[Live-devel] AmiNET110

Cavalera Claudio Claudio.Cavalera at icn.siemens.it
Thu Feb 12 11:07:20 PST 2004

>-----Original Message-----
>From: Bryn Reeves [mailto:breeves at avantisworld.com] 
>Sent: giovedì 12 febbraio 2004 10.26
>To: LIVE.COM Streaming Media - development & use
>Subject: RE: [Live-devel] AmiNET110
>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.

I strongly agree to the point-to-point matter but RFC 2326 states that any protocol could be used under RTSP since it implements reliability in itself. Probably openRTSP does not implement it but I think that an URL beginning with rtspu://
exist to identify cases with unreliable transport.
However I myself don't consider this thing useful, maybe it can be used when you have to walk across some strange firewalls.

>> 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..

I've been looking for some information about multicast and didn't find much. Also the mailing list at multicasttech.com is dead and I'm not been able to find updated info on Reliable IP Multicast.


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