Subject: Re: ANNOUNCE command

From: Anders Klemets <[email-masked]>
Date: Tue, 12 Aug 1997 18:27:50 -0700

I forgot to mention that there is a problem with the ANNOUNCE command
when the RTP data is being multicasted.  If a TCP connection is used
to control the multicasting server, only the client with the control
connection will be able to receive the ANNOUNCE commands.  Any clients
who are only receiving the multicasted RTP packets will be unaware of
mid-stream codec changes done by the server.

Hmm...  Maybe the RTSP draft editors meant that RTSP would be used
over multicast UDP in a scenario like this.  Hmm...  But I recall
reading in the draft that no RTSP acknowledgements should be sent
when using multicast UDP.  In that case, the clients would never get
the Transport-Info and Session-Id headers, because they are sent as
part of RTSP acknowledgements.  Maybe I got something wrong here,
so please let me know what your take on this is.

Anders

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From: Henning Schulzrinne <[email-masked]>
Date: Wed, 13 Aug 1997 07:29:42 -0400

> mid-stream codec changes done by the server.

For multicast, periodic retransmission is about the only real
possibility. However, I'm not sure we have worked out how a combined
unicast/multicast RTSP session would work. What multicast address should
the ANNOUNCEments be sent to and how do the clients find out about this
address? Shouldn't SDP/SAP be used instead?

-- 
Henning Schulzrinne        email: [email-masked]
Dept. of Computer Science  phone: +1 212 939-7042 (@Bell Labs: 908 949
8344)
Columbia University        fax:   +1 212 666-0140
New York, NY 10027         URL:   http://www.cs.columbia.edu/~hgs