[asterisk-users] T.38 gateway ATA

Jeff LaCoursiere jeff at sunfone.com
Tue Sep 25 10:34:49 CDT 2012

On 09/25/2012 10:29 AM, Bryant Zimmerman wrote:
> ------------------------------------------------------------------------
> *From*: "Jeff LaCoursiere" <jeff at sunfone.com>
> *Sent*: Tuesday, September 25, 2012 11:05 AM
> *To*: asterisk-users at lists.digium.com
> *Subject*: Re: [asterisk-users] T.38 gateway ATA
> On 09/25/2012 09:26 AM, Bryant Zimmerman wrote:
>> Jeff
>> Can you please clarify your layout? If you have an asterisk 1.8 (I 
>> would use 10 for this if possible) server why can't you just take the 
>> gateway call on that via a sip trunk. If you are coming in from and 
>> land line and want to do t.38 to the asterisk 1.8 server you would 
>> need a FXO t.38 gateway. Based on your description I am not sure what 
>> your sources are and what your final desired destination is. Please 
>> be specific with your response.  We do t.38 all the time and have 
>> great success with it but the success is in the setup and control of 
>> the endpoints (gateways and ATAs)
>> Thanks
>> Bryant Zimmerman (ZK Tech Inc.)
>> 616-855-1030 Ext. 2003
>> ------------------------------------------------------------------------
>> *From*: "Jeff LaCoursiere" <jeff at sunfone.com>
>> *Sent*: Monday, September 24, 2012 9:20 PM
>> *To*: "Asterisk Users Mailing List - Non-Commercial Discussion" 
>> <asterisk-users at lists.digium.com>
>> *Subject*: [asterisk-users] T.38 gateway ATA
>> Hoping for some clarification. I would like to setup a NORMAL (not
>> T.38) fax machine on an ATA, and have the ATA be a T.38 gateway to a
>> remote asterisk (1.8) server, which is doing T.38 relay (passthru) to a
>> provider.
>> Some amount of googling today seems to imply that most ATAs are just
>> T.38 passthru devices, and expect a T.38 capable fax machine, otherwise
>> just fallback to ulaw (and mostly fail, in my experience so far).
>> So does anyone use an ATA that actually does the gateway transcoding to
>> a normal fax machine? Or am I barking up the wrong tree?
>> Thanks!
>> j
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> Hi Bryan,
> To follow an inbound fax call, our intended setup would be:
> Our upstream sends a T.38 call to our border asterisk (1.8) server, 
> which creates another T.38 call to the customer's hosted asterisk 
> (1.8) instance, which creates another T.38 call to the ATA, which is 
> over the Internet to their location.  The ATA would do the transcoding 
> (is that even the appropriate term in this case?) to T.30, to the FXS 
> connected normal fax machine.
> Its that last bit that I am having trouble confirming is a feature of 
> any mainstream ATA.  When I dug into it yesterday it seems that the 
> mainstream ATAs will passthru T.38, expecting the connected fax 
> machine to work with T.38 natively.  I can't depend on that.  The 
> asterisk servers are all remote, and though I could presumably do the 
> gateway on the asterisk server I would then have a ulaw fax call over 
> the internet to the ATA, which in my experience has not been very 
> reliable.
> Of course I will need outbound faxing to follow the reverse path, 
> letting the ATA turn the T.30 outbound fax call into T.38, which 
> travels through our various asterisk servers to the upstream provider...
> So in a nutshell, is there anyone using an ATA as the *gateway* rather 
> than passthru?  I feel I am still not being clear... does that help?
> Thanks,
> j
> Jeff
> In your call stream you must make sure that all asterisk systems have 
> the proper configurations for T.38 and that spandsp is loaded on the 
> systems. Each peer entry must have the correct setup and the correct 
> rtp port ranges must be set on all asterisk servers. Each server must 
> have the correct configurations for their firewalls as well. I would 
> flatten this to start. If possible connect the ATA's directly as a 
> registration to your proxy. You will likely have better results. We 
> have had the best luck with ATA's from audio codes and grandstream 
> currently the HT-701, 702 have been working well. You must get the mix 
> right and them keep it flat. Every time you allow user to drop an 
> asterisk box between you and the ata you will give yourself a greater 
> issues as they must become an asterisk t.38 expert to get the 
> deployment to work or you must take it on. Hope this helps.  T.38 
> works well when you get the right mix and control it.
> Bryant

Hmm, I would think I would need spandsp only if the asterisk server(s) 
would be gateways... is that not the case?  If all I want the asterisk 
servers to do is passthru T.38, I assumed nothing was needed other than 
asterisk.  Our asterisk servers are all SIP - we have no TDM connectivity.

Still interested to know if your ATAs are being used as T.38 gateways?  
It sounds to me like you are just using ulaw calls to your ATAs.  True?


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