3 apr 2011 kl. 13.23 skrev Iñaki Baz Castillo:
> 2011/3/31 Olle E. Johansson <o...@edvina.net>:
>> If you are sending only ringback, I would recommend sending 180 with SDP
>> instead of 183. If you're sending 183, I can't move my state machine to
>> ringing state, which would help a lot of 3rd party apps. If you send
>> ringback in 183 - they won't notice the ringing and would see the call going
>> from calling state directly to answer, which is confusing. Sending ringback
>> with 183 and not sending 180 is a problem for many apps.
>>
>> Use 183 only if you have an operator message to play. Otherwise, add SDP to
>> the 180 Ringing.
>
> Hi Olle. So you propose that ringback (just pure ringback with no
> voice announcement) should be always sent in a 180 response (with or
> without SDP, as usually SIP phones generate 180 with no SDP, of
> course).
Yes. I am not saying that you should always send ringback with 180, but if you
do want to send ringback in audio, use 180.
>
> And just use 183 (always with SDP for sure) when the media contains an
> announcement ("the number you are calling is not available" and so).
exactly.
>
> Am I right?
Yes.
183 doesn't say much about the state change, but 180 is actually a state change
indicating that something is alerting the target about an incoming call. This
is very important in gateway situations, like a b2bua like Asterisk.
/O
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