[Asterisk-Users] FXO vs FXS question

[steve at daviesfam.org]

On Sat, 16 Oct 2004, Wolf Paul wrote:

> What is the difference in functionality between an FXO and an FXS port?
> I know that the line from telco goes into an FXO and standard POTS phone
> goes into an FXS, but since both types of ports must be able to both
> make and answer calls, what is the actual functional difference?


An Asterisk FXO interface connects to a phone line.  So it has to detect 
ringing voltage, answer (take the "phone off hook", ie loop the line) and 
so on.

An Asterisk FXS interface has to connect to a phone.  So it has to make 
ringing voltage, detect if the phone is taken off hook or put on hook, 
detect tone or pulse dialling and so on.

Steve