Hi Sumin,
I just saw your message on sip implementors archive but didn't see the
answer. I also have the same question you raised. Please let me know if
you got the answer to your query.
Regards,
Sushil Kumar
<<<<<<<<<<<Your message in forum:>>>>>>>>>>>>>>
Hi all,
I have questions regarding ptime in SDP.
1) RFC 2327 says,
If a non-default (as defined in the RTP Audio/Video Profile)
packetisation is required, the "ptime" attribute is used as given
below.
It should not be necessary to know ptime to decode RTP or vat
audio, and it is intended as a recommendation for the
encoding/packetisation of audio.
[Q] does second paragraph mean that UAS should be able to decode
non-default packetisation audio packet without a ptime information?
[Q] if an offer sent by UAC doesn't have ptime, does it mean
that UAC will only send default packetisation audio packet or UAC will
be able to send non-default packetisation audio packet?
2) Media Negotiation.
[Q] Let's say that UAC use ptime=40 and UAS only supports ptime=20.
Basically UAS will reject UAC's offer with 488 response. But
Unfortunately, a supporting ptime value is different depending on UASs.
if UAC doesn't know which packetization which UAS supports and UAC want
to use non-default packetisation, UAC will keep sending requests with a
different ptime value. until negotiation succeed. How does UAC know if a
call request rejected because of ptime? And how UAC know what is a
maximum packetisation number which UAS allows? I found
draft-xu-mmusic-sdp-codec-param-01 which we can use for this purpose.
[Q] Is it possible that UAS adds sdp codec parameters to SDP in
answer instead of request rejection. Let's say that UAC set ptime to 40
and UAS only support 30 msec packetisation. In this case, can UAS add
ptime=30 to SDP in answer?
[Q] Let's say that UAS/UAC support ptime=40 and UAS/UAC describe
media for send and recv separately in SDP. is it possible that UAC set
ptime=20 for audio send by UAC in Offer and UAS set ptime=40 for audio
sent by UAS in Answer ?
Thanks in advance for your help.
Sumin.
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