Internet DRAFT - draft-foster-mgcp-redirect
draft-foster-mgcp-redirect
Internet Engineering Task Force B. Foster
Internet Draft F. Andreasen
Document: <draft-foster-mgcp-redirect-05.txt> Cisco Systems
Category: Informational July 2003
Media Gateway Control Protocol (MGCP) Redirect and Reset Package
Status of this Document
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026
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.
Abstract
The base Media Gateway Control Protocol (MGCP) specification (RFC
3435) allows endpoints to be re-directed one endpoint at a time.
This document provides extensions in the form of a new MGCP package
that provides mechanisms for redirecting and resetting a group of
endpoints. It also includes the ability to more accurately re-direct
endpoints by allowing a list of Call Agents to be specified in a
preferred order.
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 [1].
B. Foster, F. Andreasen Informational [Page 1]
MGCP Redirect and Reset Package July 2003
Table of Contents
1. Introduction......................................................2
2.0. Redirect and Reset Package......................................3
2.1. NotifiedEntityList Extension Parameter.........................3
2.2. Endpoint Specifier.............................................4
2.2.1. EndpointList and EndpointMap Extension Parameters..........4
2.2.2. Application to Out-of-Service Endpoints....................5
2.3. Redirect.......................................................6
2.4. Reset Extension Parameter......................................7
2.5. Return Codes...................................................7
3.0. IANA Considerations.............................................8
4.0. Security Considerations.........................................8
5.0. Normative References............................................8
Authors' Addresses....................................................8
Intellectual Property Statement.......................................8
Full Copyright Statement..............................................9
Acknowledgement.......................................................9
1. Introduction
The base Media Gateway Control Protocol (MGCP) specification [2]
allows a Call Agent to specify a new NotifiedEntity parameter in
order to re-direct one or more endpoints to a new Call Agent. This
must be done in a NotificationRequest or a connection handling
command. However, because these commands affect endpoint or
connection state, such a request cannot typically be sent to a group
of endpoints with a single command. This means that in a case where
a new Call Agent takes over for a failed one, the new Call Agent must
re-direct endpoints one at a time. If there is a large number of
endpoints (e.g., within a large trunking gateway) this could take a
considerable amount of time.
This document defines a new redirect and reset package for MGCP that
allows the Call Agent to re-direct a group of endpoints without
affecting endpoint or connection state.
Also included is a new NotifiedEntityList parameter, which is similar
to the NotifiedEntity parameter but allows for multiple domain names
to be provided. This allows the Call Agent to more accurately direct
endpoints to a preferred ordered list of alternate Call Agents.
A third capability contained within this package is the ability to
efficiently reset and re-initialize one or more groups of endpoints.
Such a capability is useful during Call Agent failover situations.
B. Foster, F. Andreasen Informational [Page 2]
MGCP Redirect and Reset Package July 2003
2.0. Redirect and Reset Package
Package Name: RED
Version: 0
The purpose of this package is to:
* Define a new NotifiedEntityList extension parameter. This works
the same as the NotifiedEntity parameter in [2] but allows more
than one domain name to be specified.
* Allow a Call Agent to pass a new NotifiedEntity or
NotifiedEntityList to a collection of endpoints specified by an
"all of" wildcard. This is useful in the case where a new Call
Agent takes over from a previous one and wants to re-direct
endpoint(s) to send "Notifies" etc. to it from now on.
* Allow a Call Agent to request one or more groups of endpoints to
do a reset, which can be useful following certain types of
failures.
2.1. NotifiedEntityList Extension Parameter
The NotifiedEntityList parameter is encoded as "NL" and is followed
by a colon and a comma-separated list of NotifiedEntity values as
defined in the MGCP specification [2], e.g.:
RED/NL: ca1@myca.whatever.net, ca2@mybackupca.whatever.net
The NotifiedEntityList works in a similar way to the NotifiedEntity
parameter, except that it allows multiple domain names to be listed.
The NotifiedEntityList thus specifies a new "notified entity" for the
endpoint.
The NotifiedEntityList parameter is optional in any command or
response where the NotifiedEntity parameter is allowed. Following a
restart, the NotifiedEntityList is initially empty, unless
provisioned otherwise. In subsequent commands, it retains its
current value until explicitly changed. If both a NotifiedEntity
parameter and a non-empty NotifiedEntityList parameter have been set
(not necessarily at the same time), the NotifiedEntity parameter
value will be viewed as implicitly added to the beginning of the
NotifiedEntityList parameter. The NotifiedEntity parameter thus
always defines the first domain name to contact, unless it has
explicitly been set to empty. In that case, the NotifiedEntityList
defines the "notified entity". If the NotifiedEntityList is also
empty, then the normal MGCP handling of having an empty "notified
entity" applies. We will refer to the list of domain names that
result from the above rules as the "notified entity list".
When the "notified entity list" is non-empty, transmission is first
attempted with the first domain name in the list as in the normal
MGCP retransmission procedures described in [2]. Each of the IP-
addresses for this domain name MUST first be tried as specified in
[2], and if this is unsuccessful, each of the IP-addresses for the
second domain name MUST then be attempted, etc. following the normal
B. Foster, F. Andreasen Informational [Page 3]
MGCP Redirect and Reset Package July 2003
MGCP retransmission procedures, with "N" (the number of
retransmissions) set to zero for each domain name (see Section 4.3 in
[2]). Whenever retransmission to a new domain name is initiated, the
default retransmission timer value (RTO) etc. SHOULD be used - the
estimator (T-DELAY) and measurements (AAD and ADEV) used for the
transmission to the previous domain name are considered obsolete.
Note however, that the maximum transaction lifetime considerations
apply as usual, and hence retransmission to any of the IP-addresses
for any of the domain names MUST NOT occur more than T-Max seconds
after the initial sending of the command, irrespective of where it
was sent. The Max1 DNS query MAY be performed for each of the domain
names, or it MAY simply be performed for the first domain name. The
Max2 DNS query however MUST NOT be performed for any but the last
domain name. Also note, that only the last IP-address for the last
domain name can reach Max2 retransmissions, and hence retransmission
to all other IP-addresses MUST end after Max1 retransmissions.
The current value of the NotifiedEntityList parameter can be audited
via AuditEndpoint; the value of the NotifiedEntity parameter will not
be included here and hence must be audited separately. Support for
the NotifiedEntityList in AuditConnection is permissible, but it is
neither required nor recommended.
2.2. Endpoint Specifier
2.2.1. EndpointList and EndpointMap Extension Parameters
A simple "all-of" wildcard as defined in [2] may not be sufficient to
accurately specify endpoints of interest. An example of this is a
case where a Call Agent fails over, resulting in a state mismatch for
endpoints involved with transient calls. In order to re-synchronize,
one Call Agent procedure involves using the reset extension parameter
described in section 2.4 of this document to ensure that idle
endpoints are in fact idle. However, these endpoints may be randomly
distributed across the available endpoints in a large trunk gateway.
In order to satisfy this requirement, the RED package introduces some
new parameters that MAY be used to specify the endpoints of interest
for the EndpointConfiguration Command. These are the EndpointList
and the EndpointMap extension parameters. These parameters MUST only
be used when specifying a virtual endpoint corresponding to the
gateway as the LocalEndpointName i.e.:
EPCF 1200 MG@gw1.whatever.net MGCP 1.0
where "MG" is the virtual endpoint name associated with the gateway.
The EndPointList parameters is a list of the endpoint names which can
include one or more lines in the following format:
"RED/EL:" 0*WSP RangedLocalName 0*("," 0*WSP RangedLocalName)
B. Foster, F. Andreasen Informational [Page 4]
MGCP Redirect and Reset Package July 2003
where RangedLocalName is a LocalEndpointName that may include the
ranged wildcard notation described in Appendix E (section E.5) of
[2], i.e.:
RangeWildcard = "*" / "[" NumericalRange *("," NumericalRange)"]"
NumericalRange = 1*(DIGIT) [ "-" 1*(DIGIT) ]
Example:
RED/EL: ds/ds1-1/[1-24], ds/ds1-2/[1-24], ds/ds1-3/[1-24]
Including an EndpointMap parameter with the following format can
further specify the endpoints:
"RED/MP:" 0*WSP TrueOrFalse 0*(TrueOrFalse)
TrueOrFalse = "T" / "F"
where "T" indicates that the command should be applied to this
endpoint and "F" indicates that it should not. This parameter can be
used in conjunction with the reset extension parameter described in
section 2.4 of this document to force arbitrarily distributed
endpoints to an idle state.
If the EndpointMap parameter is used it MUST be immediately preceded
(i.e. on the previous line) by an EndPointList parameter to specify
the endpoints that the EndpointMap is referring to. Several
EndpointList and EndpointMap parameter lines MAY be provided. It is
considered to be an error if the EndpointMap parameters extend beyond
the endpoints specified in the preceding EndPointList parameter. In
that case, return code 800 MUST be used (see section 2.5).
The EndpointList and EndpointMap parameters MUST only be used with
the EndpointConfiguration command. The EndpointList parameter MAY be
provided without an EndpointMap parameter. However, as indicated
earlier, an EndpointMap parameter MUST be immediately preceded by an
EndpointList parameter. Neither of these parameters is auditable.
For an example of EndpointMap parameter usage, refer to section 2.4.
2.2.2. Application to Out-of-Service Endpoints
Note that the EndpointConfiguration command is normally only valid
for in-service endpoints. If an EndpointConfiguration request is
sent to a wild-carded LocalEndpointName [2] and any of the endpoints
specified are out-of-service, the command will fail with return code
501 (endpoint not ready).
However, as long as the gateway is in-service and able to respond to
MGCP commands, the gateway can apply the endpoint configuration
command to endpoints specified by the EndpointList and/or EndpointMap
parameters (regardless of whether those endpoints are in-service or
not). The endpoint configuration information of course will not be
maintained over gateway restarts (i.e. the Call Agent would have to
B. Foster, F. Andreasen Informational [Page 5]
MGCP Redirect and Reset Package July 2003
re-apply the endpoint configuration after it receives an RSIP with
restart method "restart").
EndpointList and/or EndpointMap parameters MUST only be used with a
virtual endpoint name corresponding to the gateway (as indicated
above). If used with any other endpoint name (whether wild-carded or
not), then error code 801 (section 2.5) MUST be returned.
2.3. Redirect
A new extension parameter for use with the EndpointConfiguration
command is defined. A new NotifiedEntity value can be included with
a "RED/N" parameter as follows:
EPCF 1200 *@gw1.whatever.net MGCP 1.0
RED/N: ca1@ca1234.whatever.net
This changes the "notified entity" for the endpoint(s) to the value
specified. If the "all of" wildcard convention is used, the
NotifiedEntity value replaces all of the existing "notified entities"
for those endpoints. If NotifiedEntity is omitted in a subsequent
EndpointConfiguration command, the "notified entity" remains
unchanged.
In the case where the "notified entity" is a domain name that
resolves to multiple IP addresses, one of the resolved addresses MUST
be selected. If one of those IP addresses is the IP address of the
Call Agent sending the request, that IP address SHOULD be selected
first.
The NotifiedEntityList parameter can also be specified in an endpoint
configuration command, e.g.:
EPCF 1200 *@gw1.whatever.net MGCP 1.0
RED/NL: ca1@myca.whatever.net, ca2@mybackupca.whatever.net
As indicated in section 2.2, it can also apply this to the gateway
virtual endpoint e.g.:
EPCF 1200 MG@gw1.whatever.net MGCP 1.0
RED/EL: *
RED/NL: ca1@myca.whatever.net, ca2@mybackupca.whatever.net
As indicated in section 2.1, the NotifiedEntityList ("RED/NL")
parameter MAY be used with any command for which a NotifiedEntity
parameter is allowed. However, the "RED/N" parameter SHOULD only be
used with the endpoint configuration command.
The "RED/N" parameter does not have a default value, and the auditing
behavior for auditing the "NotifiedEntity" is unchanged from that
specified in [2], regardless of how the "NotifiedEntity" was set
(i.e. there is no specific audit associated with the "RED/N"
parameter and hence the "RED/N" parameter cannot be audited).
B. Foster, F. Andreasen Informational [Page 6]
MGCP Redirect and Reset Package July 2003
2.4. Reset Extension Parameter
Another EndpointConfiguration parameter ("RED/R"), allows the Call
Agent to reset one or more endpoints. The ABNF syntax for the
parameter line is as follows:
"RED/R:" 0*WSP "reset"
This has the effect of re-setting and re-initializing the specified
endpoints (i.e. any connections on the endpoint will be deleted, and
the endpoint will be returned to its clean default state without any
active signals, etc.).
Example:
EPCF 1200 mg@gw1.whatever.net MGCP 1.0
RED/EL: ds/e1-3/[1-30]
RED/MP: TFTTTTTFFFTTTTTFFFFTFFTTFTTTFF
RED/EL: ds/e1-5/[1-30]
RED/MP: TFFFFFTFFFTTFTTFFFFTFFFTFTTTTT
RED/R: reset
In this case, the particular endpoints specified by "T" by the
EndpointMap parameter in the E1 spans ds/e1-3 and ds/e1-5 are reset.
The "RED/R" parameter MUST NOT be used with any command other than
the endpoint configuration parameter. There is no default value for
the parameter and hence when omitted, it does not affect operation.
There is no specific audit behavior associated with this parameter,
i.e. it cannot be audited.
2.5. Return Codes
The following package specific return codes are defined for the "RED"
package:
Code Text Explanation
800 EndpointMap Either the EndpointMap parameters
Out of Range are outside the range specified by
the EndpointList parameter or the
EndpointList Parameter was not
included when an EndpointMap
parameter was included.
801 Incorrect Usage Incorrect usage of parameters such
Of Parameters as EndpointList parameter used
where the endpoint name was not
the virtual endpoint name
corresponding to the gateway.
B. Foster, F. Andreasen Informational [Page 7]
MGCP Redirect and Reset Package July 2003
3.0. IANA Considerations
The MGCP package title "Redirect and Reset" with the name "RED" and
version number 0 should be registered with IANA as indicated in
Appendix C.1 in [2].
4.0. Security Considerations
Section 5 of the base MGCP specification [2] discusses security
requirements for the base protocol, which apply equally to the
package defined in this document. Use of a security Protocol such as
IPsec (RFC 2401, RFC 2406) that provides per message authentication
and integrity services is required in order to ensure that requests
and responses are obtained from authenticated sources and that
messages have not been modified. Without such services, gateways and
Call Agents are open to attacks.
For example, without such security services an attacker could
masquerade as a Call Agent and initiate a denial of service attack by
resetting endpoints that were involved in valid calls. Another attack
using the package described in this document could involve re-
directing endpoints to itself so that it now acts as the Call Agent
for those endpoints.
5.0. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] F. Andreasen, B. Foster "Media Gateway Control Protocol (MGCP)
Version 1.0", RFC 3435, January 2003
Authors' Addresses
Flemming Andreasen
Cisco Systems
499 Thornall Street, 8th Floor
Edison, NJ 08837
EMail: fandreas@cisco.com
Bill Foster
Cisco Systems
EMail: bfoster@cisco.com
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
B. Foster, F. Andreasen Informational [Page 8]
MGCP Redirect and Reset Package July 2003
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
Full Copyright Statement
Copyright (C) The Internet Society (2003). 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.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
B. Foster, F. Andreasen Informational [Page 9]
