Subject: Relationship between RTSP URL and transport

From: Alagu Periyannan <[email-masked]>
Date: Mon, 16 Jun 1997 17:09:48 -0700

Hi all,

Say I want to control an audio/video presentation with one RTSP URL,
i.e. do the SETUP, PLAY, etc. on one URL instead of one for audio
and one for video.

Then does that mean I have to use the same transport (RTP session)
for both the audio and video media data?

Unless we can send back 2 transport headers in the SETUP and the
response to the SETUP I don't see how the audio and video media
data can be sent in different RTP sessions.

Hence, if we are using RTP as the transport mechanism, is it
correct in assuming that I need to control the audio and video
with separate RTSP URLs?

---------------------------------------------------
Alagu Periyannan                   [email-masked]

Interactive Multimedia Group
Apple Computer, Inc.

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From: Henning Schulzrinne <[email-masked]>
Date: Tue, 17 Jun 1997 08:11:36 -0400

> correct in assuming that I need to control the audio and video

Yes, a single RTSP session controls a single RTP stream. In some
circumstances, this RTP stream may contain several media (maybe it's an
MPEG transport stream).

Having a single RTSP session control several different (non-composite)
media streams was considered early on, but it gets really messy, as it
is hard to express the relationships between media streams without
inventing something like RTSL, possibly SDP or the SYMM description.
Thus, I'd expect to see a single URL, referring to a session description
of arbitrary complexity containing several RTSP URLs.

(Note: SYMM is the effort by the World-Wide Web Consortium to come up
with a common session/presentation/... description format. RTSL is
similar in some respects and part of the RealMedia SDK.)

-- 
Henning Schulzrinne         email: [email-masked]
Dept. of Computer Science   phone: +1 212 939-7042
Columbia University         fax:   +1 212 666-0140
New York, NY 10027          URL:   http://www.cs.columbia.edu/~hgs

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From: Stephen Casner <[email-masked]>
Date: Tue, 17 Jun 1997 12:43:11 -0700 ()

> of arbitrary complexity containing several RTSP URLs.

This makes sense.

> similar in some respects and part of the RealMedia SDK.)

Do you have a pointer to more information on SYMM?  (I didn't find it
at www.w3c.org or in a web search).

Is RTSL intended to become an open (IETF?) specification?  If not,
then I wonder about using it in examples in the RTSP specification.

Has anyone, particularly Mark Handley, thought about how RTSP URLs
might be added to an SDP session description?
							-- Steve