On 5/19/14 10:58 AM, Rajesh wrote:
Hi,
In the below call flow, when the UAC and UAS can start transmitting RTP
packets. I think RTP session can be started after UAS receives PRACK for
180 ringing. I would really appreciate your opinion on this. Thanks
The use of 180rel doesn't alter when RTP can start. From the UAC's
perspective it can still start toward the UAC as soon as the INVITE is
sent. From the UAS perspective it can't start toward the UAC until the
UAS has received the offer (the INVITE). There is no reason why the UAS
must wait for the prack. However the UAS might *want* to wait for the
prack before starting to send, since that gives it more assurance that
things are in good shape.
For instance, if something in the middle is gating the flow of RTP in
both directions until the answer is received, then waiting for the prack
will avoid early media being dropped.
Thanks,
Paul
UAC -> UAS (Invite)
UAS -> UAC (100 trying)
UAS -> UAC (180 Ringing Require 100rel header is set) includes SDP Body
UAC -> UAS (PRACK to 180 Ringing)
UAS -> UAC (200 OK to PRACK)
UAS -> UAC (200 OK to invite) No SDP
UAC -> UAS (ACK to 200 OK for invite)
Regards
Rajesh
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