[OpenSIPS-Users] Re-INVITE Switch

[Bogdan-Andrei Iancu]

Hi Doug,

when setting up a SIP call, you cannot tell if it's Voice or FAX.....Fax 
calls are established at Voice calls and then one party is doing 
re-INVITE to switch to T38. But the call is already established (through 
a certain provider, in your case) and you cannot do anything about.

Ugly solution will be to use the b2bua in the middle to detect (in 
ongoing call) the FAX case and to close the callee leg and to open a new 
callee leg via the proper provider. But the callee experience will be 
terrible (ringing, answering, hunging up, ringing again...). Not to 
mention that you need to put all the calls to b2bua just to catch the 
FAX case.

What I would do is to ask the callers to put some prefix to the dial 
number in order to indicate that they want a FAX service ;)

Regards,
Bogdan

Douglas Lane wrote:
> Hey guys,
>
> I have a requirement to switch traffic based on if the call is FAX or 
> not. Now our clients might not have gateways that can prefix the 
> destination number if a fax is detected, so I need to do something in 
> the core network.
>
> We have only 1 provider that is fully T.38 capable with a success rate 
> of 99.95% on termination and origination, so my idea is if a FAX is 
> detected, to switch the call to that provider for termination. The 
> problem I have is T.38 is normally only detected after the call has been 
> answered. Is there a way with MediaProxy or Asterisk to detect if its a 
> fax device, and then instruct opensips to setup the call via another 
> gateway?
>
> I realize this is a difficult question, but was hoping someone on the 
> list might have done it already.
>
> Thanks for all the help
>
> Thanks
> Doug
>
>
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>   


-- 
Bogdan-Andrei Iancu
www.voice-system.ro