March 19th, 2008
The cheapest way to do VoIP is still analog
What happens when you want to just want a bunch of phones in your business, hotel, or organization and you don’t need a bunch of fancy and complicated features on the phone? It’s simple, just get a bunch of cheap analog phones. But how do you build a phone system to support a bunch of analog phones? It’s simple, just get a PBX (Private Branch Exchange) with a few FXS interfaces to plug in the phones. Just to rehash what an FXO and FXS phone port is and what the differences are, here’s a text representation how these devices are connected:
- Phone (FXO) - (FXS) Channel bank (FXO) - (FXS) Telco
- Phone (FXO) - (FXS) Telco
But this is where the tricky part comes in since your typical IP PBX which is essentially a computer doesn’t have any FXS interfaces so that’s where channel banks come in. A channel bank traditionally converts a T1 PRI interface in to 24 separate channels for 24 phone lines. The problem with traditional channel bank is not that they’re all that expensive, but the fact that they require a T1 PRI interface on the PBX for every 24 phone lines which are very expensive and cumbersome.
To get around this problem of having to use expensive T1 cards that are tied to a single server, Xorcom shuns T1 cards and uses good old USB 2.0 for its interface to the PC. Pictured below are some Astribank products with FXO or FXS ports along with the option for PRI ports. You just plug in your TBX to one of the Astribanks via one of the abundant USB 2.0 ports and you’re done. Simply plug it in to a USB 2.0 switch and two cheap open-source PBX appliances and you can instantly flip between the two servers in case one of them goes down for whatever reason. Any problems with one PBX server and you simply need to flip the USB switch and the other PBX is instantly lit up with all of its FXO and FXS ports. Trying to swap a PCI card with a T1 interface is far more difficult.
Pictured above is the front view of three Xorcom Astribank models ranging from 8 to 32 ports with any mixture of FXO and FXS ports. Pictured below is the back of the units showing the power and USB port in the back. The larger models also have 50 pin breakout ports so you can use your existing breakout box if you chose to do it that way.
The next two photos show all-in-one appliances designed to run Asterisk or Asterisk distributions from popular vendors like Trixbox or some other Asterisk derivative.
George Ou is Technical Director of ZDNet. See his full profile and disclosure of his industry affiliations.
