David Benoit wrote:
> On Fri, Oct 02, 2009 at 04:22:55PM -0400, Dale Worley wrote:
>> On Thu, 2009-10-01 at 10:37 +0200, DE CLERCQ Johan wrote:
>>> As we all know, in ISDN you can detect when you go to a voicemailbox of
>>> a cellular line by looking for the PROGRES message as defined in Q.931.
>> There is no good way to do this in SIP. However, an answering automaton
>> "should" identify itself with the "automata" media feature tag on its
>> Contact header:
>>
>> Contact: <sip:u...@pc.example.com>;automata
That would be indication of any sort of automaton.
If you want to know it is really a VM server, you would be looking for:
Contact: <sip:u...@pc.example.com>;automata;actor="msg-taker"
(Again, see 3840)
(Its "msg-taker" to cover recording of media other than audio.)
But I suspect there are a lot of VM systems that don't signal this.
Thanks,
Paul
>> See RFC 3840.
>
> Even the inclusion of this tag isn't fool proof. Consider the case of user
> with voicemail screening. The call is initially directed to an automata but a
> human listening in to the recording decides to take the call. A human has
> answered, but some filtering was applied. Or a caller interrogation service
> that collects information about the caller for users who refuse calls from
> private numbers. This would also be initially answered by an automata, but
> could ultimately be answered by a human.
>
> If you are solely looking for whether you were directed to voicemail, I would
> look more into the diversion headers and the information you get there. They
> will tell you the reason the call was forwarded where it was going before.
> Have a look at http://tools.ietf.org/html/draft-levy-sip-diversion-10
>
> David
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