I'm familiar with Networking, VoIP, Asterisk and Linux... but I've never deployed a VoIP with PSTN.

I've got one week to deploy VoIP + 2 PSTN numbers, I don't mind reading like crazy but I would like to get a recommendation on what hardware to buy (not the specific model, but just the specific kind of hardware), like "you need a X card with Z ports" or something like that.

I guess I need some kind of FXO/FXS card connected to my server with maybe 2 ports (the numbers are going to be analog, but the phones are going to be IP).

I could buy a card and then spend my time setting it up, but of course I don't want to buy something that's just not going to work.


You're correct that you need an FXO/FXS card presuming that your phone lines will be analog. I've used cards from both Digium and Sangoma. I'd recommend sticking with the major manufacturers of these cards for Asterisk as this is your first setup and you want it as simple as possible. Digium will be a little simpler but I'm partial to Sangoma cards as we've not had any reliability issues with them.

The analog cards you can buy from the manufacturers I recommend are module so you typically start with a card that has 4 physical ports and you plug in the modules you need. Just remember that to connect your system to the pstn you're going to need "FXO" ports on the cards.

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  • I guess FXO and FXS are differentiated not just by its software functioning but also by its internal hardware, right? (because the voltage) Or a single port can work as FXO and also as FXS? – user78442 Aug 8 '11 at 1:19
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    It's actual hardware differences in these internal cards. The FXS port needs to provide voltage on the line. I've worked with other hardware that allows you to specify if a port is FXO or FXS but I've never seen that functionality in the cards. Basically you pick a card and then select which modules you want. You can mix and match FXO and FXS in a card. One thing I forgot to mention is echo cancellation. I'd strongly suggest getting a hardware echo canceller when you by the card. It's a little more money but it saves on grief later. – dkwiebe Aug 8 '11 at 1:22
  • Ok, good to know. So I should get a card with FXS too only if I were to deploy analog phones, right? With only IP phones, all-FXO card is the best way to go I guess. – user78442 Aug 8 '11 at 1:26
  • That's correct. As I mentioned, the cards I would recommend are modular. You can start out with 2 FXO ports. If you want to add more FXO ports later or even FXS ports it's as simple as adding modules. – dkwiebe Aug 8 '11 at 1:27
  • The echo cancellation feature can be added as a module later or done by software? Or is it on-board always? I'm seeing some prices on Digium Store and without EC the price drops from $451.00 to $192.50. BIG difference. – user78442 Aug 8 '11 at 1:43

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