Re: [MMUSIC] MMT bandwidth limits (Re: comments on draft-holmberg-mmusic-sdp-mmt-negotiation-00)

> -----Original Message-----
> From: mmusic-bounces@ietf.org [mailto:mmusic-bounces@ietf.org] On
> Behalf Of Harald Alvestrand
> Sent: Monday, November 05, 2012 4:24 PM
> To: mmusic@ietf.org
> Subject: [MMUSIC] MMT bandwidth limits (Re: comments on draft-
> holmberg-mmusic-sdp-mmt-negotiation-00)
> 
> On 11/05/2012 04:29 AM, Charles Eckel (eckelcu) wrote:
> > In the case of multiple m-lines, you can assign a bandwidth per m-line and
> have the session bandwidth cap the total bandwidth for the session. With
> anymedia and a single m-line, you lose the granularity you previously had at
> the m-line level and are left with specifying the bandwidth for the
> anymedia line as a whole.
> > For example, today I might offer the following for a video call with content
> sharing:
> >
> > v=0
> > o=anonymous 1240218157 1240218157 IN IP4 10.193.128.35
> > s=-
> > i=myUserAgent
> > c=IN IP4 10.193.128.35
> > b=TIAS:512000
> > t=0 0
> > m=audio 6000 RTP/AVP 0 18 101
> > a=rtpmap:0 PCMU/8000
> > a=rtpmap:18 G729/8000
> > a=rtpmap:101 telephone-event/8000
> > a=fmtp:101 0-15
> > m=video 6002 RTP/AVP 96
> > b=TIAS:512000
> > a=rtpmap:96 H264/90000
> > a=fmtp:96 profile-level-id=428014
> > a=content:main
> > m=video 6002 RTP/AVP 96
> > b=TIAS:256000
> > a=rtpmap:96 H264/90000
> > a=fmtp:96 profile-level-id=428014
> > a=content:slides
> >
> > In this case, depending on the answer, the audio will take between 8k and
> 64k, the main video can take the remainder of the 512k until content sharing
> starts, and once content sharing starts, the main video could drop down a bit
> to free some bandwidth for the content .
> > With mmt, all I can specify is 512k for the total. I cannot subdivide it per
> media stream as above. To do so, I would need to specify some new SDP
> and/or encode the SSRC values I plan to use in SDP.
> I'm curious - if I send this in an offer, is there any part of the SDP
> description that says that the respondent, when sending, should cut down
> on his video bandwidth if video + audio would otherwise be > 512K?
> 
> I don't see any "priority" flags in there.

There is no explicit priority. It is up to the application to decide. RFC 3890 does say:

   At the SDP session level, the TIAS value is the maximal amount of
   bandwidth needed when all declared media streams are used.  This MAY
   be less than the sum of all the individual media streams values.
   This is due to the possibility that not all streams have their
   maximum at the same point in time. 

> (another thing that confuses me a bit is how b= represents bandwidth in
> the 2 directions for a point-to-point session - if A sends an offer with
> session b=TIAS:512K, and B sends A an answer with session b=TIAS:512K,
> and they both start sending video at 300K, are they below the cap or
> above the cap?

That is fine. This is just a statement of the maximum bandwidth the implementation is willing to receive. The values can be asymmetric, and this is just a maximum. It does not indicate anything about how much the implementation will send.

Cheers,
Charles

> Again, it's probably clear to those who've been around here for a while)

>                  Harald
> 
> 
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www.ietf.org/mailman/listinfo/mmusic