[asterisk-users] How to enable T.38 between SPA3102 PSTN Line port and ReceiveFAX app ?

Larry Moore lmoore at omninet.net.au
Tue Nov 5 16:23:23 CST 2013

On 5/11/2013 6:09 PM, Olivier wrote:
> Hello,
> I've got an analog phone which is currently receiving unsollicited FAX
> calls from PSTN.
> For learning purpose, I'm preparing an Asterisk/SPA3102 setup that would
> let voice calls come in and out and translate incoming FAX calls to TIF
> files (forwarded through email)).
> My target setup is :
> PSTN <-- analog--> SPA3102 Line Port <-- SIP --> Asterisk <-- SIP -->
> SPA3102 Phone Port <-- analog --> Analog phone
> When a call comes in, analog phone rings.
> If callee answers and a fax tone is detected, then the incoming call is
> sent by Asterisk to ReceiveFAX application which translates incoming
> audio to TIF file.
> My setup is working ok when I'm using ReceiveFAX in fallback mode (with
> f option).
> Then I would like to improve my setup letting ReceiveFAX negociate T.38
> with SPA3102.
> The trouble is SPA3102, as I configured it, seems to refuse T.38
> negociation as I'm reading lines like this in Asterisk logs:
>    == Using UDPTL CoS mark 5
> [2013-11-05 10:36:50] WARNING[3061][C-00000007]: res_fax.c:1698
> receivefax_t38_init: channel 'SIP/myline-0000000e' refused to negotiate T.38
> My question is:
> Any hint on how to configure SPA3102 PSTN Line port so that it  would
> accept to upgrade to T.38 ?

The SPA3102 only supports T.38 on the FXS port, the FXO port uses G711 
for a fax session.

The Grandstream HT503 supports T.38 on both the FXO and FXS ports.

What problem do you have receiving a fax over G711?


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