RFC 3515 (rfc3515) - Page 2 of 23

The Session Initiation Protocol (SIP) Refer Method

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

1. Overview

   This document defines the REFER method.  This SIP [1] extension
   requests that the recipient REFER to a resource provided in the
   request.

   This can be used to enable many applications, including Call
   Transfer.  For instance, if Alice is in a call with Bob, and decides
   Bob needs to talk to Carol, Alice can instruct her SIP user agent
   (UA) to send a SIP REFER request to Bob's UA providing Carol's SIP
   Contact information.  Assuming Bob has given it permission, Bob's UA
   will attempt to call Carol using that  contact.  Bob's UA will then
   report whether it succeeded in reaching the contact to Alice's UA.



Sparks                      Standards Track