The Session Initiation Protocol (SIP) Refer Method
RFC 3515

Document Type RFC - Proposed Standard (April 2003; No errata)
Last updated 2013-03-02
Stream IETF
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Stream WG state (None)
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IESG IESG state RFC 3515 (Proposed Standard)
Telechat date
Responsible AD Allison Mankin
IESG note Approved in 2002-12-12 IESG meeting with just some fixes needed that Bert pointed out and that will be fixed with RFC Editor note:  time to stop using atlanta.com etc in favor of RFC 2606 example domains and need for boilerplate.  Chairs/author notified, they to let WG know.  RFC Editor Note given to Secretariat in hopes of announcement on 13 Dec.  [Note from Allison 2002-12-13]
Send notices to <dean.willis@softarmor.com>, <rohan@cisco.com>
Network Working Group                                          R. Sparks
Request for Comments: 3515                                   dynamicsoft
Category: Standards Track                                     April 2003

           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 (2003).  All Rights Reserved.

Abstract

   This document defines the REFER method.  This Session Initiation
   Protocol (SIP) extension requests that the recipient REFER to a
   resource provided in the request.  It provides a mechanism allowing
   the party sending the REFER to be notified of the outcome of the
   referenced request.  This can be used to enable many applications,
   including call transfer.

   In addition to the REFER method, this document defines the the refer
   event package and the Refer-To request header.

Table of Contents

   1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  The REFER Method . . . . . . . . . . . . . . . . . . . . . .  3
       2.1  The Refer-To Header Field . . . . . . . . . . . . . . .  3
       2.2  Header Field Support for the REFER Method . . . . . . .  4
       2.3  Message Body Inclusion. . . . . . . . . . . . . . . . .  5
       2.4  Behavior of SIP User Agents . . . . . . . . . . . . . .  6
            2.4.1 Forming a REFER request . . . . . . . . . . . . .  6
            2.4.2 Processing a REFER request. . . . . . . . . . . .  6
            2.4.3 Accessing the Referred-to Resource. . . . . . . .  6
            2.4.4 Using SIP Events to Report the Results
                  of the Reference. . . . . . . . . . . . . . . . .  7
            2.4.5 The Body of the NOTIFY. . . . . . . . . . . . . .  8
            2.4.6 Multiple REFER Requests in a Dialog . . . . . . .  9
            2.4.7 Using the Subscription-State Header
                  Field with Event Refer. . . . . . . . . . . . . .  9

Sparks                      Standards Track                     [Page 1]
RFC 3515                  The SIP Refer Method                April 2003

       2.5  Behavior of SIP Registrars/Redirect Servers . . . . . .  9
       2.6  Behavior of SIP Proxies . . . . . . . . . . . . . . . . 10
   3.  Package Details: Event refer . . . . . . . . . . . . . . . . 10
       3.1  Event Package Name. . . . . . . . . . . . . . . . . . . 10
       3.2  Event Package Parameters. . . . . . . . . . . . . . . . 10
       3.3  SUBSCRIBE Bodies. . . . . . . . . . . . . . . . . . . . 10
       3.4  Subscription Duration . . . . . . . . . . . . . . . . . 10
       3.5  NOTIFY Bodies . . . . . . . . . . . . . . . . . . . . . 11
       3.6  Notifier processing of SUBSCRIBE requests . . . . . . . 11
       3.7  Notifier Generation of NOTIFY Requests. . . . . . . . . 11
       3.8  Subscriber Processing of NOTIFY Requests. . . . . . . . 11
       3.9  Handling of Forked Requests . . . . . . . . . . . . . . 11
       3.10 Rate of Notifications . . . . . . . . . . . . . . . . . 11
       3.11 State Agents. . . . . . . . . . . . . . . . . . . . . . 11
   4.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 12
       4.1  Prototypical REFER callflow . . . . . . . . . . . . . . 12
       4.2  Multiple REFERs in a dialog . . . . . . . . . . . . . . 14
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . 16
       5.1  Constructing a Refer-To URI . . . . . . . . . . . . . . 16
       5.2  Authorization Considerations for REFER. . . . . . . . . 17
       5.3  Considerations for the use of message/sipfrag . . . . . 18
            5.3.1 Circumventing Privacy . . . . . . . . . . . . . . 18
            5.3.2 Circumventing Confidentiality . . . . . . . . . . 19
            5.3.3 Limiting the Breach . . . . . . . . . . . . . . . 19
            5.3.4 Cut, Paste and Replay Considerations. . . . . . . 19
   6.  Historic Material  . . . . . . . . . . . . . . . . . . . . . 20
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . 20
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . 21
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . 21
       9.1  Normative References. . . . . . . . . . . . . . . . . . 21
       9.2  Informative References. . . . . . . . . . . . . . . . . 21
   10. Intellectual Property Statement. . . . . . . . . . . . . . . 21
   11. Author's Address . . . . . . . . . . . . . . . . . . . . . . 22
   12. Full Copyright Statement . . . . . . . . . . . . . . . . . . 23
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