User manual

Chapter 4
FXS and FXO Explained
Identification
There are multiple standard configurations in which an 800 Series card
may be purchased. Each configuration consists of one to four FXS and/or
FXO modules. These modules are identified by their color.
 FXS - Foreign Exchange Station (Green Modules)
 FXO - Foreign Exchange Office (Red Modules)
This chapter provides an in-depth review of the two module types and
their uses within your Asterisk server.
Note: Only qualified service personnel should install the card. Users
should not attempt to perform this function themselves.
FXS Module
The FXS module allows an 800 Series card to initiate and send ringing
voltage to an FXO device such as an analog telephone.
FXO Module
The FXO module allows an 800 Series card to terminate analog telephone
lines (POTS). Because of the modular design, you can activate additional
ports at any time with more FXS or FXO daughter cards. The FXO
module passes all the call features any standard analog telephone line will
support. The phone receiving the call is the last FXO device in the chain.
When it receives voltage from an FXS device, the phone rings.
Digium, Inc. Page 49