rfc2976.txt

283个中文RFC文档

Network Working Group                                        S. Donovan
Request for Comments: 2976                                  dynamicsoft
Category: Standards Track                                  October 2000


                          The SIP INFO 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 (2000).  All Rights Reserved.

Abstract

   This document proposes an extension to the Session Initiation
   Protocol (SIP).  This extension adds the INFO method to the SIP
   protocol.  The intent of the INFO method is to allow for the carrying
   of session related control information that is generated during a
   session.  One example of such session control information is ISUP and
   ISDN signaling messages used to control telephony call services.

   This and other example uses of the INFO method may be standardized in
   the future.

Table of Contents

   1     Introduction................................................2
   1.1   Example Uses................................................2
   2     INFO Method.................................................3
   2.1   Header Field Support for INFO Method........................3
   2.2   Responses to the INFO Request Method........................4
   2.3   Message Body Inclusion......................................5
   2.4   Behavior of SIP User Agents.................................6
   2.5   Behavior of SIP Proxy and Redirect Servers..................6
   2.5.1 Proxy Server................................................6
   2.5.2 Forking Proxy Server........................................6
   2.5.3 Redirection Server..........................................6
   3.    INFO Message Bodies.........................................6
   4.    Guidelines for extensions making use of INFO................7
   5.    Security Considerations.....................................7
   6.    References..................................................8



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RFC 2976                    SIP INFO Method                 October 2000


   7.    Acknowledgments.............................................8
   8.    Author's Address............................................8
         Full Copyright Statement....................................9

1. Introduction

   The SIP protocol described in [1] defines session control messages
   used during the setup and tear down stages of a SIP controlled
   session.

   In addition, the SIP re-INVITE can be used during a session to change
   the characteristics of the session.  This is generally to change the
   properties of media flows related to the session or to update the SIP
   session timer.

   However, there is no general-purpose mechanism to carry session
   control information along the SIP signaling path during the session.

   The purpose of the INFO message is to carry application level
   information along the SIP signaling path.

   The INFO method is not used to change the state of SIP calls, or the
   parameters of the sessions SIP initiates.  It merely sends optional
   application layer information, generally related to the session.

   It is necessary that the mid-session signaling information traverse
   the post session setup SIP signaling path.  This is the path taken by
   SIP re-INVITEs, BYEs and other SIP requests that are tied to an
   individual session.  This allows SIP proxy servers to receive, and
   potentially act on, the mid-session signaling information.

   This document proposes an extension to SIP by defining the new INFO
   method.  The INFO method would be used for the carrying of mid-call
   signaling information along the session signaling path.

   1.1 Example Uses

      The following are a few of the potential uses of the INFO message:

      - Carrying mid-call PSTN signaling messages between PSTN
        gateways.

      - Carrying DTMF digits generated during a SIP session.

      - Carrying wireless signal strength information in support of
        wireless mobility applications.

      - Carrying account balance information.



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      - Carrying images or other non streaming information between the
        participants of a session.

      These are just potential uses; this document does not specify such
      uses nor does it necessarily recommend them.

      It can also be envisioned that there will be other telephony and
      non-telephony uses of the INFO method.

2. INFO Method

   The INFO method is used for communicating mid-session signaling
   information along the signaling path for the call.

   The INFO method is not used to change the state of SIP calls, nor
   does it change the state of sessions initiated by SIP.  Rather, it
   provides additional optional information which can further enhance
   the application using SIP.

   The signaling path for the INFO method is the signaling path
   established as a result of the call setup.  This can be either direct
   signaling between the calling and called user agents or a signaling
   path involving SIP proxy servers that were involved in the call setup
   and added themselves to the Record-Route header on the initial INVITE
   message.

   The mid-session information can be communicated in either an INFO
   message header or as part of a message body.  The definition of the
   message body and/or message headers used to carry the mid-session
   information is outside the scope of this document.

   There are no specific semantics associated with INFO.  The semantics
   are derived from the body or new headers defined for usage in INFO.

   2.1 Header Field Support for INFO Method

      Tables 1 and 2 add a column to tables 4 and 5 in the [1].  Refer
      to Section 6 of [1] for a description of the content of the
      tables.  Note that the rules defined in the enc. and e-e columns
      in tables 4 and 5 in [1] also apply to use of the headers in the
      INFO request and responses to the INFO request.










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   2.2 Responses to the INFO Request Method

      If a server receives an INFO request it MUST send a final
      response.

      A 200 OK response MUST be sent by a UAS for an INFO request with
      no message body if the INFO request was successfully received for
      an existing call.  Beyond that, no additional operations are
      required.

          Header                    Where    INFO
          ------                    -----    ----
          Accept                      R       o
          Accept-Encoding             R       o
          Accept-Language             R       o
          Allow                      200      -
          Allow                      405      o
          Authorization               R       o
          Call-ID                    gc       m
          Contact                     R       o
          Contact                    1xx      -
          Contact                    2xx      -
          Contact                    3xx      -
          Contact                    485      -
          Content-Encoding            e       o
          Content-Length              e       o
          Content-Type                e       *
          CSeq                       gc       m
          Date                        g       o
          Encryption                  g       o
          Expires                     g       o
          From                       gc       m
          Hide                        R       o
          Max-Forwards                R       o
          Organization                g       o

          Table 1 Summary of header fields, A-0

      Handling of INFO messages that contain message bodies is outside
      the scope of this document.  The documents defining the message
      bodies will also need to define the SIP protocol rules associated
      with those message bodies.

      A 481 Call Leg/Transaction Does Not Exist message MUST be sent by
      a UAS if the INFO request does not match any existing call leg.






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      If a server receives an INFO request with a body it understands,
      but it has no knowledge of INFO associated processing rules for
      the body, the body MAY be rendered and displayed to the user. The
      INFO is responded to with a 200 OK.

      If the INFO request contains a body that the server does not
      understand then, in the absence of INFO associated processing
      rules for the body, the server MUST respond with a 415 Unsupported
      Media Type message.

          Header                    Where    INFO
          ------                    -----    ----
          Priority                    R       o
          Proxy-Authenticate         407      o
          Proxy-Authorization         R       o
          Proxy-Require               R       o
          Require                     R       o
          Retry-After                 R       -
          Retry-After            404,480,486  o
          Retry-After                503      o
          Retry-After              600,603    o
          Response-Key                R       o
          Record-Route                R       o
          Record-Route               2xx      o