Re: [MMUSIC] RTSP timeout issue

[RÃmi Denis-Courmont <rem at videolan.org>]

Le Wednesday 05 September 2007 14:33:27 Magnus Westerlund, vous avez ÃcritÂ:
> The mandatory support of the RTSP one is implicit through the
> implementation of certain methods carrying session IDs. I will need to
> check if there needs more clarity here. The support of RTCP keep-alive
> is of course depending on the server using RTCP at all. But I think we
> should clarify the requirement that server supporting RTCP must refresh
> its session timers based on that feedback.

But then, how does the client know the server will understand RTCP 
keep-alives? One could argue that if the profile is AVP (or AVPF, SAVP, 
SAPVF, etc...), it's got to be the case, but I think it should be explicit.

Otherwise clients end up having to use RTSP always for safety.

> So I think it is impossible to have a single mandate. We will always
> have RTSP to fall back, and each individual media transport needs to
> decide if keep-alive can be done and then safely enough.

(...)
> Well, congestion control is already mandated. Go look in RTP and you
> will find that it points out the need for congestion control. From a
> strictly practical point. Any streaming server not using RTCP to monitor
> its transmission is stupid as the quality delivered to the client can't
> be ensured at all.

Stupid maybe, but it would be insane to mandate that any RTSP server would 
start transrating depending on the client bandwidth. Otherwise, you'd need 
one CPU per client for h264 streams ;)

> A reasonable approach is to at least monitor loss 
> rates on a medium turn and adapt based on that. Sure you will not be
> TCP-friendly that way, but you will at least not create total congestion
> collapse. I hope that the future will allow for better congestion
> control. But the reality for streaming is that in most case you don't
> have any serious issues with using congestion control thanks to the
> large buffer to smooth variations in.

That depends. I agree that most users will anyway stop the stream out of 
annoyance if there is noticeable congestion. However, we've had complaints 
from users that some RTSP servers kept streaming when a client lost 
connectivity without shutting down its session cleanly.

-- 
RÃmi Denis-Courmont

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