New TDM-GSM Module For Asterisk

A short while ago Nir Simionovich noted an interesting new piece of hardware on his blog. It’s the embodiment of a novel approach to adding GSM based cellular trunks to an Asterisk server. As opposed to a freestanding external SIP-to-GSM gateway that I installed last year, someone has devised a new TDM-GSM module that emulates that FXO daughter card on a Digium TDM400P card. According to the companies web site two modules can be installed to a TDM400P card, providing Asterisk with two GSM trunks. No drivers are required beyond those loaded for the TDM400P.

tdm-gsm-module-for-asteriskThis approach could have some advantages. Most obviously it keeps the entire VoIP system in a single chassis, with no wiring between Asterisk and the GSM gateways. No requirement to power a second device. No dependence upon a network switch staying powered to ensure access to the gateway in emergencies.

It could also be cheaper since no case or power supply is required, although there is as yet  nothing about pricing or availability on the companies web site.

There’s also no detail given about the mechanics of the antenna. I would hope that they make provision for a chassis-mounted external antenna connector. I have the antenna from my Portech GSM gateway up high about 3 meters from the location of the device to get the best RF signal possible in my office.

My perspective is that this sort of hardware facilitates an inexpensive, open source path to fixed-to-mobile convergence (FMC) that makes a lot of sense. Using cellular trunks can provide access to SMS, provide emergency lines, as well as cut long distance costs by leveraging mobile-to-mobile minutes common to many cellular rate plans.