[asterisk-users] T.38 on a MAX/Lucent/Ascend TNT

[JR Richardson]

> Date: Thu, 24 Jun 2010 15:32:39 -0400
> From: Ben Winslow <winslowb at pa.net>
> Subject: [asterisk-users] T.38 on a MAX/Lucent/Ascend TNT
> To: asterisk-users at lists.digium.com
> Message-ID: <4C23B2D7.9090205 at pa.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> Hello folks,
> 
> I've been trying to get T.38 over SIP working with calls terminated by a
> MAX/Lucent/Ascent TNT.  As far as I can tell, SIP and T.38 are actually
> working perfectly; however, I can't get the TNT to properly terminate a
> FAX call.  Does anyone have a working configuration for SIP and T.38 for
> calls from a TNT or APX?
> 
> Here's a brief description/diagram of my test setup:
> 
> Laptop --RS232--> Modem --POTS--> Channel bank (ADIT 600) --CAS T1-->
> TNT --Ethernet/SIP--> Asterisk --SIP--> t38modem.
> 
> The TNT is running TAOS 11.0.4 with both the SIP and realtime fax
> features licensed.  I've tried using several modems, and with each I can
> establish a data call without any problems (although at a maximum of
> 31200bps/3429 baud using a 33.6 modem, for reasons I haven't dug into
> yet.)  Whenever I try to send a fax from the laptop, however, the call
> always seems to fail in the first HDLC phase (phase B) with either a
> timeout or error 23 (COMREC invalid command received.)  The modem is
> connected directly to the channel bank and the channel bank is connected
> directly to the TNT in an attempt to reduce the number of variables.
> 
> With my current configuration, the call to Asterisk will come up as a
> voice call, then be dumped into t38modem when Asterisk receives the
> 1100Hz CNG tone from the sending modem.  At that point, the call is
> dumped into t38modem which re-invites the TNT with the T.38 options, and
> the TNT usually sends a T.38 t30-ind of 0x00 (no-signal) or 0x3a (???),
> although I do occasionally see more promising messages like
> v29-7200-training or t30-data/hdlc-fcs-ok.  Shortly thereafter, the
> dialing modem will give up and terminate the call.
> 
> If I try dumping the same call into iaxmodem instead of t38modem, the
> call actually progresses further -- the real modem receives and decodes
> the HDLC CSI/DIS from iaxmodem, but the high-speed trainup always fails
> for calls coming from the TNT.
> 
> Does anyone have any advice or suggestions?  Has anyone actually made
> T.38 work with one of these devices running ANY TAOS version?
> 
> Thanks,
> --
> Ben Winslow <winslowb at pa.net>
> 

What version of Asterisk are you running?  I've struggled to get this
working as well but with TNT TOAS version 14 and Asterisk 6.1.x I managed to
get reliable T38 faxes one-way: from fax to PSTN

Fax machine><SIP T38 ATA><Asterisk><SIP T38><MAX TNT><PSTN PRI

The other way does not work, the call doesn't switch to T38 and I haven't
had time to investigate too deeply.

Fax handling in TOAS was greatly improved in 14.0 version, I would suggest
you upgrade to that if you can and start there.

JR