[AVT] RE: Doubts in draft-ietf-avt-rfc2429-bis-09.txt

Frederick,
The picture size and MPI parameter specify receiver capability (see in
the text from 2429bis bellow), it does not imply what will be sent since
asymmetry is allowed. So if the answerer specified CIF=1 it means that
it can receive CIF at upto 30 frames per second, it must only send QCIF
at 15 frames per second on lower.
So both answers are correct.

The sentence from RFC2429 means that if the offer specified QCIF=2 it
means that it can receive SQCIF=2 or lower but not SQCIF=1. It does not
say what resolution and at which frame rate it will send.

>From 2429bis

Picture sizes and MPI:

   Supported picture sizes and their corresponding minimum picture
interval (MPI) information for H.263 can be combined.  All picture sizes
can be advertised to the other party, or only a subset of it. Terminal
announces only those picture sizes (with their MPIs) which it is willing
to receive.  For example, MPI=2 means that maximum(decodable) picture
rate per second is about 15.

Roni

> -----Original Message-----
> From: Huve, Frederic [mailto:frederic.huve@hp.com]
> Sent: Tuesday, November 28, 2006 6:01 PM
> To: Even, Roni
> Cc: AVT WG
> Subject: Doubts in draft-ietf-avt-rfc2429-bis-09.txt
> 
> Roni,
> 
> We're investigating to move from RFC 2429 support to rfc2419-bis-09
> support and it remains one question around Offer/Answer. (I've browsed
> the mail archive and partially found part of the response
> http://www1.ietf.org/mail-archive/web/avt/current/msg06890.html :)
> 
> In the following use case, what is the valid SDP Offer/Answer scenario
?
> 
> If an offerer sends a SDP offer (meaning he wants to receive QCIF with
> MPI = 2):
> 
> m=video 8000 RTP/AVP 96
> a=rtpmap:96 H263-1998/90000
> a=fmtp:96 QCIF=2
> a=sendrecv
> 
> The answerer sends the following SDP answer (means that he can receive
> up to CIF with MPI = 1):
> 
> m=video 8002 RTP/AVP 96
> a=rtpmap:96 H263-1998/90000
> a=fmtp:96 CIF=1
> a=sendrecv
> 
> IMHO this scenario is not valid because of the RFC-2429bis statement:
"
> A system that declares support of a specific MPI for one of the
> resolutions SHALL also implicitly support a lower resolution with the
> same MPI."
> 
> In order to be compliant the answerer should instead responds with the
> following SDP answer:
> 
> m=video 8002 RTP/AVP 96
> a=rtpmap:96 H263-1998/90000
> a=fmtp:96 CIF=2
> a=sendrecv
> 
> 
> Warm thanks for your time !
> Regards,
> Frederic
> 
> frederic.huve@hp.com
> 
> 
> 
> 
> 
>
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