Subject: RE: [Sipping] Media grouping in transcoding framework

From: "Geir Arne Sandbakken" <[email-masked]>
Date: Fri, 11 Mar 2005 00:10:11 +0100

Let me try to use the example in the framework where an audio session is
upgraded to an audio/video where you want lip sync.  The existing audio
doesn't need transcoding, but the video does.  The transcoding (and
probably the different transport path) will introduce a delay for the
video compared to the directly delivered audio.  You may leave it to the
recipient to re-align the media streams, but you may easily over extend
the jitter buffer for the recipient or at least make the jitter buffer
less effective for real jitter.  

If I understand the framework correctly, this can only happen with 3pcc.
In the Conference Bridge Transcoding Model it will probably not happen
because all media streams will go by the conference bridge anyway.

What I was thinking about was in the lines of grouping inside of SDP for
lip sync would mandate that the streams would be handled in the same
manner,   but I would have to think more on this.

Geir Arne

  _____  

From: Medhavi Bhatia [mailto:[email-masked]] 
Sent: 10. mars 2005 13:59
To: Geir Arne Sandbakken; 'Gonzalo Camarillo'
Cc: 'SIPPING LIST'
Subject: RE: [Sipping] Media grouping in transcoding framework

I guess the document needs to get down to the detail of RTP sessions
being transcoded. Could you describe the jitter buffer problem in some
detail which happens when we transcode one of the RTP sessions in the
session. 

  _____  

From: [email-masked] [mailto:[email-masked]] On
Behalf Of Geir Arne Sandbakken
Sent: Thursday, March 10, 2005 1:20 PM
To: Gonzalo Camarillo
Cc: SIPPING LIST
Subject: [Sipping] Media grouping in transcoding framework

Gonzalo,

Just to recap our brief discussion.

The framework document talks about end-points invoking services on a
stream basis for the Third Party Call Control Transaction model. It
could be useful to have some language that addresses stream grouping in
the framework document.  One use case is audio and video lip sync.  You
might want the transcoder to handle both streams - even if one doesn't
need transcoding - to avoid over extending the jitter buffer for the
recipient.

Geir Arne 

_______________________________________________
Sipping mailing list  https://www1.ietf.org/mailman/listinfo/sipping
This list is for NEW development of the application of SIP
Use [email-masked] for questions on current sip
Use [email-masked] for new developments of core SIP

---

From: "Medhavi Bhatia" <[email-masked]>
Date: Thu, 10 Mar 2005 18:21:56 -0500

Not sure if you are assuming the conference bridge to be a single box doing
all transcoding. The signaling may be handled by a single entity, but the
media transcoding may be done by one or more separate boxes which are
controlled by the signaling entity. In this case, I still see the problem
you mention.

-Medhavi.

  _____  

From: Geir Arne Sandbakken [mailto:[email-masked]] 
Sent: Thursday, March 10, 2005 6:10 PM
To: Medhavi Bhatia; Gonzalo Camarillo
Cc: SIPPING LIST
Subject: RE: [Sipping] Media grouping in transcoding framework

Let me try to use the example in the framework where an audio session is
upgraded to an audio/video where you want lip sync.  The existing audio
doesn't need transcoding, but the video does.  The transcoding (and probably
the different transport path) will introduce a delay for the video compared
to the directly delivered audio.  You may leave it to the recipient to
re-align the media streams, but you may easily over extend the jitter buffer
for the recipient or at least make the jitter buffer less effective for real
jitter.  

What I was thinking about was in the lines of grouping inside of SDP for lip
sync would mandate that the streams would be handled in the same manner,
but I would have to think more on this.

Geir Arne

  _____  

I guess the document needs to get down to the detail of RTP sessions being
transcoded. Could you describe the jitter buffer problem in some detail
which happens when we transcode one of the RTP sessions in the session. 

  _____  

From: [email-masked] [mailto:[email-masked]] On Behalf
Of Geir Arne Sandbakken
Sent: Thursday, March 10, 2005 1:20 PM
To: Gonzalo Camarillo
Cc: SIPPING LIST
Subject: [Sipping] Media grouping in transcoding framework

Gonzalo,

The framework document talks about end-points invoking services on a stream
basis for the Third Party Call Control Transaction model. It could be useful
to have some language that addresses stream grouping in the framework
document.  One use case is audio and video lip sync.  You might want the
transcoder to handle both streams - even if one doesn't need transcoding -
to avoid over extending the jitter buffer for the recipient.

Geir Arne