Subject: Re: Relationship between RTSP URL and transport

From: Rob Lanphier <[email-masked]>
Date: Wed, 18 Jun 1997 15:10:46 -0700

At 12:43 PM 6/17/97 -0700, Stephen Casner wrote:
>Is RTSL intended to become an open (IETF?) specification?  If not,
>then I wonder about using it in examples in the RTSP specification.

You're right.  It probably isn't appropriate at this point.  RTSL was
originally designed to be the a replacement for the .ram files in
RealAudio, and it currently serves that purpose in the RealMedia SDK.  In
the current RealMedia SDK, we are using a format with the working name of
RTSP-MH (RTSP Media Header), which is a hierarchical format not entirely
unlike the SDF format that Henning proposed last fall.  The primary
difference is that RTSP-MH is SGML-based.

We've been playing with the idea of merging the two, but haven't entirely
reconciled that yet.

I think it would be entirely appropriate to start talking about SDP-NG (to
use a tired suffix).  In the meantime, you are also correct that we should
make sure that we nail down SDP usage in RTSP prior to coming up with
fanciful designs for replacements.

How would people here want RTSP/SDP to be used for container files such as
Quicktime files or ASF or RealMedia files?  I'll summarize the ideas that
we have for this at PN, but I'd like see what others think.  The issues are:

*  In the unicast case, the client must pick the port.  How should that 
   port assignment be done?
*  If the server is responsible for accessing each stream within the file as 
   a separate URL, how do the stream URLs get communicated back to the client?
   What do those URLs look like?
*  If the server doesn't have a separate URLs for each stream, how does the 
   client request the different streams?

All food for thought.  I'll post a strawman by the end of the week for
people to beat up on :)

Rob

---
Rob Lanphier               Voice: (206)674-2322         Fax: (206)674-2699
Program Manager-Protocols                         Email: [email-masked]
Progressive Networks-Home of RealAudio            Web: http://www.real.com
For more information on firewalls:       http://www.real.com/firewall.html
For more information on RTSP:               http://www.real.com/prognet/rt

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From: Alagu Periyannan <[email-masked]>
Date: Thu, 19 Jun 1997 14:39:56 -0700

>*  In the unicast case, the client must pick the port.  How should that

The SDP description can give a hint as to what port numbers to use.

The client can use the transport header in the SETUP to communicate
the actual port numbers to the RTSP server. The client will probably bind
to a dynamic port and let the local IP stack decide the port
number to be used. It must however make sure that the next higher
port number is also available for RTCP. Otherwise it should try
for another pair.

>   client request the different streams?

These are the same concerns that we have. This info. probably
needs to go into the SDP description as an "a=" tag.

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

Interactive Multimedia Group
Apple Computer, Inc.

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From: Alagu Periyannan <[email-masked]>
Date: Thu, 19 Jun 1997 14:39:56 -0700