T.38 and the VoIP fax stigma

There are a lot of misconceptions about VoIP fax out there, in particular about T.38 fax protocol. Typical generalizations include “VoIP Fax is unreliable” or “T.38 doesn’t work”. Although these statements can be true when referring to a particular solution or network, they are not accurate statements in general. We would like to help unravel some of these misconceptions and explain the reason for their existence.

Back when fax was cool

As you know, fax has been around for quite some time. 20 years ago it was a universally accepted and used technology. It seemed every office had a fax machine and one of the great things about fax was its global acceptance and reach. This was due to the T.30 protocol, which allowed for transmittal of faxes over the PSTN (public switched telephone network). Over time, T.30 was optimized to deal with inherent problems of analog phone lines such as background noise and interference. As fax machine technology improved, so did the ability to handle these problems.

Then along came VoIP technology. Due to the quick rise of the internet, along with nonstop improvements in speed and bandwidth, VoIP technology is seeing mass adoption by both businesses and residences as the go to solution for voice transmission.

Lost in the mix is fax. Fax is still widely considered to be the most secure way to transmit important documents. The problem is T.30 was not designed to work over IP networks.

Enter T.38

T.38 protocol is the ITU (International Telecommunication Union) recommendation for real time transmission of faxes over IP networks (Fax over IP). It was designed to allow fax to work over VoIP networks. It works by allowing raw data transport (packetized) which IP networks are built for vs real-time audio streaming which is done over the PSTN.

In theory, T.38 is a good solution for those looking to move faxing from POTS lines to an IP network. In practice though, there have been quite a few challenges with adoption of T.38.

Some of the main problems include:

Jitter - VoIP carriers have built their telephony infrastructures to support voice call quality over internet networks. VoIP calls typically use UDP which is a streaming protocol that does not have inherent packet loss correction and is susceptible to jitter. These brief interruptions can be made up for by a human listener but can cause fax failure.

ECM - ECM or Error Correction Mode was built to reduce the number of errors in fax transmissions. Both the sending and receiving sides compare notes at the at the end of each page to check for missing data. If anything is corrupt or missing, the receiving side asks the sending side to resend just the missing/corrupt data. ECM has played a big role in improving the reliability of fax. However, it is often not used in T.38 implementations, which can contribute to image degradation and call failure.

Too many variables - Unlike T.30, which was synonymous with fax pre-internet, T.38 has not been universally adopted. There are several reasons for this. First, not everyone has moved from analog phone lines or fax machines yet. So calls are still going out over the PSTN. When everyone is on the same technology, it’s easier to identify and fix problems. Secondly, many people have turned to using G.711 to send faxes over IP. G.711 uses Pulse Code Modulation of voice frequencies. Its essentially an extension of T.30 in that it uses real time audio streaming. It is not optimized for fax and therefore faces its own set of issues. This all adds up to many moving parts and less predictability when trying to implement a reliable, IP-based fax solution. Calls are going out a number of different ways, hitting different gateways, at different speeds, and are sometimes being converted mid-call multiple times as they traverse the IP telephony backbone.

How we solve problem

I often talk to people looking for a reliable fax solution or trying to figure out why their current solution doesn’t work. Naturally, I often hear the skepticism or hesitancy in their voice. Who can blame them? Fax over IP has gotten a bad rap, in particular T.38. This post isn’t to convince you that T.38 is in fact a flawless protocol. We are merely trying to explain why it has a bad reputation. The reality is, there is no magical formula to fix all fax issues. Most VoIP carriers optimize their networks for voice traffic. Which makes sense considering voice is usually 85%+ of their call volume. Same goes for most gateways. Many have T.38 support, but most are not built for fax. So how do we get it to work?

We are specialized - Voice and fax don’t mix. At least not anymore. When every phone call was made over the PSTN, all you needed was a fax machine. But today’s telecommunication networks are quite different. Different networks are built on varying technologies and an infinite combination of hardware infrastructures. All the measures put in place to protect the integrity of voice calls act as minefields for fax calls. All of our infrastructure components are built specifically for fax and fax alone. We don’t do any voice. This means our servers, gateways, switches, routes, and other components are all optimized to make fax work.

We are not protocol-dependent - I bet you thought this post was going to end with us telling you that T.38 is the best thing since sliced bread. Sorry to disappoint. Because of the variability in network environments, you cannot maximize reliability using a single fax protocol. We have a custom cloud architecture that supports multiple protocols, document formats, and transmission speeds. Adaptability is key in modern fax deployments. Unfortunately, this is not easy to replicate.

We are not carrier-dependent - We have carrier interconnects with several tier 1 carriers throughout North America. This allows us maximum flexibility in call routing. We thoroughly test every relationship to determine reliability. We leverage our volume relationships to get premium call routing and customized features. We use a proprietary routing algorithm to determine the best way to route faxes to achieve maximum reliability. You can have an excellent software solution that quickly falls apart by partnering with the wrong carrier.

The above is just a small part of what we do. We’ve put a lot of time, research, and investment to build what we believe to be the most reliable cloud fax solution available. Our goal is to provide a real solution for companies interested in migrating to the cloud without sacrificing reliability or features. We offer affordable pricing combined with a modern, customer-centric approach.

Till next time... ;)