[Asterisk-Users] Diffrence bewteen FXO and FXS

[Shaoul Jacobson - TELLINK]

Hi,

First, do forgive any syntax or language errors as English is not my mother
tongue.

To make a 'long' story short, 
- let's look at a phone home.
The public switch (the very big machine at your telco) provides power to the
line. This power gives energy to your phone.
This is how a 'standard' phone can work without external power adaptor.

So, the public switch sends power, the private phone receives power

- lets look at a small office
there is a pbx (private box)
it is connected to the public phone line(s)
it receives power on those lines from the public switch
(also it will use the 110-240V power lines for real power)

it is connected to several insides phones.
It provides power to those inside phones like the public switch does.



So, some interfaces receive power, others send power.
You can also think as male and female plug.
You plug the male with a female
Likewise, you connect a fxo to fxs.
'Fxo to fxo' or 'fxs to fxs' will not work and in one case even bring
problem as the two are sending power.
The public switch is most of the time rather protected against most things,
but your card not always. So you can send some circuit to silicon heaven.

Some googling will provide similar (or better) explanations

Shaoul Jacobson
Senior VoIP Consultant
Tellink
Tel :	+32 3 201 96 36
Fax : 	+32 3 227 09 81
e-mail	shaoul at tellink.com


-----Original Message-----
From: Mr AG!! [mailto:angelisonline at gmail.com] 
Sent: lundi 2 mai 2005 11:12
To: asterisk-users at lists.digium.com
Subject: [Asterisk-Users] Diffrence bewteen FXO and FXS

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?

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