draft-ietf-sip-refer-feature-param-01.txt   rfc4508.txt 
SIP Working Group O. Levin Network Working Group O. Levin
Internet-Draft Microsoft Corporation Request for Comments: 4508 Microsoft Corporation
Expires: July 17, 2006 A. Johnston Category: Standards Track A. Johnston
Tello Corporation Avaya
January 13, 2006 Conveying Feature Tags with the
Session Initiation Protocol (SIP) REFER Method
Conveying Feature Tags with Session Initiation Protocol REFER Method
draft-ietf-sip-refer-feature-param-01
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document extends the REFER method, defined in RFC 3515, to The SIP "Caller Preferences" extension defined in RFC 3840 provides a
convey feature parameters defined in RFC 3840. mechanism that allows a SIP request to convey information relating to
the originator's capabilities and preferences for handling of that
request. The SIP REFER method defined in RFC 3515 provides a
mechanism that allows one party to induce another to initiate a SIP
request. This document extends the REFER method to use the mechanism
of RFC 3840. By doing so, the originator of a REFER may inform the
recipient as to the characteristics of the target that the induced
request is expected to reach.
Table of Contents Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction ....................................................2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology .....................................................2
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Definitions .....................................................3
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Examples ........................................................3
4.1. isfocus Feature Tag Usage . . . . . . . . . . . . . . . . . 4 4.1. isfocus Feature Tag Usage ..................................3
4.2. Voice and Video Feature Tags Usage . . . . . . . . . . . . 4 4.2. Voice and Video Feature Tags Usage .........................3
4.3. Example with URI parameters and multiple feature tags . . . 4 4.3. Example with URI parameters and multiple feature tags ......3
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations .........................................4
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 6. Acknowledgements ................................................4
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 7. Normative References ............................................4
8. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 7
1. Terminology
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].
To simplify discussions of the REFER method and its extensions, three
new terms are being used throughout the document:
o REFER-Issuer: the UA issuing the REFER request
o REFER-Recipient: the UA receiving the REFER request
o REFER-Target: the UA designated in the Refer-To URI
2. Introduction 1. Introduction
This document extends REFER method defined in RFC 3515 [3] to be used This document extends the SIP [2] REFER method defined in RFC 3515
with feature parameters defined in RFC 3840 [4]. [3] to be used with feature parameters defined in RFC 3840 [4].
Feature tags are used by a UA to convey to another UA information Feature tags are used by a UA to convey to another UA information
about capabilities and features. This information can be shared by a about capabilities and features. This information can be shared by a
UA using a number of mechanisms including registration requests, UA using a number of mechanisms, including REGISTER requests and
OPTIONS responses, or shared in the context of a dialog by inclusion responses and OPTIONS responses. This information can also be shared
with a remote target URI (Contact URI). in the context of a dialog by inclusion with a remote target URI
(Contact URI).
Feature tag information can be very useful to another UA. It is Feature tag information can be very useful to another UA. It is
especially useful prior to the establishment of a session. For especially useful prior to the establishment of a session. For
example, if a UA knows (through an OPTIONS query, for example) that example, if a UA knows (through an OPTIONS query, for example) that
the remote UA supports both video and audio, the calling UA might the remote UA supports both video and audio, the calling UA might
call offering video in the SDP. Another example is when a UA knows call, offering video in the SDP. Another example is when a UA knows
that a remote UA is acting as a focus and hosting a conference. In that a remote UA is acting as a focus and hosting a conference. In
this case, the UA might first subscribe to the conference URI and this case, the UA might first subscribe to the conference URI and
find out details about the conference prior to sending an INVITE to find out details about the conference prior to sending an INVITE to
join. join.
This extension to the REFER method provides a mechanism by which the This extension to the REFER method provides a mechanism by which the
REFER-Issuer can provide this useful information about the REFER- REFER-Issuer can provide this useful information about the REFER-
Target capabilities and functionality to the REFER-Recipient by Target capabilities and functionality to the REFER-Recipient by
including feature tags in the Refer-To header field in a REFER including feature tags in the Refer-To header field in a REFER
request. request.
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [1].
To simplify discussions of the REFER method and its extensions, three
new terms are used throughout the document:
o REFER-Issuer: the UA issuing the REFER request
o REFER-Recipient: the UA receiving the REFER request
o REFER-Target: the UA designated in the Refer-To URI
3. Definitions 3. Definitions
The Refer-To BNF from RFC 3515: The Refer-To BNF from RFC 3515:
Refer-To = ("Refer-To" / "r") HCOLON ( name-addr / addr-spec ) Refer-To = ("Refer-To" / "r") HCOLON ( name-addr / addr-spec )
* (SEMI generic-param) * (SEMI generic-param)
is extended to: is extended to:
Refer-To = ("Refer-To" / "r") HCOLON ( name-addr / addr-spec ) Refer-To = ("Refer-To" / "r") HCOLON ( name-addr / addr-spec )
* (SEMI refer-param) * (SEMI refer-param)
refer-param = generic-param / feature-param refer-param = generic-param / feature-param
where feature-param is defined in Section 9 of RFC 3840 [4]. where feature-param is defined in Section 9 of RFC 3840 [4].
Note that if any URI parameters are present, the entire URI must be Note that if any URI parameters are present, the entire URI must be
enclosed in "&amp;lt" and "&gt". If no "&lt" and "&gt" are present, all enclosed in "&lt;" and ">". If the "<" and ">" are not present, all
parameters after the URI are header parameters, not URI parameters. parameters after the URI are header parameters, not URI parameters.
4. Examples 4. Examples
4.1. isfocus Feature Tag Usage 4.1. isfocus Feature Tag Usage
The example below shows how the "isfocus" feature tag can be used by The example below shows how the "isfocus" feature tag can be used by
REFER-Issuer to tell the REFER-Recipient that the REFER-Target is a REFER-Issuer to tell the REFER-Recipient that the REFER-Target is a
conference focus and, consequently, sending an INVITE will bring the conference focus and, consequently, that sending an INVITE will bring
REFER-Recipient into the conference: the REFER-Recipient into the conference:
Refer-To: sip:conf44@example.com;isfocus Refer-To: sip:conf44@example.com;isfocus
4.2. Voice and Video Feature Tags Usage 4.2. Voice and Video Feature Tags Usage
The example below shows how a REFER-Issuer can tell the REFER- The example below shows how a REFER-Issuer can tell the REFER-
Recipient that the REFER-Target supports audio and video and, Recipient that the REFER-Target supports audio and video and,
consequently, that a video and audio session can be established by consequently, that a video and audio session can be established by
sending an INVITE to the REFER-Target: sending an INVITE to the REFER-Target:
Refer-To: "Alice's Videophone" <sip:alice@videophone.example.com> Refer-To: "Alice's Videophone" <sip:alice@videophone.example.com>
;audio;video ;audio;video
4.3. Example with URI parameters and multiple feature tags 4.3. Example with URI parameters and multiple feature tags
The example below shows how the REFER-Issuer can tell the REFER- The example below shows how the REFER-Issuer can tell the REFER-
Recipient that the REFER-Target is a voicemail server. Note that the Recipient that the REFER-Target is a voicemail server. Note that the
transport URI parameter is enclosed within the "&lt" and "&gt" so transport URI parameter is enclosed within the "<" and ">" so that it
that it is not interpreted as a header parameter. is not interpreted as a header parameter.
Refer-To: <sip:alice-vm@example.com;transport=tcp> Refer-To: <sip:alice-vm@example.com;transport=tcp>
;actor="msg-taker";automata;audio ;actor="msg-taker";automata;audio
5. IANA Considerations 5. Security Considerations
None.
6. Security Considerations
Feature tags can provide sensitive information about a user or a UA. Feature tags can provide sensitive information about a user or a UA.
As such, RFC 3840 cautions against providing sensitive information to As such, RFC 3840 cautions against providing sensitive information to
another party. Once this information is given out, any use may be another party. Once this information is given out, any use may be
made of it, including relaying to a third party as in this made of it, including relaying to a third party as in this
specification. specification.
A REFER-Issuer MUST NOT create or guess feature tags - instead a A REFER-Issuer MUST NOT create or guess feature tags. Instead, a
feature tag included in a REFER SHOULD have been discovered in an feature tag included in a REFER SHOULD be discovered in an
authenticated and secure method (such as an OPTIONS response or from authenticated and secure method (such as an OPTIONS response or from
a remote target URI in a dialog) directly from the REFER-Target. a remote target URI in a dialog) directly from the REFER-Target.
It is RECOMMENDED that the REFER-Issuer includes in the Refer-To It is RECOMMENDED that the REFER-Issuer includes in the Refer-To
header field all feature tags that were listed in the most recent header field all feature tags that were listed in the most recent
Contact header field of the REFER-Target. Contact header field of the REFER-Target.
A feature tag provided by a REFER-Issuer can not be authenticated or A feature tag provided by a REFER-Issuer can not be authenticated or
certified directly from the REFER request. As such, the REFER- certified directly from the REFER request. As such, the REFER-
Recipient MUST treat the information as hint. If the REFER-Recipient Recipient MUST treat the information as a hint. If the REFER-
application logic or user's action depends on the presence of the Recipient application logic or user's action depends on the presence
expressed feature, the feature tag can be verified. For example, in of the expressed feature, the feature tag can be verified. For
order to do so, the REFER-Recipient can directly send an OPTIONS example, in order to do so, the REFER-Recipient can directly send an
query to the REFER-Target over a secure (e.g. mutually authenticated OPTIONS query to the REFER-Target over a secure (e.g., mutually
and integrity protected) connection. This protects the REFER- authenticated and integrity-protected) connection. This protects the
Recipient against incorrect or malicious feature tags being sent. REFER-Recipient against the sending of incorrect or malicious feature
tags.
7. Acknowledgements 6. Acknowledgements
The authors would like to thank Jonathan Rosenberg for providing The authors would like to thank Jonathan Rosenberg for providing
helpful guidance to this work. helpful guidance to this work.
8. Normative References 7. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., [2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002. Session Initiation Protocol", RFC 3261, June 2002.
[3] Sparks, R., "The Session Initiation Protocol (SIP) Refer [3] Sparks, R., "The Session Initiation Protocol (SIP) Refer
Method", RFC 3515, April 2003. Method", RFC 3515, April 2003.
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Authors' Addresses Authors' Addresses
Orit Levin Orit Levin
Microsoft Corporation Microsoft Corporation
One Microsoft Way One Microsoft Way
Redmond, WA 98052 Redmond, WA 98052
USA USA
Phone: 425-722-2225 Phone: 425-722-2225
Email: oritl@microsoft.com EMail: oritl@microsoft.com
Alan Johnston Alan Johnston
Tello Corporation Avaya
999 Baker Way, Suite 250 St. Louis, MO 63124
San Mateo, CA 94404
Email: ajohnston@tello.com EMail: ajohnston@ipstation.com
Intellectual Property Statement Full Copyright Statement
Copyright (C) The Internet Society (2006).
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
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
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The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
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This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM 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.
Copyright Statement
Copyright (C) The Internet Society (2006). 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.
Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is provided by the IETF
Internet Society. Administrative Support Activity (IASA).
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