T.38 Gateway ATA

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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

15 thoughts on - T.38 Gateway ATA

  • Hi Jeff,

    I am using Cisco SPA-8000 and Cisco SPA-3102 as POTS(analog)<>T.38
    gateway to an Asterisk 10 doing T.38<>RNIS gateway and it works fine (at least better than ulaw/alaw over the whole IP network).

    However I had to upgrade all ATA firmwares in order to get something working correctly.

    Sylvain

  • 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

    ————————————–

  • 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

  • Aha! That is what I am looking for. What firmware rev are you using on the 3102? 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 ISDN?

    Cheers,

    j

  • Hi Jeff,

    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 releases.

    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.

    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.

    Sylvain

  • 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?

    Thanks,

    j

  • Thanks for the info Sylvain, that is just what I was looking for. Hoping to find that a lower model has the same feature set (don’t really need the FXO port)… I am playing with an SPA122 right now, which seems to have the same options available you mention above. I’ll load the latest firmware and report my experiences for posterity.

    Cheers,

    j

  • Had a chat with their support – apparently the OBI202 supports “T.38 Fax Relay”, which is (I learned today) the term for the functionality I am looking for. The lower models do NOT support this, only passthru.
    Sadly the OBI202 is kind of pricy. And has an odd USB port… what would that be useful for I wonder?

    Cheers,

    j

  • Jeff

    The grandstream units support both Relay and passthru depending on how you set them up.

    Thanks

    Bryant Zimmerman (ZK Tech Inc.)
    616-855-1030 Ext. 2003

  • Right –

    So here is a summary so far:

    Definitely supports “T.38 Fax Relay” to normal fax machines: OBI202, Cisco SPA8000, Cisco SPA 3102, Grandstream HT-701

    There may be more. I’m personally testing Cisco SPA122 with fingers crossed. Hoping this information gets properly indexed, as I had a !@#@
    of a time finding anything like this list myself.

    Cheers,

    j