Network Working Group K. Drage
Internet-Draft Alcatel-Lucent
Intended status: Informational October 20, 2008
Expires: April 23, 2009
A Session Initiation Protocol (SIP) Extension for the Identification of
Services
draft-drage-sipping-service-identification-02
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Abstract
This document describes private extensions to the Session Initiation
Protocol (SIP) that enable a network of trusted SIP servers to assert
the service of authenticated users. The use of these extensions is
only applicable inside an administrative domain with previously
agreed-upon policies for generation, transport and usage of such
information. This document does NOT offer a general service
identification model suitable for use between different trust
domains, or use in the Internet at large.
The document also defines a URN to identify both services and UA
applications. This URN can be used to identify services within the
SIP header fields defined in this document, and also within the
framework defined for caller preferences and callee capabilities in
to identify usage of both services and applications between end UAs.
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1. Introduction
This document describes private extensions to the Session Initiation
Protocol (SIP) that enable a network of trusted SIP servers to assert
the service possibly subject to the user being entitled to that
service. The use of these extensions is only applicable inside an
administrative domain with previously agreed-upon policies for
generation, transport and usage of such information. This document
does NOT offer a general service model suitable for use between
different trust domains, or use in the Internet at large.
The concept of "service" within SIP has no hard and fast rules.
draft-ietf-sipping-service-identification
[I-D.ietf-sipping-service-identification] provides general guidance
on what constitutes a service within SIP and what does not.
This document also makes use of the terms "derived service
identification" and "declarative service identification" as defined
in draft-ietf-sipping-service-identification
[I-D.ietf-sipping-service-identification].
During a session setup proxies may need to understand what service
the request is related to in order to know what application server to
contact or other service logic to invoke. The SIP INVITE request
contains all of the information necessary to determine the service.
However, the calculation of the service may be computational and
database intensive. For example, a given trust domain's definition
of a service might include request authorization. Moreover the
analysis may require examination of the SDP.
For example, an INVITE request with video SDP directed to a video-on-
demand Request-URI could be marked as an IPTV session. An INVITE
request with push-to-talk over cellular (PoC) routes could be marked
as a PoC session. An INVITE request with a Require header field
containing an option tag of "foogame" could be marked as a foogame
session.
NOTE: If the information contained within the SIP INVITE request is
not sufficient to uniquely identify a service, the remedy is to
extend the SIP signalling to capture the missing element.
draft-ietf-sipping-service-identification
[I-D.ietf-sipping-service-identification] provides further
explanation.
By providing a mechanism to compute and store the results of the
domain specific service calculation, i.e. the derived service
identification, this optimization allows a single trusted proxy to
perform an analysis of the request and authorize the requestor's
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permission to request such a service. The proxy may then include a
service identifier that relieves other trusted proxies and trusted
UAs from performing further duplicate analysis of the request for
their service identification purposes. In addition, this extension
allows user agent clients outside the trust domain to provide a hint
of the requested service.
This extension does not provide for the dialog or transaction to be
rejected if the service is not supported end-to-end. SIP provides
other mechanisms, such as the option-tag and use of the Require and
Proxy-Require header fields, where such functionality is required.
No explicitly signalled service identification exists and the session
proceeds for each nodes definition of the service in use, on the
basis of information contained in SDP and in other SIP header fields.
This mechanism is specifically a mechanism to manage the information
needs of intermediate routeing devices between the calling user and
the user represented by the Request-URI. In support of this
mechanism, a URN is defined to identify the services. This URN has
wider applicability to additionally identify services and terminal
applications. Between end users, caller preferences and callee
capabilities as specified in RFC 3840 [RFC3840] and RFC 3841
[RFC3841] provide an appropriate mechanism for indicating such
service and application identification. These mechanisms have been
extended by draft-rosenberg-sip-app-media-tag
[I-D.rosenberg-sip-app-media-tag] to provide further capabilities in
this area.
The mechanism proposed in this document relies on a new header field
called 'P-Asserted-Service' that contains a URN. This is supported
by a further new header field called 'P-Preferred-Service' that also
contains a URN, and which allows the UA to express a preferences to
the decisions made on service within the trust domain.
P-Asserted-Service: urn-xxx:exampletelephony.version1
A proxy server which handles a request can, after authenticating the
originating user in some way (for example: Digest authentication), to
ensure that the user is entitled to that service, insert such a
P-Asserted-Service header field into the request and forward it to
other trusted proxies. A proxy that is about to forward a request to
a proxy server or UA that it does not trust removes all the
P-Asserted-Service header field values.
This document labels services by means of an informal URN. This
provides a hierarchical structure for defining services and
subservices, and provides an address that can be resolvable for
various purposes outside the scope of this document, e.g. to obtain
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information about the service so described.
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2. Applicability Statement
This document describes private extensions to SIP (see RFC 3261
[RFC3261]) that enable a network of trusted SIP servers to assert the
service of end users or end systems. The use of these extensions is
only applicable inside a 'Trust Domain' as defined in Short term
requirements for Network Asserted Identity (see RFC 3324 [RFC3324]).
Nodes in such a Trust Domain are explicitly trusted by its users and
end-systems to publicly assert the service of each party, and that
they have common and agreed upon definitions of services and
homogeneous service offerings. The means by which the network
determines the service to assert is outside the scope of this
document (though it commonly entails some form of authentication).
The mechanism for defining a trust domain is to provide a certain set
of specifications known as 'Spec(T)', and they specify compliance to
that set of specifications. Spec(T) MUST specify behavior as
documented in RFC 3324 [RFC3324].
This document does NOT offer a general service model suitable for
inter-domain use or use in the Internet at large. Its assumptions
about the trust relationship between the user and the network may not
apply in many applications. For example, these extensions do not
accommodate a model whereby end users can independently assert their
service by use of the extensions defined here. End users assert
their service by including the SIP and SDP parameters that correspond
to the service they require. Furthermore, since the asserted
services are not cryptographically certified, they are subject to
forgery, replay, and falsification in any architecture that does not
meet the requirements of RFC 3324 [RFC3324].
The asserted services also lack an indication of who specifically is
asserting the service, and so it must be assumed that a member of the
Trust Domain is asserting the service. Therefore, the information is
only meaningful when securely received from a node known to be a
member of the Trust Domain.
Despite these limitations, there are sufficiently useful specialized
deployments that meet the assumptions described above, and can accept
the limitations that result, to warrant informational publication of
this mechanism.
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3. Conventions
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 BCP 14, RFC 2119
[RFC2119].
Throughout this document requirements for or references to proxy
servers or proxy behavior apply similarly to other intermediaries
within a Trust Domain (ex: B2BUAs).
The term Trust Domain in this document has the meaning as defined in
RFC 3324 [RFC3324].
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4. Syntax of the Header Fields
The following syntax specification uses the augmented Backus-Naur
Form (BNF) as described in RFC 4234 [RFC5234].
4.1. The P-Asserted-Service Header
The P-Asserted-Service header field is used among trusted SIP
entities (typically intermediaries) to carry the service information
of the user sending a SIP message.
The P-Asserted-Service header field carries information that is
derived service identification. While a declarative service
identification can assist in deriving the value transferred in this
header, this should be in the form of streamlining the correct
derived service identification.
PAssertedService = "P-Asserted-Service"
HCOLON PAssertedService-value
PAssertedService-value = Service-ID *(COMMA Service-ID)
See Section 4.4 for the definition of Service-ID in ABNF.
Proxies can (and will) add and remove this header field.
Table 1 extends the headers defined in this document to Table 2 in
SIP [RFC3261], Section 7.1 of the SIP-specific event notification
[RFC3265], tables 1 and 2 in the SIP INFO method [RFC2976], tables 1
and 2 in Reliability of provisional responses in SIP [RFC3262],
tables 1 and 2 in the SIP UPDATE method [RFC3311], tables 1 and 2 in
the SIP extension for Instant Messaging [RFC3428], table 1 in the SIP
REFER method [RFC3515] and tables 2 and 3 in the SIP PUBLISH method
[RFC3903]:
Header field where proxy ACK BYE CAN INV OPT REG SUB
_______________________________________________________________
P-Asserted-Service R admr - - - o o - o
Header field NOT PRA INF UPD MSG REF PUB
_______________________________________________________________
P-Asserted-Service - - - - o o o
Table 1
There may be multiple P-Asserted-Service header fields. The
semantics of multiple P-Asserted-Service header fields appearing in
the same request is not defined.
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4.2. The P-Preferred-Service Header
The P-Preferred-Service header field is used from a user agent to a
trusted proxy to carry the preferred service of the user sending the
SIP request that the user wishes to be used for the P-Asserted-
Service field value that the trusted element will insert.
The P-Preferred-Service header field carries information that is
declarative service identification. Such information should only be
used to assist in deriving a derived service identification at the
recipient entity.
PPreferredService = "P-Preferred-Service"
HCOLON PPreferredService-value
PPreferredService-value = Service-ID *(COMMA Service-ID)
See Section 4.4 for the definition of Service-ID in ABNF.
Table 2 extends the headers defined in this document to Table 2 in
SIP [RFC3261], Section 7.1 of the SIP-specific event notification
[RFC3265], tables 1 and 2 in the SIP INFO method [RFC2976], tables 1
and 2 in Reliability of provisional responses in SIP [RFC3262],
tables 1 and 2 in the SIP UPDATE method [RFC3311], tables 1 and 2 in
the SIP extension for Instant Messaging [RFC3428], table 1 in the SIP
REFER method [RFC3515] and tables 2 and 3 in the SIP PUBLISH method
[RFC3903]:
Header field where proxy ACK BYE CAN INV OPT REG SUB
_______________________________________________________________
P-Preferred-Service R dr - - - o o - o
Header field NOT PRA INF UPD MSG REF PUB
_______________________________________________________________
P-Preferred-Service - - - - o o o
Table 2
There may be multiple P-Preferred-Service header fields. The
semantics of multiple P-Preferred-Service header fields appearing in
the same request is not defined.
4.3. Service and Application Definition
Definition of services and their characteristics is outside the scope
of this document. Other standards organizations, vendors and
operators may define their own services and register them.
A hierarchical structure is defined consisting of service identifiers
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or application identitifiers, subservice identifiers.
The service and subservice identifiers identify the service as
described in Section 1. The URN may also be used to identify a
service or an application between end users for use within the
context of RFC 3841 [RFC3841].
IANA maintains a registry of service identifier values that have been
assigned. This registry is created by the actions of Section 8.2 of
this document.
Subservice identifiers are not managed by IANA. It is the
responsibility of the organisation that registered the service to
manage the subservices.
4.4. Registration Template
Below, we include the registration template for the URN scheme
according to RFC 3406 [RFC3406]. The URN scheme is defined as an
informal NID.
Namespace ID: urn-xxx
Registration Information: Registration version: 1; registration
date: 2007-04-21
Declared registrant of the namespace: TBD
Declaration of syntactic structure: The URN consists of a
hierarchical service identifier or application identifier, with a
sequence of labels separated by periods. The left-most label is
the most significant one and is called 'top-level service
identifier', while names to the right are called 'sub-services' or
'sub-applications'. The set of allowable characters is the same
as that for domain names (see RFC 1123 [RFC1123]) and a subset of
the labels allowed in RFC 3958 [RFC3958]. Labels are case-
insensitive and MUST be specified in all lower-case. For any
given service identifier, labels can be removed right-to-left and
the resulting URN is still valid, referring a more generic
service, with the except of the top-level service identifier and
possibly the first sub-service or sub-application identifier. In
other words, if a service identifier 'w.x.y.z' exists, the URNs
'w.x' and 'w.x.y' are also valid service identifiers.
Service-ID = "urn-xxx:" urn-service-id
urn-service-id = top-level *("." sub-service-id)
top-level = let-dig [ *26let-dig ]
sub-service-id = let-dig [ *let-dig ]
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let-dig = ALPHA / DIGIT / "-"
While the naming convention above uses the term "service" all the
constructs are equally applicable to identifying applications
within the UA.
Note to RFC editor: replace xxx with the assigned 3 numeric digit
identifier.
Relevant ancillary documentation: None
Identifier uniqueness considerations: A service identifier
identifies a service, and an application identifier an application
indicated in the service or application registration (see IANA
Considerations (Section 8)). Uniqueness is guaranteed by the IANA
registration.
Identifier persistence considerations: The service or application
identifier for the same service is or application expected to be
persistent, although there naturally cannot be a guarantee that a
particular service will continue to be available globally or at
all times.
Process of identifier assignment: The process of identifier
assignment is described in the IANA Considerations (Section 8).
Process for identifier resolution: There is no single global
resolution service for service identifiers or application
identifiers.
Rules for Lexical Equivalence: 'service' identifiers are compared
according to case-insensitive string equality.
Conformance with URN Syntax: The BNF in the 'Declaration of
syntactic structure' above constrains the syntax for this URN
scheme.
Validation mechanism: Validation determines whether a given string
is currently a validly-assigned URN (see RFC 3406 [RFC3406]). Due
to the distributed nature of usage and since not all services are
available everywhere, validation in this sense is not possible
Scope: The scope for this URN can be local to a single domain, or
may be more widely used.
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5. Usage of the P-Preferred-Service and P-Asserted-Service header
fields
5.1. Usage of the P-Preferred-Service and P-Asserted-Service header
fields in Requests
5.1.1. Procedures at User Agent Clients (UAC)
The UAC MAY insert a P-Preferred-Service in a request that creates a
dialog, or a request outside of a dialog. This information can
assist the proxies in identifying appropriate service capabilities to
apply to the call. This information MUST NOT conflict with other SIP
or SDP information included in the request. Furthermore, the SIP or
SDP information needed to signal functionality of this service MUST
be present. Thus if a service requires a video component, then the
SDP has to include the media line associated with that video
component; it cannot be assumed from the P-Preferred-Service header
field value. Similarly if the service requires particular SIP
functionality for which a SIP extension and a Require header field
value is defined, then the request has to include that SIP signalling
as well as the P-Preferred-Service header field value.
5.1.2. Procedures at Intermediate Proxies
A proxy in a Trust Domain can receive a request from a node that it
trusts, or a node that it does not trust. When a proxy receives a
request from a node it does not trust and it wishes to add a
P-Asserted-Service header field, the proxy MUST identify the service
appropriate to the capabilities (e.g. SDP) in the request, MAY
authenticate the originator of the request (in order to determine
whether the user is subscribed for that service), and use the
identity which results from this checking and authentication to
insert a P-Asserted-Service header field into the request.
If the proxy receives a request from a node that it trusts, it can
use the information in the P-Asserted-Service header field, if any,
as if it had authenticated the user itself.
If there is no P-Asserted-Service header field present, or it is not
possible to match the request to a specific service as identified by
the service identifier, a proxy MAY add one containing it using its
own analysis of the information contained in the SIP request. If the
proxy received the request from an element that it does not trust and
there is a P-Asserted-Service header present, the proxy MUST replace
that header field contents with a new analysis or remove this header
field.
The analysis performed to identify such service identifiers is
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outside the scope of this document. However, it is perfectly valid
as a result of the analysis to not include any service identifier in
the forwarded required, and thus not include a P-Asserted-Service
header.
If a proxy forwards a request to a node outside the proxy's trust
domain, there MUST NOT be a P-Asserted-Service header field in the
forwarded request.
5.1.3. Procedures at User Agent Servers (UAS)
For a UAS outside the trust domain, the P-Asserted-Service header is
removed before it reaches this entity, therefore there are no
procedures for such a device.
However, if a User Agent Server receives a request from a previous
element that it does not trust, it MUST NOT use the P-Asserted-
Service header field in any way.
If a UA is part of the Trust Domain from which it received a request
containing a P-Asserted-Service header field, then it can use the
value freely but it MUST ensure that it does not forward the
information to any element that is not part of the Trust Domain.
5.2. Usage of the P-Preferred-Service and P-Asserted-Service header
fields in Responses
There is no usage of these header field in responses.
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6. Examples of Usage
In this example, proxy.example.com creates a P-Asserted-Service
header field from the user identity it discovered from SIP Digest
authentication, and the list of services appropriate to that user,
and the services that correspond to the SDP information included in
the request. It forwards this information to a trusted proxy which
forwards it to a trusted gateway. Note that these examples consist
of partial SIP messages that illustrate only those headers relevant
to the authenticated identity problem.
* F1 useragent.example.com -> proxy.example.com
INVITE sip:+14085551212@example.com SIP/2.0
Via: SIP/2.0/TCP useragent.example.com;branch=z9hG4bK-123
To: <sip:+14085551212@example.com>
From: "Anonymous" <sip:anonymous@anonymous.invalid>;tag=9802748
Call-ID: 245780247857024504
CSeq: 1 INVITE
Max-Forwards: 70
* F2 proxy.example.com -> useragent.example.com
SIP/2.0 407 Proxy Authorization
Via: SIP/2.0/TCP useragent.example.com;branch=z9hG4bK-123
To: <sip:+14085551212@example.com>;tag=123456
From: "Anonymous" <sip:anonymous@anonymous.invalid>;tag=9802748
Call-ID: 245780247857024504
CSeq: 1 INVITE
Proxy-Authenticate: .... realm="sip.example.com"
* F3 useragent.example.com -> proxy.example.com
INVITE sip:+14085551212@example.com SIP/2.0
Via: SIP/2.0/TCP useragent.example.com;branch=z9hG4bK-124
To: <sip:+14085551212@example.com>
From: "Anonymous" <sip:anonymous@anonymous.invalid>;tag=9802748
Call-ID: 245780247857024504
CSeq: 2 INVITE
Max-Forwards: 70
Proxy-Authorization: .... realm="sip.example.com" user="fluffy"
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* F4 proxy.example.com -> proxy.pstn.example (trusted)
INVITE sip:+14085551212@proxy. pstn.example SIP/2.0
Via: SIP/2.0/TCP useragent.example.com;branch=z9hG4bK-124
Via: SIP/2.0/TCP proxy.example.com;branch=z9hG4bK-abc
To: <sip:+14085551212@example.com>
From: "Anonymous" <sip:anonymous@anonymous.invalid>;tag=9802748
Call-ID: 245780247857024504
CSeq: 2 INVITE
Max-Forwards: 69
P-Asserted-Service: "urn-xxx:example-telephony.version1"
* F5 proxy.pstn.example -> gw.pstn.example (trusted)
INVITE sip:+14085551212@gw.pstn.example SIP/2.0
Via: SIP/2.0/TCP useragent.example.com;branch=z9hG4bK-124
Via: SIP/2.0/TCP proxy.example.com;branch=z9hG4bK-abc
Via: SIP/2.0/TCP proxy.pstn.example;branch=z9hG4bK-a1b2
To: <sip:+14085551212@example.com>
From: "Anonymous" <sip:anonymous@anonymous.invalid>;tag=9802748
Call-ID: 245780247857024504
CSeq: 2 INVITE
Max-Forwards: 68
P-Asserted-Service: urn-xxx:exampletelephony.version1
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7. Security considerations
The mechanism provided in this document is a partial consideration of
the problem of service identification in SIP. For example, these
mechanisms provide no means by which end users can securely share
service information end-to-end without a trusted service provider.
This information is secured by transitive trust, which is only as
reliable as the weakest link in the chain of trust.
The trust domain provides a set of servers where the characteristics
of the service are agreed for that service identifier value, and that
the calling user is entitled to use that service.
draft-ietf-sipping-service-identification
[I-D.ietf-sipping-service-identification] identifies the impact of
allowing such service identifier values to "leak" outside of the
trust domain, including implications on fraud, interoperability and
stifling of service innovation.
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8. IANA considerations
8.1. P-Asserted-Service and P-Preferred-Service header fields
This document specifies two new SIP headers: P-Asserted-Service and
P-Preferred-Service. Their syntax is given in Section 3. These
headers are defined by the following information, which has been
added to the header sub-registry under
http://www.iana.org/assignments/sip-parameters.
Header Name compact Reference
----------------- ------- ---------
P-Asserted-Service [RFCxxxx]
P-Preferred-Service [RFCxxxx]
Note to the RFC editor: substitute xxxx with the RFC number of this
document.
8.2. Definition of Service-ID values
top-level identifiers are identified by labels managed by IANA,
according to the processes outlined in RFC 5226 [RFC5226] in a new
registry called "Service-ID/Application-ID Labels". Thus, creating a
new service at the top-level requires IANA action. The policy for
adding service labels is 'specification required'. The following two
identifiers are initially defined:
3gpp-service
3gpp-application
Subservice identifiers are not managed by IANA. It is the
responsibility of the organisation that registered the service to
manage the subservices.
Application identifiers are not managed by IANA. It is the
responsibility of the organisation that registered the service to
manage the applicable applications.
Entries in the registration table have the following format:
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Service/Application Reference Description
--------------------------------------------------------------------
3gpp-service RFCxxx Communication services defined by
3GPP for use by the IM CN subsystem
and its attached UAs
3gpp-application RFCxxx Applications defined by 3GPP for
use by UAs attached to the IM CN
subsystem
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9. APPENDIX: Changes history
Note to RFC Editor: Please remove this entire appendix before
publication
9.1. Changes between version -01 and version -02
1. Incorporation of terms "derived service identification" and
"declarative service identification" from
draft-ietf-sipping-service-identification.
2. Correction of the URN syntax in examples.
3. Appropriate introduction to table 1 and table 2 placing these in
a normative context to those in other tables in other RFCs.
4. Addition to security considerations section to clarify trust
domain concept.
5. References to RFC 3325 changed to RFC 3324 for definition of
trust domain.
6. Reference to RFC 2234 updated to RFC 5234 because the later
revision applies. No consequential technical change.
7. Reference to RFC 2434 updated to RFC 5226 because the later
revision applies. No consequential technical change.
8. References updated to symbolic. Remove of reference identifiers
from abstract.
9. Numerous editorial changes and minor clarifications.
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10. References
10.1. Normative References
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application
and Support", STD 3, RFC 1123, October 1989.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3324] Watson, M., "Short Term Requirements for Network Asserted
Identity", RFC 3324, November 2002.
[RFC3406] Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom,
"Uniform Resource Names (URN) Namespace Definition
Mechanisms", BCP 66, RFC 3406, October 2002.
[RFC3958] Daigle, L. and A. Newton, "Domain-Based Application
Service Location Using SRV RRs and the Dynamic Delegation
Discovery Service (DDDS)", RFC 3958, January 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
10.2. Informative References
[RFC2976] Donovan, S., "The SIP INFO Method", RFC 2976,
October 2000.
[RFC3262] Rosenberg, J. and H. Schulzrinne, "Reliability of
Provisional Responses in Session Initiation Protocol
(SIP)", RFC 3262, June 2002.
[RFC3265] Roach, A., "Session Initiation Protocol (SIP)-Specific
Event Notification", RFC 3265, June 2002.
[RFC3311] Rosenberg, J., "The Session Initiation Protocol (SIP)
UPDATE Method", RFC 3311, October 2002.
Drage Expires April 23, 2009 [Page 20]
Internet-Draft SIP Service Identification October 2008
[RFC3428] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C.,
and D. Gurle, "Session Initiation Protocol (SIP) Extension
for Instant Messaging", RFC 3428, December 2002.
[RFC3515] Sparks, R., "The Session Initiation Protocol (SIP) Refer
Method", RFC 3515, April 2003.
[RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
"Indicating User Agent Capabilities in the Session
Initiation Protocol (SIP)", RFC 3840, August 2004.
[RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
Preferences for the Session Initiation Protocol (SIP)",
RFC 3841, August 2004.
[RFC3903] Niemi, A., "Session Initiation Protocol (SIP) Extension
for Event State Publication", RFC 3903, October 2004.
[I-D.ietf-sipping-service-identification]
Rosenberg, J., "Identification of Communications Services
in the Session Initiation Protocol (SIP)",
draft-ietf-sipping-service-identification-03 (work in
progress), August 2008.
[I-D.rosenberg-sip-app-media-tag]
Rosenberg, J., "A Session Initiation Protocol (SIP) Media
Feature Tag for MIME Application Sub-Types",
draft-rosenberg-sip-app-media-tag-02 (work in progress),
November 2007.
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Author's Address
Keith Drage
Alcatel-Lucent
Quadrant, Stonehill Green, Westlea
Swindon, Wilts
UK
Email: drage@alcatel-lucent.com
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Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
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Drage Expires April 23, 2009 [Page 23]
