20 mar 2010 kl. 16.40 skrev Iñaki Baz Castillo:
> 2010/3/20 Olle E. Johansson <[email protected]>:
>
>>> 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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