Faxing solutions

Gabriel Gunderson gabe at gundy.org
Sat Oct 15 09:37:25 MDT 2005

On Sat, 2005-10-15 at 07:50 -0600, Hans Fugal wrote:
> Sorry for th ignorance - haven't finished reading my asterisk book yet
> - 
> but does fax not work over PRI? I know people say "don't do that"
> about fax over VOIP (although I've heard you can get it working I
> wouldn't try it in a production system), is PRI in the same boat?

There are two faxing issues with Asterisk and VoIP:

1) If you have the fax go over VoIP at some point in the call then you
will likely experience loss that may ruin the fax.  It's not like voice
where your brain can fill in the missing info.  How bad really depends
on the network connection and codecs used.  It's generally a bad idea
and something that should be avoided.  So, don't use the IP part of VoIP
(sip, iax, etc....).

2) You also need a way to get the fax that came in over a PRI or POTS
(or VoIP if you are asking for trouble) out to a modem.

You could buy another T1 card and send it out to a modem that takes a T1
instead of a POTS line.  You then have to buy 2 expensive pieces of
hardware.  Although this would probably work well (even in a super high
fax situation), it would be very expensive.

You could buy a TDM400P and add a few modules (one for each fax).  This
might be the best fit.  You can use your old fax machines.  I don't know
if that is a plus or minus.

You could buy a channel bank and another T1 card.  Then calls can get
out of your Asterisk box via your new T1 into your new channel bank.
This would have the added benefit of having a few extra ports for legacy
phones in addition to your fax.  Kinda expensive if all you really want
is a fax.

There is one last option that I've heard about, iaxmodem.  It's still
under heavy development but offers real promise.


It goes against the grain buy using VoIP and doesn't require hardware.
It works like this:

Telco --> T1 --> Asterisk --> IAX --> IAXModem --> HylaFAX

This will be pretty cool when they get it rock solid.


P.S. Still hoping for fax service suggestions.

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