[Asterisk-Users] FXO vs FXS question

[Rich Adamson]

> as a relative newbie I obediently ordered the recently recommended
> "Newton's Telecom Dictionary" but it did not provide the answer to one
> of my question. Perhaps one of you can do so.
> 
> 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?
> 
> Or in other words, what does an FXO to FXS converter do (I have seen
> some mention but no explanation of those)?

A box/adapter that has a FXS port must be capable of "ringing" the
attached phone, and support other supervisory functions as though it
were the controlling interface to that attached phone.

A box/adapter that has a FXO port must be capable of receiving ringing
and other types of signaling, answer that incoming call, etc. In addition,
most FXO ports are capable of sending calls to the pstn line, etc.
FXO ports have no need for a ringing generator.