Finally we had some bench time and got down to business. We loaded up a Patton Smartnode 4520 series gateway. In our tests we used a FXO/FXS gateway, but we then duplicated the configuration for a customer site that needed an 8 port FXS gateway configured. By making each FXS port "register" to sipx and setting up each FXS port to use t.38 bypass, we were able to make it send faxes internally by dialing the internal FAX extension of a sipxecs user. That was our first test.
Secondly we dialed a fax number to a POTS fax machine. This call went through an ITSP that provides t.38 connections (origination and termination). Magically, the fax also sent. By running a debug of the media-gateway we could ensure we saw t.38 packets flowing across the unit.
This is a nice way to transition traditional fax machines and fax lines:
- All calls go through the sipxecs system and are seen in the CDR reports.
- All plain paper devices can fax internally (by dialing the DID number or the sipx fxs registered plain paper extension or the sipx fax enxtension). These calls never leave your network.
- ANY plain paper fax machine now can act like a network black/white scanner! Cool!
- Moving the DID number from the FXS user account to the unified messaging FAX DID now changes the fax machine from incoming plain paper to "paperless". (We found this handy for a customer with a machine that broke. "Can't receive faxes till it is fixed, no problem, check your email.")
As long as you have the right gear, like a PRI/POTS gateway with t.38 support or an ITSP who DOES properly support t.38, this will always just "work".
Call flows we tested (this using the gateway in a remote office with a vpn tunnel back to our sipx server, talk about brave!):
- Direct to PSTN fax -- Works
- Direct to internal fax -- Works (all 3 types mentioned above)
- Custom dialing rule (site to site) to a sipx system across the internet (no PSTN involved) - Works
- Fax from internal plain paper fax to another plain paper fax. - Works
- Fax from plain paper fax to internal paperless fax. - Works
- Fax from PSTN to paperless fax. - Works
- Fax from PSTN to plain paper fax. - Works
What we will do is add a function in our gateway to auto prepend digits which is how we will send calls to sipx so it can identify and execute the correct dialing plan to use ONLY t.38 providers. This way NOONE has to be told differently how to dial a fax number, and all those pesky speeddial entries can remain untouched. THis is really only necessary if you have multiple gateways and dialing plans have to be created to route calls from the "fax" device to the correct gateway. It's pretty easy, but it should not be overlooked.
Focusing on the cost aspect, we "know" a t.38 provider can cost as little as 2-3 dollars per month per DID and 1-1.25 cents per page. Does this mean you should upgrade your exsting fax infrastructure? Try to determine how much you pay for your actual FAX line(s) and what the long distance associated with those might be first. Then decide how much hardware you will need and compare that against the "anticipated" costs. We realize there may not be monetary gains in giving the CEO and/or Human Resources their own fax DID to receive paperless faxes, but they might appreciate no prying eyes on their fax correspondence to get it routed to their paper tray on their desk. Did we mention paperless is "green"?