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
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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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