Online StoreThe Facts about Faxing
For the most part I don’t really understand why FAXing through a PBX system has become such a big issue over the past couple of years. Legacy PBX platforms have never dealt with FAXes so why should an IP PBX platform be expected to perform a task that big iron systems have never tackled? Even though FAX technology is severely outdated and probably should have been replaced decades ago, it is something that we need to find solutions for since there are many legitimate and actual legal reasons why FAXing is still used today, and there is a lot of confusion about what actually works and what doesn’t.
Why is FAXing Difficult Anyway?
Most of the issues with having an IP PBX platform deal with FAXes is that there has to be a real-time Analog-to-Digital conversion going on, and on top of that, the digital side of things is completely unforgiving if there is any packet delay or loss, the entire transaction can, and usually will fail. Having a piece of software try to emulate the modem sounds while encoding/decoding the signal while doing a digital-to-analog conversion and then dealing with any switching delays from running through the PBX software and its almost a miracle it ever works at all for anyone.
This also explains why FAXing over VoIP is so unreliable. If you are on a voice call, a dropped packet here or there may not even be noticeable and thanks in a large part to cell phones, people are more tolerant of poor quality voice conversations if they occur. A FAX transmission over VoIP has no ability to resend packets (due to voice being over UDP) so if a packet is lost or out of order, it is just dropped which will cause major problems for the FAX transmission.
The Promise of T.38
Some of you have heard that T.38 is the solution to all of our FAXing problems, and theoretically, that is correct. What T.38 gives us is a true digital protocol for sending and receiving FAX transmissions. This packetized process ensure delivery of the FAX packets and essential guarantees successful transmissions. So why hasn’t this solved the FAX problem once and for all? Mostly because this would take replacing millions of FAX machines with T.38 capable devices. Since many FAX machines still being sold do not have T.38 capability, the problem isn’t going to be solved entirely by T.38 anytime soon.
What are the solutions?
There actually a handful of different ways of dealing with the FAX problem and we are going to look at the pros and cons of each one to help you determine the best options for yourself and/or your clients.
Plain Old Fax Service
Most certainly my top recommendation is to use regular FAX machines or FAX servers connected to POTS (analog) phone lines. Beyond any doubt, this is the most reliable method of sending and receiving FAXes. On the downside, you need a dedicated device or server along with an analog phone line which is going to cost you money on a monthly basis.
Incoming PRI to FXS Port
If you already have a T1 PRI circuit coming in, paying for an additional analog phone line just for FAXes is frustrating to say the least. What many people find is that this setup is highly unreliable, and most of this is due to timing issues between the FXS port and the T1 port. To solve this, you need to pass the timing signal from the PRI over to the FXS port. The only reliable way to do this today is with a Sangoma PRI card and a Sangoma A200 Analog card connected together via a timing cable. While this configuration works well, it is pretty costly to implement and the endpoint is still a traditional FAX machine.
T.38 via Gateway Devices
What is proving to be a very reliable solution is to use a gateway device for your PSTN connectivity that will recognize an inbound and convert it to T.38 so that it can be properly processed by a software PBX platform. A great combination of this setup is 3CX with it’s built-in FAX service using Patton 4960 (PRI) or 4114 (FXO) devices. While this setup assumes you are using PSTN circuits, at least you can use the gateway for both your PSTN termination as well as the T.38 conversion. These devices cost a little more than some other gateways, but they do solve the problem is this particular situation.
T.38 via SIP Trunks
Currently, very few SIP trunk providers provide T.38 signaling. If you are fortunate enough to have a SIP trunk provider that can deliver T.38, and an IP PBX platform that supports T.38 FAXes such as 3CX, then your results will be quite good.
FAX Services
The best results we have seen besides a FAX machine connected to an analog phone line is with good quality FAX services, and the best so far has been FaxxBochs. The way this service works is a small Intel Atom based system is placed on the customer premise which connects to the FaxxBochs service. An incoming FAX is actually received at the FaxxBochs data center and converted and then sent to the server at the customer premise. The server is then connected to a regular FAX machine or FAX server and delivers the FAX. Outgoing FAXes are handled in the exact opposite way with the server receiving the FAX from the FAX device, then sending it up to the FaxxBochs server before being sent out over the PSTN network to it’s final destination.
Summary
Its actually unfortunate that FAX technology hasn’t progressed as rapidly as other telecommunications technologies and the vast number of installed systems that are not up to current standards makes any progress in this area painfully slow. Some predictions go out as long as 12-15 YEARS before the bulk of the existing FAX machines are “Internet ready”. Understanding the limitations of FAXing and some best practices in how to deal with businesses that need FAX ability will go a long way to helping you deal with your clients and their requirements.
Great content this article that I will share with my resellers. I am also surprised how often fax comes up as an issue.
I’d like to mention that FaxBack has a FREE plug-in for MS Fax native to business versions of XP, Vista, and Windows 7 into a VoIP Client. This allows users to connect to a media gateway (like Patton, AudioCodes, Epygi, Cisco, and others) via SIP T.38. This uses the same IP Fax driver as our Fax Server software for organizations who need more advanced functionality.
Another important thing to note is that T.38 is only reliable when there is QOS. It is not reliable over the open internet, especially when sending multiple pages. This is discussed at length by the recent T.38 problem statement produced by the SIP Forum.
FaxBack has developed a way to transmit faxes via HTTPS which is as reliable as a POTS line, even over the open internet. This connectivity can be extended to fax machines, the MS Fax client, and even enterprise grade fax servers. You can read more here: http://www.faxback.com/aboutus/pressroom/archives/2009/AnnouncesHttpsPlatform_PR092209.aspx
Feel free to contact me with questions at mark.bradford@faxback.com
Informative article, however I can’t figure out why you didn’t even mention “HylaFAX” as a alternative PRI solution. We have large entertainment companies in the Los Angeles area that we support and they love the fact that their faxes are now emailed to them in PDF format. It’s reliable and it’s a “Green” solution as well and that scores you points in L.A. Just a thought.
Originally the article was intended to discuss FAXing issues with regards to PBXs and VoIP. But per your point, I will add that when implementing fax as described above, FAX servers such as HylaFAX are indeed a great solution and preferable to FAX machines in a lot of circumstances (especially inbound applications).
I wanna share another fact with you that OpenVox also has the timing cable for Incoming PRI to FXS Port. I’ve been using it for a couple of months and it works well. It should be an alternative to sangoma’s faxing solution.
My 80 person company also uses HylaFAX along with Iaxmodem, Asterisk and a Sangoma PRI card. It works fairly well.
I’m the asterisk admin for an enterprise size company. We use hylafax with IAXModem. After some initial debugging, we’ve been extremely satisfied with it. I highly recommend this option as it can be scaled to allow for as many modems/DID’s as needed.
This line from the article is simply not true and/or misleading depending on how you look at it…
“Legacy PBX platforms have never dealt with FAXes so why should an IP PBX platform be expected to perform a task that big iron systems have never tackled?”
Every major pbx maker nowadays has and has had for some time, the ability to handle faxing. This is typically done via d.i.d pointed to fxs ports or d.i.d directed to an integrated unified messaging system that does fax to the desktop or from the desktop or both.
Many do have them but usually only the larger systems and at a price premium. Thanks for pointing that out Pat.
I’ve never seen a real PBX (as opposed to a key system that only works with special digital phones, and other cut down pseudo-PBXes) that doesn’t allow you to plug a FAX machine, or a FAX server, into any FXS port and have good service. If the connection to the PSTN is digital, FAXing up to V.34 is OK. If the connection to the PSTN is by analogue pairs, FAXing up to V.17 is generally OK, if the analogue pairs are clean.
Huge numbers of PC FAX cards, from the likes of Dialogic, have been used to make FAX servers on the back of a PBX.
FAX, and other modem applications, aren’t much of an issue with traditional PBXes, and have been massively deployed since the 1970s, when the first digital PBXes appeared.
Steve
I have worked with systems from Mitel, Shoretel, 3Com, Avaya, and several others and none of them claim to have FAX support. The bigger issue however, is when running the FAX through an IP PBX which is what I am addressing in this article. The Digital to Analog conversion is prone to problems and small delays which will wreak havoc on the FAX transmission. Since most IP PBX systems do not handle FAXing well, and since our reseller base in primarily involved with IP PBX systems, that is who this article is targeted at.