[asterisk-users] Fax/Modem, Asterisk, Channel Banks

Tim Nelson tnelson at rockbochs.com
Tue Aug 3 10:04:16 CDT 2010

----- "Joel Maslak" <jmaslak at antelope.net> wrote: 
> I've been replacing an old Toshiba DK switch with an Asterisk solution. I'm needing a solution for fax machines that works as well as a POTS line from my carrier. If the POTS line is the solution, I'll keep it, but I'd rather move away from that. 
> Here's what I'm thinking...will it work? 
> I would use a dual-port Digium T1 card. In one port, I'd terminate a telco PRI T1. In the other port, I'd terminate a Rhino channel bank, connected to each of my fax machines (and a stamp machine with an internal modem). 
> What I'm wanting is to be able to send/receive faxes via the telco PRI and the analog fax machines. I also want the stamp machine to work. I don't want this to work 98% as well as the Telco - they truly need to work 100% as well. 
> So...will this work? 

Be absolutely sure you have your Zaptel/DAHDI timing settings correct so all ports are sync'ed properly with one timing source. Also, ensure your telco is giving you a real TDM circuit/path, not a TDM port that is serviced by a VoIP connection. Many companies are doing this now as it cuts their costs significantly for service delivery and works fine for voice but you'll have problems galore trying to get a modem/fax carrier working reliably. They'll usually call this product a 'flex T1' or 'Mega T1' or some other marketing-hype type name and give it a lower cost. You don't want to walk away from these products, but rather, run as fast as you can. :-) 

I've used the Rhino channel banks extensively and they work very well. In fact, a recent installation was specifically for combined voice/fax/modem usage and it performed perfectly. The only difference in my case versus yours was that the T1 was being provided by the telco, not via a T1 card in another Asterisk box. But again, assuming you have your timing setup correctly, this should work very well. 

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