[asterisk-users] T.38 negotiation error

[David Backeberg]

2011/2/3 Marcello Colucci (SIRIO Informatica s.a.s.)
<MColucci at sirioinformatica.it>:
> Hi, I have asterisk 1.6.2.6 on a Debian Lenny system.
> When I try to send a fax in T.38 mode I receive this error
>
> ERROR[15035]: res_fax.c:795 set_fax_t38_caps: channel
> 'SIP/eutelia-sirio-out-00000000' is in an unsupported T.38 negotiation
> state, cannot continue.
>
> In my sip.config general section I have added this lines
> t38pt_udptl=yes
> t38pt_rtp=no
> t38pt_tcp=no
>
> If I comment this lines, the fax is sended by G711 but this modality is too
> slow and instable.

It depends on who you're faxing with.

If you can control who you'll be T38-ing with, you might be able to
solve this particular problem.

But if you're T.38-ing with the whole world, in my opinion, there are
too many broken T.38 implementations for you to depend on this.

If you want reliable faxing, you should avoid voip altogether, and use a modem.

I've gotten pretty good faxing by using audio passthrough, over sip,
but it's only sip on a LAN, to a PRI gateway system. Trying to do voip
fax over internet is cheap, but it's not reliable.