Faxing over ATA adapter issues - looking for an alternative


I have a Cisco SPA112 that is connected to an extension on my PBX that I am using for outbound faxing. It has been working fine for about 3 months up to this point. However lately when I try to send faxes from the fax machine, I have dial tone and it goes through the initial dialing process but I am getting Comm Errors indicating poor line quality. However, if I unplug the telephone cord from the fax machine and plug it into an analog telephone, I have dial tone and can make calls just fine.

I have tested the line with another fax machine same issues… so I’ve isolated the problem to the SPA112. I’m just a little confused because I can make calls just fine if I connect the line to an analog telephone. The SPA112 is only 4 months old or so, so if it is already failed, then that’s pretty odd.

I read about something called Faxxboch a long time ago that was supposed to be more reliable than using an ATA adapter. My problem with Faxxbochs is that it’s $30 a month… for that cost, we could just buy an analog line through the phone company to address this.

Anyone have any input on this? We are using efax for receiving faxes but would like to stick to sending faxes from the physical fax machine.


Fax over voip is 2% knowledge 98% voodoo and unicorn tears. Honestly it typically “just works” or “never will” Your best bet may be to go physical line as mentioned above or the Faxxbochs route. If all cost are truly equal it probably doesn’t matter which.

Shameless plug:
Faxxbochs is a Sangoma company which is also the corporate sponsor of FreePBX. So I would encourage this route if all cost being equal.

Thanks for the input. Considering the price of the Faxxbochs is $168 for the device plus $30 per a month, and we could probably get a phone line for the $30 a month range, while I love FreePBX and the community, that just doesn’t make financial sense.

I’m wondering if I should just replace the ATA adapter to try and fix the issue and if that doesn’t work then bite the bullet and order an analog line.


Are you using T.38 or G711?

Could it be possible your VoIP provider changed something in their infrastructure recently?

Good luck and have a nice day!


Vitelity has a LOT cheaper service …$3 a month


Or if you mainly receive faxes you may want to get a metered analog line. I think I got one years ago for about $8 a month from AT&T

I have made tests with two providers which offer T.38…

With one I was able to send reliably multiple times a 65 pages document which failed miserably with the other…

The PBX itself was the same…

There is another provider that offers something similar to Vitelity but for much less but it is currently beta and the exact price it will be out of beta is, I believe, currently unknown…

Have a nice day,


One alternative solution is to add hylafax and t38modem’s (iaxmodem if you want also) to the mix , then it becomes 2% voodoo and 98% knowledge, no matter what carrier you choose, (some are better than others :wink: ) and it is free :wink: .

Ahhh the woes of FoIP!

We have put more (fruitless) time into making it work than I would care to mention, but I can finally tell you that with the right version of Asterisk (11, 12 or 13) and the right carrier (We use/Sell BluIP - They use Broadsoft switches) and the right ATA (The ONLY 100% one I have found is the SPA-2102 with the current firmware) and T.38 and a setting “FAX T38 V29 Only” set to yes, we are getting 100% reception and sending.

Some of these requirements might not be achievable for you, and until they are all met, you WILL have the occasional failure - God, I wish FAX would DIE!

To Recap:

Asterisk 11/12/13 - Current version of any of the three.
Proivder that ACTUALLY supports T.38
Linksys SPA-2102 with Current Firmware - There are LOTS of them on E-Bay
FAX T38 V29 Only set to Yes on the SPA to limit the FAX speed to 9600 BPS.

The 9600 BPS might at first sound like a deal breaker since some of the newer FAX machines are even up to 33,600 BPS but in reality, it seems to work - even with BUSY Medical Office FAX machines - and Asterisk can receive at 14,400 BPS reliably, so that might be an option also.

I think there are a lot of us with that sentement!

The issue with T38 needs to be divided into two camps. Many provider tell you that you can send T38, but once they pass it up to their upstream providers which are usually LCRed to some level, it can fail. Even when they screen and interoperate with a provider, things change and it can fail. On SIPStation we will support T38 ‘for free’ if you want to send it up to the upstream providers and take that risk. We also provide a metered T38 option (by sending us a specific prefix) for North American phone numbers and in that scenario we ‘guarantee’ end to end T38. We do this by fully controlling your T38 transmission to our gateway where we deliver it direclty to our PRI’s. This puts us in full control of the problematic path and not at the mercy of the providers. It’s expensive (for us) but allows us to provide an optional and reasonably priced option for dependnable outgoing FAXing if our customers want to choose.

For incoming, T38 poses another problem and the choice of carrier, their level of customer service, and their technical strength and relationship with their vendors becomes much more important. There are carriers who will provide T38 for their inbound DIDs. We have that in SIPStation. However, no matter what they do to ‘guarantee’ T38, the problems are not always in their control and if FAX is critical for your business, choosing a carrier with a deep understanding and the ability to work well with upstream providers is critical. A vendor who ‘guarantees’ T38 is still at the mercy of the originating providers who hand them off calls. As such, this can lead to failed T38’s if the origianting carrier rejects requests (488) to convert the intial call to T38. Even with initial interoperability testing, things can change. When that happens, your carrier may be in a position to still guarantee you T38 but that means when they get a rejection from the originating call, they accept it as ulaw (or alaw) and then they convet it to T38 from their SBC to you. However, that can lead to partially or fully failed faxes. It’s usually better then sending it all the way to you as ulaw/alaw since it’s a shorter path, but it still has issues. In a scenario like that, you want a carrier who will investigate beyond a simple reply of “we sent you T38, faxing has issues, deal with it.” You want a carrier who is capable of investigating the full path of the call to try and determine where issues are existing so they can be addressed back at the source.

Given all of that, a provider who fully understands all of this, and is able to work with upstream providers, often 2 or more levels away, is going to save you days of grief when running into issues. It doesn’t guaratee that there will never be problems, as that’s impossible if you don’t have end to end control which no one does, but it gives you an experienced team to help you get back up and working when the problems surface as they will. It’s also why many of the FAX services available sometimes seem a bit expensive, as there is significant resources, both in backend technologies as well as manpower to keep everything functioning so that you can run your business.

If you can get away with a cheap analog line, and have no need for “PRI” type capabilities (multiple DIDs, multiple simultaenous non-blocking calls, etc.) then that is often an excllent solution and likely the recommended one. However, there are often other important factors as well as a desire to have an eFax component of the service in conjunction with a real fax machine attached.

As has been previously “plugged” by James above, we (Sangoma) have some specialized FAX techology through the FaxxBochs technology aquistion made earlier this year. Keep your eye on SIPStation though as very shortly we’ll be introducing that technology within the SIPStation product and we’ll be providing pricing options that address the ‘lower capacity’ side of the spectrum to address the need of reliable FAX for the occasional faxing needs.

Good to know and I will definitely be looking for new solutions always - I bet I have wasted conservatively 400 hours over the last 11 years we have been doing Asterisk systems futzing with FAX.

When we first started, most of our base was TDM PRI’s (not the faked IP PRI’s) and we were using Sangoma and Digium FXS Cards for the Analog connections and it worked perfectly.

Then came VoIP, and literally up until late last year, we were putting FAX machines on Analog lines because we just couldn’t make it work - finally we can, but I live in fear of an Asterisk update or a provider change that breaks it again.

Thanks for all the hard work by the way - FreePBX is fantastic and miles ahead of where it was when I started using it in 2004.

Hello Kenny,

I wish to comment upon your post, as we have considerable recent headaches and experience in resolving Fax issues using the SPA112.

We completed a large campus PBX earlier this year with complex networking and deployed many SPA112 using T.38. Whilst the site was connected in a dedicated multiple layer 2 VLAN inter-building fibre connected network with QoS, we experienced lots of issues that we could not explain using the Cisco SPA, whilst the Snom phones worked perfectly and reported no packet or jitter issues. The site used a Digium G100 PRI gateway and a Schmoozecom PBX. We did a lot of tuning work and ‘fixed’ the SPA112 to work correctly in T.38 through pure trial and error. The Cisco documentation is very poor and the behavior of the SPA112 varies between firmware versions and we had all the same sorts of issues like you have discovered that were not explainable.

May I strongly recommend that you purchase the Commercial End Point Manager module license for your PBX. Immediately you will obtain access to all the R&D conducted by us and shared back to the Schmoozecom team, which they replicated and now officially support. The benefits is that your SPA112 will just end up working as expected in nearly all situations.

Please drop a note if you end up been successful in resolving your issues.




Perhaps you miss the point that @plindheimer is making, you use a PRI, that will relieve you of most problems with FOIP, T38 can’t go across it, it will always be T30 to the terminating fax machine , so if you have a well controlled network between your network placed fax machines, of any type, and your PSTN PRI gateway, of course it should work, the OP doesn’t have that luxury

Hi dicko

Even with PRI gateway we had problems. We had been using PRI on a digium card with just ALAW as the early version of asterisk didn’t support t38. It worked 80% of the time on the 1st attempt. The upgrade included the G100 gateway that allowed t38 implementation. Sadely it was more complicated than expected, thus my previous comments.

My experience with Fax Over IP is that a good quality ATA makes all the difference and is much more important than whether you use T.38 or uLaw. If the ATA isn’t capable of converting the analog fax signal to digital and preserve all the detail, the fax won’t work no matter what else you do. I have found that the Cisco and Grandstream single-device ATAs are terrible at converting analog to digital in a way that allows fax to work. The Grandstream ATAs have a noticeable overdeviation and makes normal voice sound distorted, even when you turn the transmit gain all the way down (it just sounds quieter, but still distorted).

The Obi ATAs (Obi 110 or 200/etc) do the conversion very well. I’ve had zero problems faxing over IP when using them, even with uLaw. If you want to continue using your fax machine, I highly recommend them.

I haven’t tested the multi-port grandstream ATAs, but they cost considerably more and so I’d expect them to have better analog to digital encoders, but that’s just a guess. I believe Obi also makes multi-port converters and I’d expect them to be just as good as their single-port devices…

Hi AdHominem

Did you have to configure any special settings on the Obi’s for them to work with FoIP correctly or did they just work out of the box? Also I am mainly concerned with sending faxes, we receive via fax to email.

I am thinking about trying your solution first, then moving over to Vitelity Fax Enable if I can’t get it working.