On 9/19/17 11:28 AM, Verma, Salil (Nokia - IN/Noida) wrote:
Hi ,
Please help me to understand the difference between 183 with SDP and without
SDP.
A 183 without SDP has no role in the offer/answer process. It mostly
just says "I'm working on your call." In the absence of the 100rel
option it has no other significance. If it also has 100rel then it
establishes an early dialog.
Is it really required to send 183 after invite r we can directly send 180
ringing ? In which all condition we have to send 183
If you want to send 180 to indicate that you are alerting then there is
no reason to also send 183. Just as with 183, the 180 may be sent with
or without SDP.
Note that the decision about whether to play early media at the UAC is
not determined by the reception of a 183. Rather it is governed by the
reception of media at the port in your offer, and can in principle occur
even without receiving a 18x of any sort. However some implementations
refuse to play early media until they receive an answer with an IP and
port that they use to verify the sender of the media. If you are doing
such validation, then it shouldn't matter what sort of 18x it is.
Thanks,
Paul
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