[Live-devel] AmiNET110

Bryn Reeves breeves at avantisworld.com
Thu Feb 12 09:26:27 PST 2004

Cavalera Claudio wrote:
>> I suspect that he may have misunderstood your question.  You were (I
>> presume) asking if multicast RTP sessions could be played, using
>> RTSP for session control.  However, he might have thought that you
>> were asking if RTSP itself could use multicast - which, of course,
>> it can't, because RTSP runs over TCP.
> I thought that in theory RTSP could be used over udp. Am i wrong?

RTSP (Real Time Streaming Protocol) is the control channel - it carries
commands (play, fast-forward etc) from the client to the server, and
returns data like the SDP descriptions to the client. RTSP always uses a
point-to-point TCP connection.

RTP (Realtime Transport Protocol) carries the media data, one connection
per media subsession (each video, audio track). This connection can use
UDP and multicast. 

> But when you control with RTSP a multicast session, you change the
> parameters for every members on the group, right? For example if you
> issue pause then you pause for each user, no?  

I don't have any experience with RTSP and multicast, but I think that is
the case. I am not sure, but I was under the impression that systems
which used this type of setup used special measures to allow only one
client to use the control channel.

Rtsp.org's faq may have some useful links for you, although the "Higher
Level Protocols used with IP Multicast" link at ipmulticast.com is down
- the domain seems to have lapsed..



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