[Asterisk-Users] FXO vs FXS question

[Steve Underwood]

Andres Tello Abrego wrote:

> The way I explain the difference between fxo and fxs, is electrically...
>
> The telco lines, PROVIDES voltage and current to makes the telephone 
> ring, so the FXO is a device, adapted to recive this voltage an current.
>
> The phone, NEEDS voltage and current, to ring, so the FXS is a device, 
> adapted to provide this voltage and current.
>
> So, if you plug an FXS to a Telco Line, both equiments PROVIDE voltage 
> and current, so... what you have? Sparks and a short cut, and at least 
> like 75usd of the fxs module or even worst, like 100usd for iaxy or 
> fxs card :(

When I designed line cards for the PSTN we specifically tested that this 
sort of thing would not happen. Phone lines are handled in a pretty 
sloppy way. If a line card in an exchange blew up every time someone 
shorted two lines together they would be replacing cards all day.

Regards,
Steve