[asterisk-dev] sip message 183 and ringback

[Olle E Johansson]

29 maj 2007 kl. 08.46 skrev Klaus Darilion:

> 183 means that early media is available. Thus, the party who sent  
> the 183 should also send media (e.g. ringback or busy tones).
>
> If a client sends 180 Ringing only, the ringback will be produced  
> by the caller.
>
> regards
> klaus
>
> dima wrote:
>> Hello everyone.
>> Please, could anyone explaing, if a 183 "Session in progress"  
>> message is
>> the only thing needed for generating ringback? Another question is  
>> where
>> do those ringbacks come from (who generates them?).
>> I'm having a wierd problem of not having ringback when dialing some
>> particular numbers (asterisk 1.2.18).

To generate a ringback to the caller Asterisk needs a ringing message  
from the
callee on the outbound call leg. Without that, Asterisk will not send  
a 180 ringing
message to the caller.

This is known to happen on some cell networks. If you know that you  
won't get
a ringing indication even though the callees phone is ringing, you  
can force
ringing either in the dialplan or with an option to dial.

/O