rfc2543.txt

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Network Working Group                                          M. Handley
Request for Comments: 2543                                          ACIRI
Category: Standards Track                                  H. Schulzrinne
                                                              Columbia U.
                                                              E. Schooler
                                                                 Cal Tech
                                                             J. Rosenberg
                                                                Bell Labs
                                                               March 1999

                    SIP: Session Initiation Protocol

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 (1999).  All Rights Reserved.

IESG Note

   The IESG intends to charter, in the near future, one or more working
   groups to produce standards for "name lookup", where such names would
   include electronic mail addresses and telephone numbers, and the
   result of such a lookup would be a list of attributes and
   characteristics of the user or terminal associated with the name.
   Groups which are in need of a "name lookup" protocol should follow
   the development of these new working groups rather than using SIP for
   this function. In addition it is anticipated that SIP will migrate
   towards using such protocols, and SIP implementors are advised to
   monitor these efforts.

Abstract

   The Session Initiation Protocol (SIP) is an application-layer control
   (signaling) protocol for creating, modifying and terminating sessions
   with one or more participants. These sessions include Internet
   multimedia conferences, Internet telephone calls and multimedia
   distribution. Members in a session can communicate via multicast or
   via a mesh of unicast relations, or a combination of these.






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RFC 2543            SIP: Session Initiation Protocol          March 1999


   SIP invitations used to create sessions carry session descriptions
   which allow participants to agree on a set of compatible media types.
   SIP supports user mobility by proxying and redirecting requests to
   the user's current location. Users can register their current
   location.  SIP is not tied to any particular conference control
   protocol. SIP is designed to be independent of the lower-layer
   transport protocol and can be extended with additional capabilities.

Table of Contents

   1          Introduction ........................................    7
   1.1        Overview of SIP Functionality .......................    7
   1.2        Terminology .........................................    8
   1.3        Definitions .........................................    9
   1.4        Overview of SIP Operation ...........................   12
   1.4.1      SIP Addressing ......................................   12
   1.4.2      Locating a SIP Server ...............................   13
   1.4.3      SIP Transaction .....................................   14
   1.4.4      SIP Invitation ......................................   15
   1.4.5      Locating a User .....................................   17
   1.4.6      Changing an Existing Session ........................   18
   1.4.7      Registration Services ...............................   18
   1.5        Protocol Properties .................................   18
   1.5.1      Minimal State .......................................   18
   1.5.2      Lower-Layer-Protocol Neutral ........................   18
   1.5.3      Text-Based ..........................................   20
   2          SIP Uniform Resource Locators .......................   20
   3          SIP Message Overview ................................   24
   4          Request .............................................   26
   4.1        Request-Line ........................................   26
   4.2        Methods .............................................   27
   4.2.1      INVITE ..............................................   28
   4.2.2      ACK .................................................   29
   4.2.3      OPTIONS .............................................   29
   4.2.4      BYE .................................................   30
   4.2.5      CANCEL ..............................................   30
   4.2.6      REGISTER ............................................   31
   4.3        Request-URI .........................................   34
   4.3.1      SIP Version .........................................   35
   4.4        Option Tags .........................................   35
   4.4.1      Registering New Option Tags with IANA ...............   35
   5          Response ............................................   36
   5.1        Status-Line .........................................   36
   5.1.1      Status Codes and Reason Phrases .....................   37
   6          Header Field Definitions ............................   39
   6.1        General Header Fields ...............................   41
   6.2        Entity Header Fields ................................   42
   6.3        Request Header Fields ...............................   43



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RFC 2543            SIP: Session Initiation Protocol          March 1999


   6.4        Response Header Fields ..............................   43
   6.5        End-to-end and Hop-by-hop Headers ...................   43
   6.6        Header Field Format .................................   43
   6.7        Accept ..............................................   44
   6.8        Accept-Encoding .....................................   44
   6.9        Accept-Language .....................................   45
   6.10       Allow ...............................................   45
   6.11       Authorization .......................................   45
   6.12       Call-ID .............................................   46
   6.13       Contact .............................................   47
   6.14       Content-Encoding ....................................   50
   6.15       Content-Length ......................................   51
   6.16       Content-Type ........................................   51
   6.17       CSeq ................................................   52
   6.18       Date ................................................   53
   6.19       Encryption ..........................................   54
   6.20       Expires .............................................   55
   6.21       From ................................................   56
   6.22       Hide ................................................   57
   6.23       Max-Forwards ........................................   59
   6.24       Organization ........................................   59
   6.25       Priority ............................................   60
   6.26       Proxy-Authenticate ..................................   60
   6.27       Proxy-Authorization .................................   61
   6.28       Proxy-Require .......................................   61
   6.29       Record-Route ........................................   62
   6.30       Require .............................................   63
   6.31       Response-Key ........................................   63
   6.32       Retry-After .........................................   64
   6.33       Route ...............................................   65
   6.34       Server ..............................................   65
   6.35       Subject .............................................   65
   6.36       Timestamp ...........................................   66
   6.37       To ..................................................   66
   6.38       Unsupported .........................................   68
   6.39       User-Agent ..........................................   68
   6.40       Via .................................................   68
   6.40.1     Requests ............................................   68
   6.40.2     Receiver-tagged Via Header Fields ...................   69
   6.40.3     Responses ...........................................   70
   6.40.4     User Agent and Redirect Servers .....................   70
   6.40.5     Syntax ..............................................   71
   6.41       Warning .............................................   72
   6.42       WWW-Authenticate ....................................   74
   7          Status Code Definitions .............................   75
   7.1        Informational 1xx ...................................   75
   7.1.1      100 Trying ..........................................   75
   7.1.2      180 Ringing .........................................   75



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RFC 2543            SIP: Session Initiation Protocol          March 1999


   7.1.3      181 Call Is Being Forwarded .........................   75
   7.1.4      182 Queued ..........................................   76
   7.2        Successful 2xx ......................................   76
   7.2.1      200 OK ..............................................   76
   7.3        Redirection 3xx .....................................   76
   7.3.1      300 Multiple Choices ................................   77
   7.3.2      301 Moved Permanently ...............................   77
   7.3.3      302 Moved Temporarily ...............................   77
   7.3.4      305 Use Proxy .......................................   77
   7.3.5      380 Alternative Service .............................   78
   7.4        Request Failure 4xx .................................   78
   7.4.1      400 Bad Request .....................................   78
   7.4.2      401 Unauthorized ....................................   78
   7.4.3      402 Payment Required ................................   78
   7.4.4      403 Forbidden .......................................   78
   7.4.5      404 Not Found .......................................   78
   7.4.6      405 Method Not Allowed ..............................   78
   7.4.7      406 Not Acceptable ..................................   79
   7.4.8      407 Proxy Authentication Required ...................   79
   7.4.9      408 Request Timeout .................................   79
   7.4.10     409 Conflict ........................................   79
   7.4.11     410 Gone ............................................   79
   7.4.12     411 Length Required .................................   79
   7.4.13     413 Request Entity Too Large ........................   80
   7.4.14     414 Request-URI Too Long ............................   80
   7.4.15     415 Unsupported Media Type ..........................   80
   7.4.16     420 Bad Extension ...................................   80
   7.4.17     480 Temporarily Unavailable .........................   80
   7.4.18     481 Call Leg/Transaction Does Not Exist .............   81
   7.4.19     482 Loop Detected ...................................   81
   7.4.20     483 Too Many Hops ...................................   81
   7.4.21     484 Address Incomplete ..............................   81
   7.4.22     485 Ambiguous .......................................   81
   7.4.23     486 Busy Here .......................................   82
   7.5        Server Failure 5xx ..................................   82
   7.5.1      500 Server Internal Error ...........................   82
   7.5.2      501 Not Implemented .................................   82
   7.5.3      502 Bad Gateway .....................................   82
   7.5.4      503 Service Unavailable .............................   83
   7.5.5      504 Gateway Time-out ................................   83
   7.5.6      505 Version Not Supported ...........................   83
   7.6        Global Failures 6xx .................................   83
   7.6.1      600 Busy Everywhere .................................   83
   7.6.2      603 Decline .........................................   84
   7.6.3      604 Does Not Exist Anywhere .........................   84
   7.6.4      606 Not Acceptable ..................................   84
   8          SIP Message Body ....................................   84
   8.1        Body Inclusion ......................................   84



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RFC 2543            SIP: Session Initiation Protocol          March 1999


   8.2        Message Body Type ...................................   85
   8.3        Message Body Length .................................   85
   9          Compact Form ........................................   85
   10         Behavior of SIP Clients and Servers .................   86
   10.1       General Remarks .....................................   86
   10.1.1     Requests ............................................   86
   10.1.2     Responses ...........................................   87
   10.2       Source Addresses, Destination Addresses and
              Connections .........................................   88
   10.2.1     Unicast UDP .........................................   88
   10.2.2     Multicast UDP .......................................   88
   10.3       TCP .................................................   89
   10.4       Reliability for BYE, CANCEL, OPTIONS, REGISTER
              Requests ............................................   90
   10.4.1     UDP .................................................   90
   10.4.2     TCP .................................................   91
   10.5       Reliability for INVITE Requests .....................   91
   10.5.1     UDP .................................................   92
   10.5.2     TCP .................................................   95
   10.6       Reliability for ACK Requests ........................   95
   10.7       ICMP Handling .......................................   95
   11         Behavior of SIP User Agents .........................   95
   11.1       Caller Issues Initial INVITE Request ................   96
   11.2       Callee Issues Response ..............................   96
   11.3       Caller Receives Response to Initial Request .........   96
   11.4       Caller or Callee Generate Subsequent Requests .......   97
   11.5       Receiving Subsequent Requests .......................   97
   12         Behavior of SIP Proxy and Redirect Servers ..........   97
   12.1       Redirect Server .....................................   97
   12.2       User Agent Server ...................................   98
   12.3       Proxy Server ........................................   98
   12.3.1     Proxying Requests ...................................   98
   12.3.2     Proxying Responses ..................................   99
   12.3.3     Stateless Proxy: Proxying Responses .................   99
   12.3.4     Stateful Proxy: Receiving Requests ..................   99
   12.3.5     Stateful Proxy: Receiving ACKs ......................   99
   12.3.6     Stateful Proxy: Receiving Responses .................  100