rfc2976.txt

283个中文RFC文档

          Route                       R       o
          Server                      r       o
          Subject                     R       o
          Timestamp                   g       o
          To                        gc(1)     m
          Unsupported                420      o
          User-Agent                  g       o
          Via                       gc(2)     m
          Warning                     r       o
          WWW-Authenticate           401      o

          Table 2 Summary of header fields, P-Z

      Bodies which imply a change in the SIP call state or the sessions
      initiated by SIP MUST NOT be sent in an INFO message.

      Other request failure (4xx), Server Failure (5xx) and Global
      Failure (6xx) responses MAY be sent for the INFO Request.

   2.3 Message Body Inclusion

      The INFO request MAY contain a message body.





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RFC 2976                    SIP INFO Method                 October 2000


   2.4 Behavior of SIP User Agents

      Unless stated otherwise, the protocol rules for the INFO request
      governing the usage of tags, Route and Record-Route,
      retransmission and reliability, CSeq incrementing and message
      formatting follow those in [1] as defined for the BYE request.

      An INFO request MAY be cancelled.  A UAS receiving a CANCEL for an
      INFO request SHOULD respond to the INFO with a "487 Request
      Cancelled" response if a final response has not been sent to the
      INFO and then behave as if the request were never received.

      However, the INFO message MUST NOT change the state of the SIP
      call, or the sessions initiated by SIP.

   2.5 Behavior of SIP Proxy and Redirect Servers

      2.5.1 Proxy Server

         Unless stated otherwise, the protocol rules for the INFO
         request at a proxy are identical to those for a BYE request as
         specified in [1].

      2.5.2 Forking Proxy Server

         Unless stated otherwise, the protocol rules for the INFO
         request at a proxy are identical to those for a BYE request as
         specified in [1].

      2.5.3 Redirection Server

         Unless stated otherwise, the protocol rules for the INFO
         request at a proxy are identical to those for a BYE request as
         specified in [1].

3. INFO Message Bodies

   The purpose of the INFO message is to carry mid-session information
   between SIP user agents.  This information will generally be carried
   in message bodies, although it can be carried in headers in the INFO
   message.

   The definition of the message bodies or any new headers created for
   the INFO method is outside the scope of this document.  It is
   expected that separate documents will be created to address
   definition of these entities.





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RFC 2976                    SIP INFO Method                 October 2000


   In addition, the INFO method does not define additional mechanisms
   for ensuring in-order delivery.  While the CSeq header will be
   incremented upon the transmission of new INFO messages, this should
   not be used to determine the sequence of INFO information.  This is
   due to the fact that there could be gaps in the INFO message CSeq
   count caused by a user agent sending re-INVITES or other SIP
   messages.

4. Guidelines for extensions making use of INFO

   The following are considerations that should be taken into account
   when defining SIP extensions that make use of the INFO method.

   - Consideration should be taken on the size of message bodies to be
     carried by INFO messages.  The message bodies should be kept small
     due to the potential for the message to be carried over UDP and the
     potential for fragmentation of larger messages.

   - There is potential that INFO messages could be forked by a SIP
     Proxy Server.  The implications of this forking of the information
     in the INFO message need to be taken into account.

   - The use of multi-part message bodies may be helpful when defining
     the message bodies to be carried by the INFO message.

   - The extensions that use the INFO message MUST NOT rely on the
     INFO message to do anything that effects the SIP call state or the
     state of related sessions.

   - The INFO extension defined in this document does not depend on
     the use of the Require or Proxy-Require headers.  Extensions using
     the INFO message may need the use of these mechanisms.  However,
     the use of Require and Proxy-Require should be avoided, if
     possible, in order to improve interoperability between SIP
     entities.

5. Security Considerations

   If the contents of the message body are private then end-to-end
   encryption of the message body can be used to prevent unauthorized
   access to the content.

   There are no other security issues specific to the INFO method.
   The security requirements specified in the SIP specification apply
   to the INFO method.






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RFC 2976                    SIP INFO Method                 October 2000


6. References

   [1] Handley, M., Schulzrinne, H., Schooler, E. and J. Rosenberg,
       "SIP: Session Initiation Protocol", RFC 2543, March 1999.

7. Acknowledgements

   The author would like to thank Matthew Cannon for his contributions
   to this document.  In addition, the author would like to thank the
   members of the MMUSIC and SIP working groups, especially Jonathan
   Rosenberg, for comments and suggestions on how to improve the
   document.

8. Author's Address

   Steve Donovan
   dynamicsoft
   5100 Tennyson Parkway, Suite 200
   Plano, Texas 75024

   Email: [e-mail]






























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RFC 2976                    SIP INFO Method                 October 2000


9.  Full Copyright Statement

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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