[asterisk-users] T.38 gateway ATA

Sylvain Rochet gradator at gradator.net
Tue Sep 25 10:34:13 CDT 2012

Hi Jeff,

On Tue, Sep 25, 2012 at 10:11:27AM -0500, Jeff LaCoursiere wrote:
> Aha!  That is what I am looking for.  What firmware rev are you
> using on the 3102?

5.1.12 on SPA8000, 5.1.10(GW) on SPA3102, there is probably new releases 
from Cisco, at the time I builded the T.38 network those were the latest 

Here is my SPA3102 configuration that I changed or are relevant to FAX/T.38:

Network Jitter Level: very high
Jitter Buffer Adjustment: disable
Call Waiting Serv: no
Three Way Conf Serv: no
Echo Canc Enable: no
Echo Canc Adapt Enable: no
Echo Supp Enable: no
FAX CED Detect Enable: yes
FAX CNG Detect Enable: yes
FAX Passthru Codec: G711a
FAX Codec Symmetric: yes
FAX Passthru Method: NSE
DTMF Tx Mode: Normal
FAX Process NSE: yes
FAX Disable ECAN: yes
FAX Enable T38: yes
FAX Tone Detect Mode: caller or callee

Note that my Asterisk is also configured to do Fax Tone Detect and ask 
my ATA to switch to T.38 before my ATA ask Asterisk to do so, thereforce 
I don't know if ATA Fax Tone Detection work correctly.

> So if I am parsing you correctly, the asterisk server the ATA is 
> registered to is *also* a T.38 gateway, as you have directly connected 

Yes, this is also a T.38 gateway, my goal was to use T.38 from my ATA to 
Asterisk over my non-isochronous IP network. T.38 gateway is supported 
since Asterisk >= 10 and you don't need it since you are doing T.38 
passthru, but you need a device somewhere on the path able to detect the 
FAX preamble and ask to switch the data channel from ulaw/alaw to T.38.

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