VoIP Faxing with the Sangoma Fax Sync Cable

August 24, 2009 by Garrett Smith

Looking for a reliable VoIP Fax Solution?

Wait no longer. The Sangoma Fax Sync Cable can help.

All of you VoIP engineers, installers and end users have heard it, “Keep your faxing off of your VoIP system

And for good reasons. Fax over IP historically works about 50% of the time, leaving most users scratching their heads as to why.

Let’s put it this way, when someone sends an email and the packets are interrupted, say one or two drop out, the email recipient simply sends a request to the sender, asking for the lost packets, the sender sends those packets again, the recipient re-arranges them and you have your email.

With VoIP on a SIP call, if packet loss occurs, the users may hear a bit of broken silence on the line for short periods of time, simply because voice traffic is considered “real time”. With faxing, if packet loss occurs, since fax machines are considered “dumb terminals” in the VoIP world, many times the fax never even makes it to the fax machine with no alert or notification, or the fax machine displays an error instead of the fax.

For companies conducting their main portion of their business over faxing, this is unacceptable. For health care applications where faxes may be considered “mission critical”, this may be detrimental to a patient’s health.

As you can see there are plenty of applications that are using VoIP and trying to successfully integrate their fax machines into their VoIP system and make it work every time. Sangoma technologies have designed a Sangoma Fax Sync Cable to do just that. Sangoma states that their “Faxing solution works 99 % of the time.”

To start, you’ll need a few items:

  • IP PBX Server (Phonebochs, trixbox, Asterisk, ect…)
  • Sangoma Digital PCI card. You can use the A101, 102, 104, 108 and so on and so forth. Or if need be, you can use BRI or any other form of Digital communication. (It is HIGHLY recommended to use echo cancellation on this card)
  • Sangoma Analog PCI card. You can use any of the combination’s of FXS/ FXO cards you wish (A200 or A400 Series), but you must have at least 1 FXS Mod (2 ports total) to hook up to the fax machine. (It is not required, but still recommended to get echo cancellation on this card)
  • The latest version of Drivers for the Analog and Digital PCI cards. (Trixbox and Phonebochs already have these.)

Here’s how it works:

  • Faxes coming into a VoIP PBX system over T1 PRI lines are taken in by a Sangoma A101D (Single T1 PCI card with echo cancellation).
  • Also included with the VoIP PBX is a Sangoma A200 (RJ-11) or A400 (DB-25 which may require a breakout box and the use of a Sangoma Y cable) series FXS card. This card is where you will physically connect your analog fax machines into.
  • Lastly, connect the Sangoma Fax Sync cable from the A101D T1 card to the Sangoma A200/A400 FXS card via each card’s jumper connections. This cable needs no additional configuration and simply put by Sangoma,“All T1/E1 & BRI cards supporting this feature will automatically provide the clock, and therefore no additional configuration is necessary.


  • If the fax comes in to through a voice T1 and gets handed off to an analog card, where does the VoIP come in?

  • Chris


    The solution consists of a T1 Sangoma card and FXS Sangoma card installed into a VoIP IP PBX. The PBX and asterisk based software running on the PBX simply passes-through the fax from the PRI to the analog card. This pass through is done at a 99 percent success rate because the sync cable is clocking the timing from the PRI to analog card. You could also perform this solution with , lets say a Linksys spa-2102 (suggested for faxing), but the success rate of faxing is cut in half. This is the most simplistic form of intergrating a fax machine with a VoIP solution.

    Hope this helps.

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