The magic of VoIP, the black magic of FoIP

The requirement

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

Most people who are somewhat technologically inclined, hate faxes with a passion. They consider e-mail to be the superior medium for complex batch 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 rather 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.

That explains the appeal of The Fax and the reason 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 pondering for potential solutions to the problem (such as internet fax services which don’t always work as advertised) I remembered that my ADSL modem router, an Intracom NetFaster IAD 1 had support for VoIP and sure enough, provided two 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?

Well, the main problems were the credibility and support of the VoIP providers. I also needed to find a company that had its datacenters in Greece, in order to minimize packet loss, latency etc. I tried a few companies before settling on – 1€ per month for the phone line and rather cheap call costs too. 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. 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 using Voice over IP protocols: 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 support it and sure enough, I managed to setup everything properly and send & receive faxes with no issues.

Then… Netfaster died; it would not turn on anymore. Actually, it randomly started resetting a few weeks ago, then it would periodically enter into some kind of bootloop requiring to be turned off and on again, then it died. My partner had a Netfaster IAD 2 (a newer version of the one I had) which also supported VoIP. True enough, after re-setting up everything, VoIP was indeed operating normally, incoming faxes were received properly but… I could no longer send any kind of fax.

What was happening was that when my fax initiated a connection, the remote machine wouldn’t recognize the handshake signal and would not connect. Worse yet, when I disabled T.38 the connection would drop instantly after the remote fax answered the call, even though I ensured I used G.711.


The solution (?)

Since these routers were only provided as part of a double-play package and the company (Hellas Online) stopped providing VoIP telephony a few years ago, it’s impossible to buy a new Netfaster IAD device. One could ask at this point: Why not buy a better router or a separate ATA adapter? Well, Netfaster IAD 2 was supposed to be better than the one I had but still didn’t work properly (despite advertising T.38 support). At this point I needed some kind of guarantee that a new VoIP router would work properly with FoIP which is impossible unless you buy a device and try it out.

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 monthly volume 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.

I found a used Netfaster IAD 1 device on an auction web site for €20 which I promptly ordered, received, configured and went out to test it. Sure enough, I now could send and receive faxes properly. My only worry is that it started doing these random resets too which would mean that this is some kind of a generalized issue with the IAD, possibly forcing me to risk purchasing a better router while hoping it has proper T.38 support.

I’d certainly like to buy a new router that has a proven performance record (such as a Fritz) but it feels like a wicked lottery for something that while remains around, is slowly dying.

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