Subject: [MMUSIC] RFC 3890: b=TIAS value when multiple payloads present in a media line

From: "Vavilapalli Srikanth-A19563" <[email-masked]>
Date: Fri, 5 Dec 2008 18:07:42 +0800

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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