Subject: [MMUSIC] RTSP: Synchronization information in regards to changed transport parameters

From: Magnus Westerlund <[email-masked]>
Date: Thu, 02 Oct 2003 17:08:09 +0200

Hi,

The previous week we had a discussion on the issue if there is 
meaningful to allow for the possibility to include Range and RTP-Info in 
SETUP response which changes the transport parameters for a media stream.

There where a good use reasons mentioned by Anders Klemets why this 
information should be present. As of a result of the discussion the 
below text has been drafted by me. Please review and comment if it is 
appropriate.

"A client {\MAY} issue a {\SETUP} request for a stream that is
already set up or playing in the session to change transport
parameters, which a server {\MAY} allow.  If it does not allow
this, it {\MUST} respond with error 455 (Method Not Valid In This
State). Reasons to support changing transport parameters, is to
allow for application layer mobility and flexibility to utilize
the best available transport as it becomes available.

In a {\SETUP} response for a request to change the transport
parameters while in Play state, the server {\SHOULD} include the
\header{Range} to indicate from what point the new transport
parameters are used. Further if RTP is used for delivery the
server {\SHOULD} also include the \header{RTP-Info} header to
indicate from what timestamp and RTP sequence number the change
has taken place. If both \header{RTP-Info} and \header{Range} is
included in the response the "rtp\_time" parameter and range
{\MUST} be for the corresponding time, i.e. be used in the same
way as for {\PLAY} to ensure the correct synchronization
information is present.

If the transport parameter change while in play state results in a
change of synchronization related information, for example
changing RTP SSRC, the server {\MUST} provide in the {\SETUP}
response the necessary synchronization information. However the
server is {\RECOMMENDED} to avoid changing the synchronization
information if possible."

Best Regards

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
----------------------------------------------------------------------
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: [email-masked]

_______________________________________________
mmusic mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/mmusic