[Asterisk-Users] Diffrence bewteen FXO and FXS

[Max W Blackmer Jr]

Here is an excellent document explaining the differences between FXO and
FXS.
http://www.google.com/url?sa=U&start=5&q=http://www.patton.com/technotes/fxs_fxo.pdf&e=7385

Also you can look at Digium's site for their description, which
describes it from a stand point of Asterisk as the PBX.
http://www.digium.com/index.php?menu=fxsvfxo

> Why are there FXO cards, and FXS cards? What's the difference, and why
> is it needed? Modem cards, seem to be able to dial out, and receive
> calls, so why are these cards different?