Conveying Feature Tags with the Session Initiation Protocol (SIP) REFER Method
RFC 4508

Document Type RFC - Proposed Standard (May 2006; No errata)
Last updated 2013-03-02
Replaces draft-olson-sipping-refer-extensions
Stream IETF
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Document shepherd No shepherd assigned
IESG IESG state RFC 4508 (Proposed Standard)
Telechat date
Responsible AD Allison Mankin
Send notices to dean.willis@softarmor.com, rohan@ekabal.com, fluffy@cisco.com
Network Working Group                                           O. Levin
Request for Comments: 4508                         Microsoft Corporation
Category: Standards Track                                    A. Johnston
                                                                   Avaya
                                                                May 2006

                    Conveying Feature Tags with the
             Session Initiation Protocol (SIP) REFER Method

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   The SIP "Caller Preferences" extension defined in RFC 3840 provides a
   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

   1. Introduction ....................................................2
   2. Terminology .....................................................2
   3. Definitions .....................................................3
   4. Examples ........................................................3
      4.1. isfocus Feature Tag Usage ..................................3
      4.2. Voice and Video Feature Tags Usage .........................3
      4.3. Example with URI parameters and multiple feature tags ......3
   5. Security Considerations .........................................4
   6. Acknowledgements ................................................4
   7. Normative References ............................................4

                            Standards Track                     [Page 1]
RFC 4508              Feature Tags with SIP REFER               May 2006

1.  Introduction

   This document extends the SIP [2] REFER method defined in RFC 3515
   [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
   about capabilities and features.  This information can be shared by a
   UA using a number of mechanisms, including REGISTER requests and
   responses and OPTIONS responses.  This information can also be shared
   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
   especially useful prior to the establishment of a session.  For
   example, if a UA knows (through an OPTIONS query, for example) that
   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
   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
   find out details about the conference prior to sending an INVITE to
   join.

   This extension to the REFER method provides a mechanism by which the
   REFER-Issuer can provide this useful information about the REFER-
   Target capabilities and functionality to the REFER-Recipient by
   including feature tags in the Refer-To header field in a REFER
   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

                            Standards Track                     [Page 2]
RFC 4508              Feature Tags with SIP REFER               May 2006

3.  Definitions

   The Refer-To BNF from RFC 3515:

   Refer-To = ("Refer-To" / "r") HCOLON ( name-addr / addr-spec )
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