[Asterisk-Dev] FAX Subsystem discussion.

[Steven Critchfield]

On Thu, 2003-04-17 at 09:58, John Harragin wrote:
> I have been thinking about the issues regarding transmitting faxs over VoIP
> asterisk networks. I have a couple of ideas I want to toss around with you
> guys. What I currently have in mind is fax client & server applications.
> These would basically be the same but the server would be a tdm gateway -
> where the faxes transmitted and received are handed off to the telco.
> 
> The fax client would send and receive documents to local devices (fax
> machines, network printers, email, PCs, etc. - but only the fax machines are
> really necessary, as the server could do everything else) outgoing documents
> would be queued until the entire document is received. The queued file would
> then be sent to the server app where it would be transmitted out the tdm
> gateway. Incoming documents would work in a similar manor.
> 
> This strategy would be simpler than trying to get iax, echocans and delays
> to work smoothly with fax traffic. Additionally, the image quality would be
> better and the negotiated transmission rates would be maximized.
> 
> We could probably find an existing fax server or rendering library, to
> incorporate into the asterisk app, to do most of the work. It would have to
> be lightweight so it didn't bog down the asterisk program. Would the use of
> gpl code be OK for apps? A bit of notification code would need to be written
> in addition to the app interface.
> 
> Tips, suggestions, criticism or info on fax applications that would be
> suitable for this purpose?

The problem here wouldn't be so much a fax application problem, You
could easily wrap hylafax up and make it do what you want. The problem
is that the gateways here need fax modems since there isn't( to my
knowledge) a fax modem available in software that we could use on the
end of just a TDM audio feed to code/decode with. I would also point out
that it would probably end up taking quite a bit of processor load to do
a fax modem bank in software. 

I have been somewhat tempted to try and get my hands on one of those
modem cards that has a T1 interface to hook into our T400P here and be
able to terminate faxs and backup data connections into it. Of course
once we get our PRI in, I look forward to trying to get our ISDN backup
connection routed into the PRI.
-- 
Steven Critchfield  <critch at basesys.com>