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MMUSIC                                                            T. Ura
Internet-Draft                                                    K. Oku
Intended status: Standards Track                                     NTT
Expires: May 15, 2008                                          H. Harada
                                                                 Hitachi
                                                            A. Kobayashi
                                                               NEC Corp.
                                                    M. Stiemerling (Ed.)
                                                         NEC Europe Ltd.
                                                       November 12, 2007


                     RTSP Asynchronous Notification
                   draft-stiemerling-rtsp-announce-00

Status of this Memo

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   This Internet-Draft will expire on May 15, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).








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Abstract

   Some IPTV deployments that are using the Real Time Streaming Protocol
   (RTSP) require the ability of the server to notify clients about
   asynchronous events occurring during an RTSP session.  Current
   deployments typically use the ANNOUNCE method of RTSP 1.0 for sending
   such asynchronous events from a server to clients by using some
   proprietary extensions.  However, the ANNOUNCE method has been
   removed from the current RTSP 2.0 draft, leaving the new
   specification without a mechanism for sending asynchronous messages
   from the server.  This memo describes a use case for such an
   asynchronous message and proposes a new RTSP 2.0 method.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Definition of Method . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  Normative Definitions  . . . . . . . . . . . . . . . . . .  5
     2.2.  Notice Header  . . . . . . . . . . . . . . . . . . . . . .  6
     2.3.  Limitations of ANNOUNCE  . . . . . . . . . . . . . . . . .  8
   3.  Feature Tag  . . . . . . . . . . . . . . . . . . . . . . . . .  9
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   5.  Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     6.1.  Normative References . . . . . . . . . . . . . . . . . . . 12
     6.2.  Informative References . . . . . . . . . . . . . . . . . . 12
   Appendix A.  Design Choices for Asynchronous Notifications . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
   Intellectual Property and Copyright Statements . . . . . . . . . . 16





















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1.  Introduction

   Some IPTV deployments that are using the Real Time Streaming Protocol
   (RTSP) require the ability of the server to ANNOUNCE clients about
   asynchronous events occurring during an RTSP session.  Such
   asynchronous events are, for example, termination of session or
   change (redirect) of the RTSP server.  While redirecting RTSP clients
   to a different RTSP server is well-described in RTSP 1.0 [RFC2326],
   end of stream or end of session by the server is not defined.

   Some RTSP 1.0 deployments are extending the ANNOUNCE method of
   [RFC2326], which is defined as:

      When sent from client to server, ANNOUNCE posts the description of
      a presentation or media object identified by the request URL to a
      server.  When sent from server to client, ANNOUNCE updates the
      session description in real-time.

   These implementations use ANNOUNCE to send asynchronous notifications
   for RTSP sessions from an RTSP server to RTSP clients.  The ANNOUNCE
   method is extended by adding a reason header, to indicate end of
   stream reason to the clients.  However, this extension of the
   ANNOUNCE method is not standardised.

   An example for a deployment using the extended ANNOUNCE method is the
   Hikari service provided by NTT in Japan [Hikari].  This service is
   based on the Hikari Service Architecture (HSA), developed by the
   Hikari Service Architecture Consortium (HSAC, [HSAC]) in Japan.  NB:
   The consortium itself was closed, as the service specification was
   completed, and the specification is currently used.  HSA is actually
   using the ANNOUNCE method as described above but does not use the
   client to server mode of it.

   The ANNOUNCE method has been removed in RTSP 2.0
   [I-D.ietf-mmusic-rfc2326bis], thus also having removed this way of
   sending asynchronous end of stream notifications to clients.  The
   current way in RTSP 2.0 of sending end of stream notifications is the
   REDIRECT method (see Section 11.9):

      The lack of a Location header in any REDIRECT request is
      indicative of the server no longer being able to fulfil the
      current request and having no alternatives for the client to
      continue with its normal operation.  It is akin to a server
      initiated TEARDOWN that applies both to sessions as well as the
      general connection associated with that client.

   The REDIRECT request does not include any reason header why the
   stream or the RTSP session is actually about to end.  Furthermore,



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   REDIRECT seems to be logically the wrong place for such a stream or
   session termination.

   Given the lack of a good and extensible semantics in the current RTSP
   2.0 draft for sending asynchronous notifications, we propose a new
   method in the next section.  The next section also discusses two
   different ways of including the new method in the RTSP 2.0
   specification.

   There was already an attempt to re-introduce the ANNOUNCE method
   described in [I-D.ietf-mmusic-rtsp-announce].  The goal of this draft
   was to revive ANNOUNCE for end of stream and change of session
   description.  This memo deliberately reuses some of ideas of
   [I-D.ietf-mmusic-rtsp-announce].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

































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2.  Definition of Method

   This section defines a new method for RTSP servers to asynchronously
   ANNOUNCE clients about end of stream or end of RTSP session with a
   reason code.  The new method is called ANNOUNCE, but any other
   suitable name is also possible (e.g., HALT, STOP, BYE), i.e., it is
   subject to further discussions.

   There are actually two ways of adding this extension to the RTSP
   protocol.  First, the ANNOUNCE method could be added directly to the
   core RTSP protocol or, second, it could be added as an extension to
   the core RTSP protocol.  This is also subject to WG discussions.

   The ANNOUNCE method is a mechanism for RTSP servers to signal RTSP
   clients about end of stream or end of RTSP session events.  ANNOUNCE
   is an RTSP request that can only be sent from servers to clients,
   thus requiring a persistent connection between server and client.
   Otherwise there is no way for the server to sent this request method
   to the client.  Therefore, clients are required to keep the RTSP
   connection to the server open at all times of an RTSP session.

   Here is an example RTSP conversation in which an RTSP server
   announces an end of stream event for a media stream using a non-
   aggregate URI.


       S->C: ANNOUNCE rtsp://foo.com/bar.avi/streamid=0 RTSP/2.0
             CSeq: 99
             Session: 12345678
             Notice: 2101 End-Of-Stream
             Range: npt=0-200
             RTP-Info: url=rtsp://foo.com/bar.avi/streamid=0;seq=45102

       C->S: RTSP/2.0 200 OK
             CSeq: 99
             Session: 12345678


2.1.  Normative Definitions

   The request-URI of an ANNOUNCE request can be either aggregate or
   non-aggregate URI.

   An ANNOUNCE request must include "CSeq" header and "Notice".  It MAY
   include the following optional headers:






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      "Range",

      "Session",

      "RTP-Info".

   An ANNOUNCE request MAY include an entity body, in which case it MUST
   follow the rules for entity body defined in Section 8.2 of
   [I-D.ietf-mmusic-rfc2326bis].  The entity body can be used to convey
   further details specific to an event type.  If the event type is end-
   of-stream or session termination announcement, the entity body MAY
   contain "text/parameter" content type that conveys the reason of the
   event.

   ANNOUNCE does NOT affect RTSP session state if the event type is
   "2101 End of Stream" but does affect the RTSP session state if the
   event type is "3000 End of Session".  If a receiver does not
   understand any of the headers in an ANNOUNCE request, it simply
   ignores those headers.

   The next section defines a new RTSP headers for ANNOUNCE method:
   "Notice".

2.2.  Notice Header

   This section defines a new mandatory header.  The Notice header is
   identifying the type of event pertaining to the ANNOUNCE request.

   The Notice header is defined in ABNF as:

             Notice           = "Notice" ":"  Notice
             Notice           = Notice-code SP Notice-string
             Notice-code      = 4DIGITS
             Notice-string    = token

      where:
          -- token is  defined in section 17 of [RTSP_NEW].


   The "Notice" header applies only the ANNOUNCE method, which is sent
   from server to client.

   The following pairs for Notice-code and Notice-string are defined in
   this memo.







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   +-------------+-------------------------+---------------------------+
   | Notice-code | Notice-string           | Description               |
   +-------------+-------------------------+---------------------------+
   | 1103        | Playout Stalled         | -/-                       |
   |             |                         |                           |
   | 1104        | Playout Resumed         | Temporarily stopped       |
   |             |                         |                           |
   | 2101        | End-of-Stream Reached   | Content terminated        |
   |             |                         |                           |
   | 2103        | Transition              | In transition             |
   |             |                         |                           |
   | 2104        | Start-of-Stream Reached | Returned to the initial   |
   |             |                         | content                   |
   |             |                         |                           |
   | 2306        | Continuous Feed         | Live finished             |
   |             | Terminated              |                           |
   |             |                         |                           |
   | 2401        | Ticket Expired          | Viewing right expired     |
   |             |                         |                           |
   | 4400        | Error Reading Content   | Data read error           |
   |             | Data                    |                           |
   |             |                         |                           |
   | 5200        | Server Resource         | Resource cannot be        |
   |             | Unavailable             | obtained                  |
   |             |                         |                           |
   | 5401        | Downstream Failure      | Stream could not be       |
   |             |                         | obtained                  |
   |             |                         |                           |
   | 5402        | Client Session          | -/-                       |
   |             | Terminated              |                           |
   |             |                         |                           |
   | 5403        | Server Shutting Down    | -/-                       |
   |             |                         |                           |
   | 5404        | Internal Server Error   | -/-                       |
   |             |                         |                           |
   | 5501        | End-of-Window_term      | -/-                       |
   |             |                         |                           |
   | 5502        | End-of-Contract_term    | -/-                       |
   +-------------+-------------------------+---------------------------+

                        Table 1: The Notice values

   If "Notice" is "2101 End-Of-Stream", the optional RTP-Info header
   SHOULD contain the "seq" attribute that indicates the sequence number
   of the next RTP packet.






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2.3.  Limitations of ANNOUNCE

   The server to client ANNOUNCE method is issued only if the server has
   the means to contact the client when it has information to push.
   This may not be possible if the RTSP connection between server and
   client is not persistent.  In such cases, the server will simply skip
   the sending of ANNOUNCE requests.  The server MUST NOT queue up the
   ANNOUNCE requests to be sent when client eventually connects.  Such a
   queue would unnecessarily complicate server implementations.










































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3.  Feature Tag

   The support of the ANNOUNCE method is represented by this feature
   tag:

      method.announce

   This feature tag applies to both servers and proxies.

   Implementations claiming "method.announce" feature tag MUST support
   the new "Notice" header defined in previous section.








































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4.  Security Considerations

   This initial version of this memo does not have yet any security
   considerations, but they will be added with the next revision.















































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5.  Conclusion

   This memo is work in progress and is requesting feedback from the
   MMUSIC working group .

   This memo needs to be further discussed to clarify these open issues:

   o  Should the proposed mechanism can be integrated in the current
      RTSP 2.0 specification or if it should be defined as an extension
      to the current RTSP 2.0 specification?

   o  The text mentions just RTSP server, but never clarifies the role
      of ANNOUNCE w.r.t.  RTSP proxies;

   o  Is the name ANNOUNCE appropriate for this method?

   o  The entity body should be better specified

   o  The only real reason codes are not very helpful yet.

   o  Exemplifying use cases are missing

   o  Extensibility section is missing

   o  IANA section is missing.


























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6.  References

6.1.  Normative References

   [I-D.ietf-mmusic-rfc2326bis]
              Schulzrinne, H., "Real Time Streaming Protocol 2.0
              (RTSP)", draft-ietf-mmusic-rfc2326bis-14 (work in
              progress), December 2006.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

6.2.  Informative References

   [HSAC]     "Hikari Service Architecture Consortium", Web Site http://
              web.archive.org/web/20040518075704/http://
              www.hikari-sac.org/, October 2007.

   [Hikari]   "Hikari Service Architecture", Web Site http://
              www.itu.int/itudoc/itu-t/com13/ipexpert/ipmedia/
              71304_pp7.ppt, October 2007.

   [I-D.ietf-mmusic-rtsp-announce]
              Zeng, T., "RTSP Announce Method",
              draft-ietf-mmusic-rtsp-announce-01 (work in progress),
              February 2005.

   [RFC2326]  Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time
              Streaming Protocol (RTSP)", RFC 2326, April 1998.






















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Appendix A.  Design Choices for Asynchronous Notifications

   Appendix A of [I-D.ietf-mmusic-rtsp-announce] discusses several
   design choices for implementing the ANNOUNCE method semantics with
   other methods of RTSP and also RTP.  We deem the arguments described
   as still valid and also applicable for the in this memo discussing
   the ANNOUNCE method.












































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Authors' Addresses

   Tetsuya Ura
   Nippon Telegraph and Telephone Corporation
   1-1 Hikarinooka
   Yokosuka-Shi Kanagawa  239-0847
   Japan

   Phone: +81 46 859 3780
   Email: ura.tetsuya@lab.ntt.co.jp


   Kenshin Oku
   Nippon Telegraph and Telephone Corporation
   1-1 Hikarinooka
   Yokosuka-Shi Kanagawa  239-0847
   Japan

   Phone: +81 46 859 2528
   Email: oku.kenshin@lab.ntt.co.jp


   Hiromi Harada
   Hitachi, Ltd.
   890 Kashimada
   Saiwai-ku Kawasaki-Shi Kanagawa  212-8567
   Japan

   Phone: +81 44 549 1578
   Email: hiromi.harada.jv@hitachi.com


   Akira Kobayashi
   NEC Corporation
   11-5 Shibaura 2-chone
   Minato-ku, Tokyo  108-8557
   Japan

   Phone: +81 3 5476 1084
   Email: a-kobayasi@ce.jp.nec.com











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   Martin Stiemerling
   NEC Europe Ltd. - NEC Laboratories Europe
   Kurfuerstenanlage 36
   Heidelberg  69115
   Germany

   Phone: +49 6221 4342 113
   Fax:   +49 6221 4342 155
   Email: stiemerling@nw.neclab.eu
   URI:   http://www.netlab.nec.de/









































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Full Copyright Statement

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