SIPPING S. Olson
Internet-Draft O. Levin
Expires: January 16, 2005 Microsoft Corporation
July 18, 2004
REFER extensions
draft-olson-sipping-refer-extensions-02
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of section 3 of RFC 3667. By submitting this Internet-Draft, each
author represents that any applicable patent or other IPR claims of
which he or she is aware have been or will be disclosed, and any of
which he or she become aware will be disclosed, in accordance with
RFC 3668.
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.
This Internet-Draft will expire on January 16, 2005.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
The REFER extensions presented in this draft are usage of Feature
parameters with REFER and the ability to suppress an implicit
subscription with REFER. The extensions have been discussed in
SIPPING WG and are targeted to become SIP WG items.
Olson & Levin Expires January 16, 2005 [Page 1]
Internet-Draft REFER Extensions July 2004
Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Using Feature Parameters with REFER . . . . . . . . . . . . . 5
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . 5
3.2 Definition . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3.1 isfocus Usage . . . . . . . . . . . . . . . . . . . . 5
3.3.2 Media Type Usage . . . . . . . . . . . . . . . . . . . 5
4. Suppressing the REFER Implicit Subscription . . . . . . . . . 6
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . 6
4.2 Motivation . . . . . . . . . . . . . . . . . . . . . . . . 6
4.3 Definition . . . . . . . . . . . . . . . . . . . . . . . . 6
4.4 Preventing Forking of REFER Requests . . . . . . . . . . . 7
4.5 Example . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . 12
Olson & Levin Expires January 16, 2005 [Page 2]
Internet-Draft REFER Extensions July 2004
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
Olson & Levin Expires January 16, 2005 [Page 3]
Internet-Draft REFER Extensions July 2004
2. Introduction
The REFER extensions presented in this draft are usage of Feature
parameters with REFER and the ability to suppress an implicit
subscription with REFER. The extensions have been discussed in
SIPPING WG and are targeted to become SIP WG items.
Olson & Levin Expires January 16, 2005 [Page 4]
Internet-Draft REFER Extensions July 2004
3. Using Feature Parameters with REFER
3.1 Introduction
This document extends REFER method defined in RFC-3515 [3] to be used
with feature parameters defined in [5].
3.2 Definition
The Refer-To BNF from RFC-3515:
Refer-To = ("Refer-To" / "r") HCOLON ( name-addr / addr-spec ) * (SEMI generic-param)
is extended to:
Refer-To = ("Refer-To" / "r") HCOLON ( name-addr / addr-spec ) * (SEMI refer-param)
refer-param = generic-param / feature-param
where feature-param is defined in Section 9 of [5].
3.3 Examples
3.3.1 isfocus Usage
The syntax below shows how the "isfocus" feature parameter can be
used by REFER-Issuer to tell the REFER-Recipient that the
REFER-Target is a conference focus and, consequently, sending an
INVITE will bring the REFER-Recipient into the conference:
Refer-To: sip:conf44@example.com;isfocus
3.3.2 Media Type Usage
The syntax below shows how a REFER-Issuer can tell the
REFER-Recipient that the REFER-Target supports audio and video and,
consequently, that a video and audio session can be established by
sending an INVITE to the REFER-Target:
Refer-To: sip:videophone@example.com;audio;video
Olson & Levin Expires January 16, 2005 [Page 5]
Internet-Draft REFER Extensions July 2004
4. Suppressing the REFER Implicit Subscription
4.1 Introduction
The REFER specification specifies that every REFER creates an
implicit subscription between the REFER-Issuer and the
REFER-Recipient. This document defines a new option tag,
"norefersub", which specifies that an implicit subscription for event
package refer should not be created as a result of accepting this
REFER request.
4.2 Motivation
The REFER specification mandates that every REFER creates an implicit
subscription between the REFER-Issuer and the REFER-Recipient. This
subscription results in at least one NOTIFY being sent from the
REFER-Recipient to the REFER-Issuer. The REFER-Recipient may choose
to cancel the implicit subscription with this NOTIFY. The
REFER-Issuer may choose to cancel this implicit subscription with an
explicit SUBSCRIBE (Expires: 0) after receipt of the initial NOTIFY
or by sending a 481 response to this initial NOTIFY request.
One purpose of requiring the implicit subscription and initial NOTIFY
is to allow for the situation where the REFER request gets forked and
the REFER-Issuer needs a way to see the multiple dialogs that may be
established as a result of the forked REFER. This is the same
approach used to handle forking of SUBSCRIBE [4] requests. Where the
REFER-Issuer explicitly specifies that forking not occur, the
requirement that an implicit subscription be established is
unnecessary.
Another purpose of the NOTIFY is to inform the REFER-Issuer of the
progress of the SIP transaction that results from the REFER at the
REFER-Recipient. In the case where the REFER-Issuer is already aware
of the progress of the requested operation, such as when the
REFER-Issuer has an explicit subscription to the dialog event package
at the REFER-Recipient, the implicit subscription and resultant
NOTIFY traffic related to the REFER can create an unnecessary network
overhead.
4.3 Definition
This document defines a new option tag, "norefersub", which specifies
that an implicit subscription for event package refer should not be
created as a result of accepting this REFER request.
The "norefersub" option tag MUST be used by the REFER-Issuer only
when the REFER-Issuer can be certain that the REFER request will not
Olson & Levin Expires January 16, 2005 [Page 6]
Internet-Draft REFER Extensions July 2004
be forked.
The REFER-Issuer can place the "norefersub" option tag either in the
Require header or in the Supported header of the REFER request,
subject to application requirements.
If the REFER-Issuer inserts the option tag in the Supported header
but the REFER-Recipient doesn't grant the suggestion, an implicit
subscription is created as in default case.
If the REFER-Issuer inserts the option tag in the Require header but
the REFER-Recipient is not willing to grant the request, the REFER
request is rejected.
If the REFER-Recipient is willing to grant the "norefersub" behavior
for the issued REFER request, it MUST insert a Supported: norefersub
header in the 2xx response to the REFER-Issuer. In this case no
dialog is created.
4.4 Preventing Forking of REFER Requests
The REFER specification allows for the possibility of forking a REFER
request which is sent outside of an existing dialog. The
REFER-Issuer can ensure that REFER doesn't get forked by sending
REFER to a REFER-Recipient which has GRUU properties according to
definitions of [7].
4.5 Example
An example of REFER which suppresses the implicit subscription is
shown below:
REFER sip:pc-b@tradewind.com SIP/2.0
Via: SIP/2.0/TCP issuer.tradewind.com;branch=z9hG4bK-a-1
From: <sip:a@tradewind.com>;tag=1a
To: <sip:pc-b@tradewind.com>
Call-ID: 1@issuer.tradewind.com
CSeq: 234234 REFER
Max-Forwards: 70
Refer-To: <sip:c@tradewind.com;method=INVITE>
Require: norefersub
Accept-Contact: *;audio;require
Contact: sip:a@issuer.tradewind.com
Content-Type: message/sipfrag
Content-Id: <1239103912039@issuer.tradewind.com>
Content-Length: ...
Olson & Levin Expires January 16, 2005 [Page 7]
Internet-Draft REFER Extensions July 2004
5. IANA Considerations
This document defines a new option tag, "norefersub", which specifies
that an implicit subscription for event package refer should not be
created as a result of accepting this REFER request. This option tag
is only meaningful for the REFER request defined in RFC3515.
Olson & Levin Expires January 16, 2005 [Page 8]
Internet-Draft REFER Extensions July 2004
6. Security Considerations
This extension doesn't introduce new security threads beyond those
identified and addressed in the core SIP specifications.
Olson & Levin Expires January 16, 2005 [Page 9]
Internet-Draft REFER Extensions July 2004
7. Acknowledgements
The authors would like to thank Sriram Parameswar for his ideas being
originally presented in draft-parameswar-sipping-norefersub-00 and
incorporated in this document.
8 References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] 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.
[3] Sparks, R., "The Session Initiation Protocol (SIP) Refer
Method", RFC 3515, April 2003.
[4] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[5] Rosenberg, J., "Indicating User Agent Capabilities in the
Session Initiation Protocol (SIP)",
draft-ietf-sip-callee-caps-03 (work in progress), January 2004.
[6] Rosenberg, J., Schulzrinne, H. and P. Kyzivat, "Caller
Preferences for the Session Initiation Protocol (SIP)",
draft-ietf-sip-callerprefs-10 (work in progress), October 2003.
[7] Rosenberg, J., "Obtaining and Using Globally Routable User Agent
(UA) URIs (GRUU) in the Session Initiation Protocol (SIP)",
draft-ietf-sip-gruu-02 (work in progress), July 2004.
Authors' Addresses
Sean Olson
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
USA
Phone: +1-425-707-2846
EMail: seanol@microsoft.com
Olson & Levin Expires January 16, 2005 [Page 10]
Internet-Draft REFER Extensions July 2004
Orit Levin
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
USA
Phone: +1-425-722-2225
EMail: oritl@microsoft.com
Olson & Levin Expires January 16, 2005 [Page 11]
Internet-Draft REFER Extensions July 2004
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights 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; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat 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 implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
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 (2004). 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
Internet Society.
Olson & Levin Expires January 16, 2005 [Page 12]