[Freeswitch-users] fax detection

[Tihomir Culjaga]

Hi Michael, thanks for your response.

i think it will be enough to check the call capability... we always know the
call is fax. We just need to apply the correct protocol :P


let's suppose you have 2 incoming calls:

   1. SDP containing G711, gsm, T.38 caps
   2. SDP containing G711, gsm caps


the caps will be known on within INVITE message and FS can act accordingly.

   - If there is no T.38 support within SDP, start fax application
   (SpanDSP).
   - If there is T.38 suport within the SDP, route the call to some
   predefined gateway meant for T.38 fax receiving.

In both cases, the fax should be received :P.

So, any chance to route the call according to T.38 caps within SDP message?



Now, for sending faxes there is some challenge.... we still have 2 calls:

we start sending a fax inband (SpanDSP) as this is the only thing we know...
and:

   - if we receive 200 OK with SDP containing G711, anyCaps => continue with
   InBand Fax
   - if we receive 200 OK with DSP containing anyCompressedCaps, T.38 =>
   drop the call without sending ACK to 200 OK ... and move the fax to be sent
   into a different directory.

well, as i said, while receiving faxes will work 100%, sending is tricky...
but it might work.

what do you guys think?

T.




On Thu, Sep 17, 2009 at 10:51 PM, Michael Collins <msc at freeswitch.org>wrote:

>
>
> On Tue, Sep 15, 2009 at 8:45 AM, Tihomir Culjaga <tculjaga at gmail.com>wrote:
>
>> Hi,
>>
>> is there any way to route fax calls according to the call capability?
>>
>> I mean .. if the fax call supports T.38 i'd like to route it to a T.38
>> capable gateway. All other fax calls (meaning inband) should be handled by
>> FS/SpanDSP.
>> Of course, I know that every fax call starts as a voice call and upon fax
>> tone detection additional capabilities are being negotiated(T.38 or G711).
>> Can it be done in early media, before the call is even answered?
>>
>> I don't claim to be an expert in all this, especially T.38, but if I
> understand correctly, in both cases the call needs to be answered first. I'm
> pretty sure that the sending fax machine won't start emitting the 1100Hz
> tone until the receiving end answers. Also, with T.38 doesn't the call have
> to come up and then T.38 gets negotiated? (I don't know, I have only read
> about it.)
> -MC
>
>>
>>
>> So, here the goal is to have a T.38 capable GW handling T.38 calls while
>> SpanDSP handling T.30...
>>
>>
>> Any chance to do that with FS?
>>
>>
>>
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