Digium, Inc.
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Chapter 4
FXS and FXO Explained
Identification
There are multiple standard configurations in which an Analog 410 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 Analog 410 Series card to initiate and send
ringing voltage to an FXO device such as an analog telephone.
FXO Module
The FXO module allows an Analog 410 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.
