Incoming Fax Quit Working - No T.38

Thanks in advance for your help. I am lawyer, not a tech guy. I would be happy to pay someone $100 to spend an hour to try to this problem for me, but it isn’t worth the $400 minimum Sangoma tech support charges (I will just plug in the old fax machine before I spend $400). If you are willing to help me, just let me know.

My office PBX has the Fax Pro module installed. We have used it for years without a hitch.

However, recently all incoming faxes fail. FreePBX picks up and spends about 30-40 seconds dealing with the call - but then fails. Senders get a COM ERROR message.

Outgoing faxes still work.

Our connection is FIOS/VOIP Provider → Analog POTS Interface (provided by FIOS provider) → Grandstream GXP Analog/SIP Gateway → FreePBX machine → Fax User Extension

T.38 is not working and I don’t know if it was ever working- I never checked because faxing worked fine out of the box until now. I don’t know if there is no T.38 because my FIOS/VOIP provider doesn’t support it or if it is because I have the settings wrong in my FreePBX box. But we were getting faxes fine until about a week ago (whether over T.38 or G.711)

Here are the results of SIP SHOW STATS:

FAX Statistics:

Current Sessions: 0
Reserved Sessions: 0
Transmit Attempts: 2
Receive Attempts: 17
Completed FAXes: 17
Failed FAXes : 16

Spandsp G.711
Success : 1
Switched to T.38 : 0
Call Dropped : 2
No FAX : 0
Negotiation Failed : 0
Train Failure : 0
Retries Exceeded : 13
Protocol Error : 1
TX Protocol Error : 0
RX Protocol Error : 0
File Error : 0
Memory Error : 0
Unknown Error : 0

Spandsp T.38
Success : 0
Call Dropped : 0
No FAX : 0
Negotiation Failed : 0
Train Failure : 0
Retries Exceeded : 0
Protocol Error : 0
TX Protocol Error : 0
RX Protocol Error : 0
File Error : 0
Memory Error : 0
Unknown Error : 0

Don’t count on T.38. I’ve seen docs that say that you have to start with a normal line and then renegotiate. I’ve used a couple of the Grandstream HTxxx ATA devices myself, though I prefer the small Patton boxes. I have some fax systems that even use VPN tunnels using a G.711 codec and nothing else. Grandstream has a couple of options that allow to fine tune these things.

The problem with your kind of problem is that someone has to enable a couple of log options and then change a couple of things based on what gets printed. At the end of the day, $400 may not be that much if an engineer spends a day on that. On the other hand your setup looks a bit weird and overly complicated. I’d probably not use the POTS device but go straight into FreePBX and maybe then I’d use a simple ATA device to hookup an old-fashioned fax machine.

T38 is an ip protocol as such it can’t traverse an ATA (Analog to Telephone Adapter).
Your grandstream gateway however can handle both T30 and T38 and also voice over g711, perhaps you can register that directly with your VOIP provider for that DID.

T38 is a better option when an ip connection is involved due to it’s ability to handle missing or out of order packets if the renegotiation from T30 (g711) is successful. Even if not, then there is two less devices in the stream to not worry about and you can also attach your fax machine directly to one of it’s FXS port bypassing FreePBX’ ‘passthrough’

Thanks for your reply. The staff in my office likes the fax handling features, but we don’t get enough faxes to justify spending a lot of money to fix it. I could just dust off the fax machine and plug it in. That said, I don’t mind spending $100 to let somebody look at it for an hour to see if they can fix it (or not) but it’s not worth $400.

Thanks dicko. We have a bundled FIOS/phone service. I FIOS provider gives us 4 DID’s that go into our Grandstream Gateway and then to the PBX. One of these I have set up as a dedicating incoming route to a Fax Recipient.

Our outgoing faxes go over VOIP trunk (as do all of our outgoing calls). I think I have the T.38 settings screwed up - the T.38 stuff I found online does not match up to the new FreePBX interface.

As a practical matter, I don’t care what method the PBX uses, but given your post, maybe the easiest thing to do is just port the fax line to a reliable VOIP provider and use T.38 without worrying about an ATA or gateway… Do you have a recommendations for any reliable T.38 VOIP providers?

I have found Vitelity Flowroute Telnyx and VoipInnovations all to do T38 reliably.

Of these Flowroute is probably the easiest to set up but Telnyx the more flexible option.

Thanks again Dicko…

I would still rather pay somebody $100 to give me an hour trying to fix what I have. If I can’t find anybody, I will go down this path.

If anybody wants to give it a shot, I will PayPal the $100 in advance, with the understanding that it can’t be fixed in an hour, I will do what Dicko suggests. I wish Sangoma either (i) had a quick fix option (ii) would give more time before tech support fees expire, because I would like to help them. I used them before and they fixed my problem fine, but it was really too expensive for our small (4 person) office because all of our unused time expired. $600 to fix a problem that took them 10 minutes to fix. This is not Sangoma’s fault and they are a GREAT company providing me with a GREAT FREE PRODUCT that is crucial to my business - I just wish they had a niche tech support option in between mooching of off volunteers like Dicko and jgttgns (thanks to both!) and a $200 per hour tech support plan that is more suited to larger businesses and that just doesn’t make sense for a small office like mine that has a minor problem every blue moon.

It really isn’t directly an any way a Sangoma problem, That your provider is not able to successfully send faxes to you is their problem alone.

That your solution does not provide a T38 pathway to your PBX is neither their problem.

Corporately I use hylafax and t38modem successfully for many hundreds of fax pages a day with fax2email and email2fax with a success rate of +99% but if you only have a few I suggest you subscribe to something like for less hair pulling and only a few bucks a month.

I know it’s not a Sangoma problem… But I think they (or somebody else who knows what they’re doing) could fix it for me in a heartbeat, because it was working fine up until last week.

I think I will likely do what you recommend and sign up with Flowroute (VOIP with T.38). I will try it out for a couple of weeks and then port my fax number to VOIP if it works OK. In the interim, I will just plug the old fax machine into the POTS line.

I use VOIP (Twilio) for outbound faxes and I just checked and learned that Twilio doesn’t support T.38. so my faxes have gone out over g.729 the whole time. Checking the log, I see some retries and failures. If inbound T.38 proves to be more reliable, I will use the new VOIP service for outbound too.

Thanks so much for your help. Can I buy you a beer or two by way of appreciation?

Fixing such a problem is not within the Sangoma/FreePBX purview, it is just a ‘transport’ problem.

Much as I like a nice IPA, I suggest you send any appreciation to Ukraine relief


You are the man !!!

Come on guys, we can all do this, even if you don’t have kids.

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It could be one or the other or a combination of both. Your stats output shows no switching to T.38. The way T.38 works is the receiving side (you) tells the sender to use T.38 which will cause a reINVITE with T.38 UDPTL.

Show the settings for your trunk, let’s see if the T.38 stuff on it is correct (or even setup) and since there are a few options for error correction perhaps suggest a different one. As for your provider supporting it, that’s easy. You need to look at their documents or just ask their support. They should be able to tell you.

It is neither in this case, T38 settings will have no effect as he is connecting the trunk through an ATA.

My HT802’s support T38. My old SPAs from the 2102 to 112’s have T38 support. That’s the point of the ATA, converting the SIP to analog. Using ATAs with T38 for faxing has been done for over a decade.

And he does have a Grandstream but if you read his post the connection is through an analog output on his providers box, which of course is not SIP, and his service is ‘bundled’ so your suggestion (already suggested) is not an option here.

I was referring to HT802 <> FreePBX which would be SIP.

But that is not his T38 connectivity problem. So likely a waste of time for him.

Well isn’t good connection schema, too many voice data processing and conversion.

Digital → digital to analog(gw provider) → analog to digital (GW Grandstream ) -FreePBX …

How about to connect FreePBX direct to FIOS/VOIP Provide?

If you actually read this posting you will see that is not an option.