Re: [siprec] Review Request for draft-ram-siprec-metadata-format-01

 

> -----Original Message-----
> From: Charles Eckel (eckelcu) [mailto:eckelcu@cisco.com] 
> Sent: 17 March 2011 20:31
> To: Elwell, John; Paul Kyzivat (pkyzivat)
> Cc: siprec@ietf.org
> Subject: RE: [siprec] Review Request for 
> draft-ram-siprec-metadata-format-01
> 
> Please see single comment inline.
> 
> > -----Original Message-----
> > From: siprec-bounces@ietf.org [mailto:siprec-bounces@ietf.org] On
> Behalf Of Elwell, John
> > Sent: Tuesday, March 15, 2011 6:56 AM
> > To: Paul Kyzivat (pkyzivat)
> > Cc: siprec@ietf.org
> > Subject: Re: [siprec] Review Request for
> draft-ram-siprec-metadata-format-01
> > 
> > 
> > 
> > 
> > > -----Original Message-----
> > > From: Paul Kyzivat [mailto:pkyzivat@cisco.com]
> > > Sent: 15 March 2011 13:03
> > > To: Elwell, John
> > > Cc: siprec@ietf.org
> > > Subject: Re: [siprec] Review Request for
> > > draft-ram-siprec-metadata-format-01
> > >
> > > On 3/15/2011 7:22 AM, Elwell, John wrote:
> > >
> > > >>> 2. We perhaps need to think about mixed RS media streams,
> > > >> i.e., where several CS media streams have been mixed to
> > > >> produce a single RS media stream. In this case, the several
> > > >> Media Stream objects would all point to the same SDP label, I
> > > >> guess. This then brings into question the mode element (type
> > > >> streamMode) - why is this needed? The fact that several Media
> > > >> Stream objects (stream elements) point to the same label
> > > >> would imply there has been mixing, so the mode element seems
> > > >> to be redundant.
> > > >>
> > > >> My thinking is that situation is modeled as a single media
> > > >> stream with
> > > >> multiple participants.
> > > > [JRE] I was confused by section 4.5 of the metadata model
> > > draft. It does indeed seem to say that it represents an RS
> > > media stream:
> > > > "A Media Stream block shall have properties of media as
> > > seen by SRC and sent to SRS."
> > > > And hence your interpretation above would seem reasonable.
> > > On the other hand, in 4.5.2 it says:
> > > > "A Media Stream SHALL be associated with Participant and CS."
> > > > This misled me. Also in 4.5.1:
> > > > "Codec params - represents codec parameters of the CS media"
> > > > This also seemed to imply the Media Stream object relates
> > > to a CS media stream.
> > > > Perhaps some clarification is needed in the Metadata draft.
> > > > Anyway, assuming we go with your interpretation, I suppose
> > > what we end up with is that if streams are mixed (whether
> > > this be at an MCU, say, or just part of the SRC in order to
> > > send the streams to the SRS), the net result will be
> > > modelling as a single stream in the metadata. Is this a
> > > common understanding?
> > >
> > > You may have a point here - that things are somewhat ambiguous.
> > >
> > > If we have two distinct media streams in the CS, and they 
> are mixed
> > > together by the SRC before sending to the SRS, then they could be
> > > treated different ways:
> > >
> > > - The SRC could report this as a single media stream with multiple
> > > participants. But then it would have to report its 
> metadata as if it
> > > were a single stream from a mixer.
> > >
> > > - The SRC could report it as multiple media streams from 
> a metadata
> > > perspective, but map them all onto the same RS media stream.
> > > (This is a
> > > possibility I had never considered/recognized.)
> > >
> > > Is there a desire to support both? If so, the metamodel and
> mechanism
> > > will probably need some tweaking.
> > [JRE] Consider:
> > "REQ-009: The mechanism MUST support the ability for an SRC to
> >    deliver mixed audio streams from different parties of a given
> >    Communication Session to an SRS."
> > One particular case I believe this covers is the simple 
> 2-party call,
> where there are two media
> > streams, one from A to B and the other from B to A. The SRC 
> could mix
> the two together into a single
> > stream to the SRS. Certainly useful for bandwidth constrained
> environments, but not so friendly
> > towards speech analytics.
> > 
> > John (as individual)
> 
> Once the stream is mixed meaning all packets have the same SSRC and
> CSRC, I think there is no point in trying to represent it as anything
> other than a single stream. If the metadata can indicate all the
> individual participants in the mixed stream, that would be 
> great, but I
> doubt you will get this in all cases.
> If it is a single RTP stream with multiple identifiable media streams
> muxed together, then it would be good to model as independent streams.
> In this case the different streams could be uniquely identified by a
> SSRC or CSRC. 
[JRE] Yes, that might be a valid case (although I am not sure that CSRC would be appropriate). Actually, this is something we haven't considered at all - I will start a separate thread.

John (as individual)

> 
> Cheers,
> Charles
> 
> > 
> > >
> > > 	Thanks,
> > > 	Paul
> > >
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