[Freeswitch-users] Detecting fax on an incoming call leg (direct T.38 case)

[Roland Hänel]

one more question:

what would also solve my problem if it was possible to know about the
re-invite on the event socket (inbound) in some way - then I could switch
to rxfax without doing any tone detection at all. But it seems that there
is no way that FreeSWITCH lets me know about the re-invite...

greetings,
roland





2011/11/29 Roland Hänel <roland at haenel.me>

> I'm trying to reliably detect whether there is a fax machine on an
> incoming channel.
>
> Right now, it works nicely with the following dial plan:
>
>        answer
>        spandsp_start_fax_detect
>        sleep 5000
>        spandsp_stop_fax_detect
>        [... no fax there, so now do stuff that has nothing to do with fax
> ...]
>
> If the remote end is a PSTN fax, spandsp will fire an event upon detecting
> the CNG tone, and I will react accordingly.
>
> However, if the remove end is a T.38 fax, which will immediately re-invite
> after answer, then the following problem occurs:
>
> FreeSWITCH does not answer the re-invite (just says 100 Trying and nothing
> follows). Even though the remove end fax transmits the CNG tone afterwards,
> it is not detected by spandsp. I have recorded the call to make sure the
> CGN tone is there, and it is there. I have even played this tone into
> another phone call, where it is successfully detected by spandsp. All I can
> guess is that the non-answered re-invite might block spandsp from detecting
> the tone?
>
> Greetings,
> Roland
>
>


-- 
Gruß,
Roland
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