Subject: RTSP to DMIF mapping

From: Florin Lohan <[email-masked]>
Date: Tue, 30 May 2000 23:32:20 +0300

Hello !
My name is Florin Lohan and I am a PhD student at Tampere University of
Technology, Finland. In cooperation with Nokia, we are working in order
to improve our proposal for the management of MPEG-4 session using IETF
protocols. Our first approach is described in the MPEG document N3198p4,
"Text for ISO/IEC 14496-1 version 3 VM 9.0".
We are trying to map the DMIF control commands to RTSP/SDP protocols.
Our goal is to obtain interoperability with RTSP clients/servers.
I am kindly asking you to help me with the following problem regarding a
standard RTSP server behavior:
DMIF, the  has separate commands for opening and closing a session
(ServiceAttach and ServiceDetach). After a session is opened, a client
can add and delete media channels (streams) at will. So it can happen
that a client opens a session, opens some media streams, then closes
them all, and  in the same DMIF session, it opens some other media
streams. According to MPEG, the DMIF session should remain "alive"
during this process.
My question is how an RTSP server should behave when a client  closes
all opened media streams inside its session. Is the server closes  the
session with the client after the last media stream is closed or is it
still keeping it opened for some time (until the timeout expires, maybe)
?
Thank you and best regards,
Florin Lohan

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From: Dave Singer <[email-masked]>
Date: Wed, 31 May 2000 09:03:08 +0200

I guess my question is:  does it matter if you get a new RTSP session 
when you start re-opening streams?  It seems that the only danger is 
that the resource that is the target of the URL may change while you 
have no session open, so if you do not do a new DESCRIBE, you might 
be out of sync with the target of the URL.

-- 
David Singer
Apple Computer/QuickTime

---

From: Anup Rao <[email-masked]>
Date: Mon, 05 Jun 2000 19:11:58 -0700

> still keeping it opened for some time (until the timeout expires, maybe)

Florin,

A session  is valid until a TEARDOWN on the presentation URL (see section 12.37)
or a timeout.  So one should be able to start a session with the first SETUP,
setup and subsequently teardown 1..n streams within the presentation,  have no
stream on at one point in time, and subsequently start n+1... streams within the
same presentation.  To end the session, a TEARDOWN is done on the presentation
URL. However this is hardly typical -  usually the entire point of a
presentation is  to aggregate streams that are viewed/heard together.

The key here is that you can do it within what is considered by the
client-server  pair as *one presentation*. That is somewhat different than
starting a "generic" session, playing any number of streams/presentations and
then closing the session.

-Anup.