Difference b/w FXO and FXS

Hello All

I got two question, would be greatfull if anyone could relpy me back

  1. What is the difference between FXO and FXS…i have a small asterisk machine and i want people to make calls and receive calls from PSTN, what card should i install in asterisk FXO or FXS for both outgoing and incomming???

  2. I have implemented asterisk and we want 15 lines of PSTN,what FXO/FXS should we use that can support 10–15 PSTN lines

Any response would b e greatly appreciated

FXO would be for connecting PSTN line to asterisk
FXS would be for connecting a plian old telephone to asterisk

Digium 2400 would support 24 fxo or fxs but I have never tried it you could also use a T1 card and connect it to a channel bank to break the T1 into fxo or fxs channels
Sangoma also makes a 24 port card

voip-info.org/wiki/view/Asterisk+hardware

what is the difference between plain old telephone and PSTN???

Plain old telephone= something you would by at walmart to hook to your telephone line

pstn= public switched telephone network, this is the line coming into your house