include a Dcs-Laes header attached to the
Refer-to. The Dcs-LAES header MUST include the address and port of
the local Electronic Surveillance Delivery Function for a copy of
the call's event messages, MUST include the address and port of the
local Electronic Surveillance Delivery Function for the copy of call
content if call content is to be intercepted, and MUST include a
random string for use as a security key between the Delivery
Functions.
The trusted UAC MUST NOT send the Dcs-Laes and Dcs-Redirect headers
to an untrusted entity.
11.4 Procedures at an Untrusted User Agent Server (UAS)
This header is never sent to an untrusted UAS, and is never sent by
an untrusted UAS.
11.5 Procedures at a Trusted User Agent Server (UAS)
The UAS checks for an outstanding lawfully authorized surveillance
order for the terminating subscriber. If present, the UAS includes
this information in the authorization for Quality of Service.
If the terminating equipment is unable to perform the required
surveillance (e.g. if the destination is a voicemail server), the
UAS MUST include a Dcs-LAES header in the 183-Session-Progress
response requesting the originating proxy to perform the
surveillance. The Dcs-LAES header MUST include the address and port
of the local Electronic Surveillance Delivery Function for a copy of
the call's event messages, MUST include the address and port of the
local Electronic Surveillance Delivery Function for the copy of call
content if call content is to be intercepted, and MUST include a
random string for use as a security key between the Delivery
Functions.
If the response to the initial INVITE request is a 3xx-Redirect
response, and there is an outstanding lawfully authorized
surveillance order for the terminating subscriber, the UAS MUST
include a Dcs-Laes header in the 3xx-Redirect response, with
contents as described above.
The trusted UAS MUST NOT send the Dcs-Laes and Dcs-Redirect headers
to an untrusted entity.
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11.6 Procedures at Proxy
Two sets of proxy procedures are defined: (1) the procedures at an
originating proxy, and (2) the procedures at a terminating proxy.
The originating proxy is a proxy that received the INVITE request
from a non-trusted endpoint.
The terminating proxy is a proxy that sends the INVITE request to a
non-trusted endpoint.
For purposes of mid-call changes, such as call transfers, the proxy
that receives the request from a non-trusted endpoint is considered
the initiating proxy; the proxy that sends the request to a non-
trusted endpoint is considered the recipient proxy. Procedures for
the initiating proxy are included below with those for originating
proxies, while procedures for the recipient proxy are included with
those for terminating proxies.
A proxy that both receives the INVITE request from an untrusted
endpoint, and sends the INVITE request to a non-trusted endpoint,
does not generate Dcs-Laes nor Dcs-Redirect headers.
A proxy that is neither an originating proxy nor a terminating proxy
has no function in manipulating existing calls.
11.6.1 Procedures at Originating Proxy
The originating proxy checks for an outstanding lawfully authorized
surveillance order for the originating subscriber, and, if present,
includes this information in the Authorization for Quality of
Service or signals this information to the device performing the
intercept (e.g. a Media Gateway).
If the Dcs-LAES header is present in the 183-Session-Progress
response (indicating surveillance is required on the terminating
subscriber, but that the terminating equipment is unable to perform
that function), the originating proxy MUST include this information
in the Authorization for Quality of Service, or MUST signal this
information to the device performing the intercept (e.g. a Media
Gateway).
If the Request-URI in an initial INVITE request contains the
private-param user parameter, the originating proxy MUST decrypt the
username information to find the real destination for the call, and
other special processing information. If electronic surveillance
information is contained in the decrypted username, the originating
proxy MUST generate a Dcs-LAES header with the surveillance
information.
If a 3xx-Redirect response is received to the initial INVITE request
prior to a 18x-Ringing, and if a Dcs-LAES header is present in the
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SIP Proxy-to-Proxy Extensions February 2002
3xx response, the originating proxy MUST include that header
unchanged in the reissued INVITE. The originating proxy MUST also
include a Dcs-Redirect header containing the original dialed number,
the new destination number, and the number of redirections that have
occurred.
If a 3xx-Redirect response is received to the initial INVITE request
after a 18x-Ringing, the originating proxy generates a private URL
and places it in the Contact header of a 3xx-Redirect response sent
to the originating endpoint. If a Dcs-Laes header is present in the
3xx response, this private URL MUST contain (1) the electronic
surveillance information from the 3xx-Redirect response, (2) the
original destination number, (3) the identity of the redirecting
party, and (4) the number of redirections of this call.
An originating proxy that includes a Refer-to header in a REFER
request, when the originating subscriber has an outstanding lawfully
authorized surveillance order, MUST include a Dcs-Laes header in the
Refer-to's URL. The Dcs-LAES header MUST include the address and
port of the local Electronic Surveillance Delivery Function for a
copy of the call's event messages, MUST include the address and port
of the local Electronic Surveillance Delivery Function for the copy
of call content if call content is to be intercepted, and MUST
include a random string for use as a security key between the
Delivery Functions.
An initiating proxy that sends a mid-call REFER request including a
Refer-to header, when the initiating subscriber has an outstanding
lawfully authorized surveillance order, MUST include a Dcs-Laes
header in the Refer-to's URL. The Dcs-Laes header MUST include the
information listed above.
The originating proxy MUST NOT send the Dcs-Laes and Dcs-Redirect
headers to an untrusted entity.
11.6.2 Procedures at Terminating Proxy
The terminating proxy checks for an outstanding lawfully authorized
surveillance order for the terminating subscriber. If present, the
terminating proxy includes this information in the authorization for
Quality of Service.
The terminating proxy MUST NOT send the Dcs-Laes and Dcs-Redirect
headers to an untrusted entity.
If the terminating equipment is unable to perform the required
surveillance (e.g. if the destination is a voicemail server), the
terminating proxy MUST include a Dcs-LAES header in the 183-Session-
Progress response requesting the originating proxy to perform the
surveillance. The Dcs-LAES header MUST include the address and port
of the local Electronic Surveillance Delivery Function for a copy of
the call's event messages, MUST include the address and port of the
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local Electronic Surveillance Delivery Function for the copy of call
content if call content is to be intercepted, and MUST include a
random string for use as a security key between the Delivery
Functions.
If the response to the initial INVITE request is a 3xx-Redirect
response, and there is an outstanding lawfully authorized
surveillance order for the terminating subscriber, the terminating
proxy MUST include a Dcs-Laes header in the 3xx-Redirect response,
with contents as described above.
A proxy receiving a mid-call REFER request that includes a Refer-to
header with a Dcs-laes header attached MUST generate a private URL
and place it in the Refer-to header sent to the endpoint. This
private URL MUST contain the Dcs-Laes information from the attached
header.
12. Security Considerations
Billing information is often considered sensitive and private
information to the customers. It is therefore necessary that the
Proxies take precautions to protect this information from
eavesdropping and interception. Use of IPSec between Proxies is
recommended.
13. 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.
14. References
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 DCS Group, "Architectural Considerations for Providing Carrier
Class Telephony Services Utilizing SIP-based Distributed Call
Control Mechanisms", draft-dcsgroup-sip-arch-04.txt, February
2001.
15. Acknowledgements
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SIP Proxy-to-Proxy Extensions February 2002
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.
16. Author's Addresses
Bill Marshall
AT&T
Florham Park, NJ 07932
Email: wtm@research.att.com
K. K. Ramakrishnan
TeraOptic Networks
Summit, NJ 07901
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
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
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SIP Proxy-to-Proxy Extensions February 2002
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
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
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SIP Proxy-to-Proxy Extensions 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
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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
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followed, or as required to translate it into languages other than
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INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
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This memo is filed as <draft-dcsgroup-sip-proxy-proxy-06.txt>, and
expires August 31, 2002.
DCS Group Category Informational - Expiration 8/31/02 26
