Subject: [MMUSIC] Re: [dccp] Using DCCP for VoIP

From: [email-masked]
Date: Fri, 25 Jul 2003 16:37:42 +0200

>Hi all,
>
>On this issue:
>
>> IMHO this issue is related to my question in the other mail about
>> managing audio AND video at the same time: probably DCCP should have a
>> way to handle "collectively" a bunch of streams, be it audio plus video
>> or two-way audio!
>
>Our thought was that, given DCCP's unreliability, it is trivial to layer
>multiple streams on top. The first byte of packet data could indicate
>stream number to the application. This works as long as both streams want
>to share the same congestion control state + CC mechanism -- is this the
>case?

a multiplex? (that would clash rather badly with the idea that RTP can be mapped
trivially using the port numbers !-)

One thing is sure, I have questions about how it would work with multiple DCCP "sessions":

If DCCP is running 2 sessions from host A to host B,
and at a given time DCCP tells *each* session "you have 200 kb/s"
=> does it mean the available bandwidth is 400 kb/s ?
but then the application could prefer to allocate +50 kb/s to audio
and +350 kb/s to video ...
=> or does it mean the total is 200 kb/s? but then DCCP would
have to assume that the 2 sessions are correctly managed (linked/grouped) so that
they dont "fight" for it, right? otherwise what a mess!

So the need is rather for a "grouping", like the API would enable
the application to tell DCCP: "these are 2 (or more) streams,
but it is a single CC "session", i.e. give me a single rate for the group
I will do the repartition". (same spirit as RTSP aggregate control)

regards

Philippe Gentric
Software Architect
Philips MP4Net
[email-masked]
http://www.platform4.philips.com

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