I agree that it is better to return a 180 if you know that alerting is
happening. Unfortunately, the UAS doesn't always know that. Gateways in
particular may not know.
So the UAC has to be prepared to cope if the 180 doesn't arrive.
Thanks,
Paul
Olle E. Johansson wrote:
> 20 mar 2010 kl. 16.40 skrev Iñaki Baz Castillo:
>
>> 2010/3/20 Olle E. Johansson <o...@edvina.net>:
>>
>>>> For example, some TDM nodes fake the ringing and generate real audio.
>>>> When such TDM signaling arrives to a SIP-PSTN gateway, it must
>>>> generate a 183 with SDP :(
>>> NO, IT can generate 180 with SDP as default...
>> IMHO there is no difference at all between a 180 and 183 both with SDP.
> "180 ringing" is a state that I can relay to other protocols - we know that
> there's
> something out there that is in fact alerting the callee. 183 can be anything,
> normally translated as PROGRESS. In many apps, the ringing state is
> very important and it will be missed if we get no 180.
>
>> Does a 180 with SDP mean that the UAC could choose to render the real
>> audio or internal artificial ringing?
> Remember that the rendering might be something very different than audio.
>
>> If so, how the UAC would know if the received early media is just a
>> real ringing or a voice message "you have no credit to call, please
>> pay or die" ?
> Well, in my head the 180 with SDP means I'll get a ring signal in audio.
>
> 183 with SDP is something I would like to be limited to operator messages
> before an error code in the implementations, or just an informationial
> message before proceeding with ringing ("You need to refill your account
> soon"). Today, it's very often used for ringing and I can't determine if we
> actually have someone that is alerted on the other end.
>
> Especially with gateways to deaf people, it is very important to get an alert
> confirmation so that we can render the ringing in some way that works and we
> can move to a state where we are more prepared to activate a translator
> service. Sending 183 with audio doesn't help at all.
>
> /O
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