Subject: Re: [MMUSIC] RFC 3890: b=TIAS value when multiple payloads

From: "Ingemar Johansson S" <[email-masked]>
Date: Mon, 8 Dec 2008 15:13:18 +0100

Hi

My 99 cents is that you need to pick the worst case like you do in your
example. 
An alternative that is IMHO a lot more attractive is to use the SDP
capability negotiation framework and its extensions (Media capabilities
and Miscellaneous capabilities. 
http://tools.ietf.org/wg/mmusic/draft-ietf-mmusic-sdp-capability-negotia
tion/
http://tools.ietf.org/wg/mmusic/draft-ietf-mmusic-sdp-media-capabilities
/

That would allow you to specify AS, TIAS, maxprate, ptime.... for each
alternative.

Regards
/Ingemar

> Date: Fri, 5 Dec 2008 18:07:42 +0800
> From: "Vavilapalli Srikanth-A19563" <[email-masked]>
> Subject: [MMUSIC] RFC 3890: b=TIAS value when multiple payloads
> 	present in a	media line
> To: "mmusic (E-mail)" <[email-masked]>
> Message-ID:
> 	<[email-masked]>
> Content-Type: text/plain; charset="us-ascii"
> 
> Hi
>  
> If there are more than one audio codec present in m= line in 
> SDP, what should the following SDP attributes represent?
>  
> 1) b=AS: The maximum of (application specific bandwidth for 
> any codec in the m=line)?
> 2) b=TIAS: The maximum of (bitrates for any codec in the m=line)?
> 3) a=maxprate: The maximum of (packet rates for any codec in 
> the m=line)?
> 4) a=ptime: The minimum of (packetization time for any codec 
> in the m=line)?
>  
> Please let me know if my understanding is correct or not.
>  
> For example if UAC wishes to offer two codecs G711A with 
> packetization of 20ms and bitrate of 64000bps and G728 with 
> packetization of 10ms and bitrate of 16000bps, then is the 
> following SDP correct?
>  
> m=audio 50000 RTP/AVP 8 98
> a=rtpmap:98 G728/8000
> b=AS:96    (considering 40 Bytes of overhead per packet)
> b=TIAS:64000
> a=maxprate:100
> a=ptime:10
>  
>  
> Regards
> Srikanth
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