Fax over IP is a pain

The requirement

A few months ago came the need for a fax machine. Worse yet, it had tobe connected on a dedicated phone line since the main line was configured to redirect unanswered calls to a mobile number after a number of rings, while incoming faxes could occur any time of the day.

Most people somewhat technologically inclined, hate faxes with a passion. They consider e-mail to be the superior medium for non-vocal communication and regard fax as a relic from the past that refuses to die. While I sympathise with them I can also understand the appeal of The Fax for certain people; it’s easy to feed a document to your device, dial in a number and be done with it, rather than learn how to use a computer, a scanner and an e-mail app. Well, doubly true if you are an older generation!

That explains why it’s still in wide use today (at least in Greece, where basic computer knowledge such as sending a scanned image as an e-mail attachment is surprisingly hard to find). In any case, while a dedicated phone line for the fax was deemed a necessity, it still wouldn’t justify a price of €15/month. What could I do, really?

While considering options (such as internet fax services which don’t always work as advertised) I remembered that my ADSL modem router had support for VoIP and provide a couple of RJ-11 ports. Could I perhaps buy a cheap VoIP account somewhere and connect my multifunction printer (which doubled as a fax too) on it?

I tried a few companies before settling on viva.gr – 1€ per month for the phone line and rather low tariffs sealed the deal. I bought an account, configured my router, made a few VoIP calls and everything worked nicely.

It was there I found out about the T.38 protocol. You see, the main problem of the fax protocol (T.30) is that it doesn’t really tolerate any kind of packet loss, like not at all. When you use a normal land line to perform a fax transmission, packets are guaranteed to be transmitted in order. VoIP telephony though, provides no such guarantee (the IP part in VoIP) and while you can handle a few packets being out of order or even lost in the way with voice calls (you’d probably not even notice) that’s a no-no for fax communication.

There’s another thing about Fax over IP that matters: The codec. Most VoIP providers support a G.729 codec that (rather ingeniously) compresses your voice down to 6.4Kbit/s (or more commonly, 8Kbit/s) while retaining acceptable voice quality. Considering that most faxes usually operate at a speed of 9.6Kbps, 14.4Kbps or even 33.6Kbps, it would take a miracle to transfer anything using that codec (since it’s both bandwidth limited and lossly compressed).

A partial solution to this problem, is to use the PCM-A/U codec (also known as G.711 and μ/a-Law) which incidentally is the same protocol ISDN uses for voice, at 64Kbps. This alleviates the problem a bit, and allows rather reliable transmission with speeds of up to 14.4Kbps (the most common recommendation is 9.6Kbps though) but it’s still somewhat fragile since it’s susceptible to packet reordering & loss. T.38 combats this using hacks, like requiring partial retransmissions or padding messages in order to achieve acceptable timing.

The problem

As I mentioned, T.38 solves this problem but has to be supported on both ends, that is, the modem and the provider. Fortunately both my netfaster and viva.gr support it and sure enough, I managed to setup everything properly and send & receive faxes with no issues.

Then… my modem/router died; it would not turn on anymore. I tried with another one of the same company (they were provided freely by my ISP) but that didn’t last long either.

The solution (?)

Since these routers were only provided as part of a double-play package and the ISP stopped providing VoIP telephony a few years ago, I had to look elsewhere.

A separate ATA adapter would need to support FoIP (that excludes the lower end models) but still wouldn’t offer any guarantee of proper T.38 support. Plus, both a router and an ATA adapter could turn out expensive; even 50€ would not be worth it for a dedicated fax line (I remind you that while fax was a requirement by no means the expected monthly usage would justify such a cost). Thing is, I woulnd’t mind paying even €100 for a new router/ATA device, had I any kind of a guarantee that FoIP would work properly – a guarantee that was impossible to have.

In the end I bought a Fritz modem/router that supported FoIP, but I eventually managed to stop using fax, instead insisting on e-mail or even regular mail, and I couldn’t be happier.

Leave a Reply

Your email address will not be published. Required fields are marked *