To make it simpler, observe the following diagram, describing the
location of each of these interfaces.
On examining the above diagram, one would immediately notice that the FXO
interface is located at the receiving end of the connection, while the FXS interface is
the one originating the service. This means that one cannot exist without the other;
to work an FXO interface on one side requires an FXS interface on the other and
vice versa.
Another way of thinking about it would be that analog telephony requires the
generation of on-hook and off-hook signalling to the network generated by an
FXO interface. Thus, the FXO interface would be connected to a device capable of
generating these signals??”an analog phone device or the incoming port of a PBX. The
FXS interface would be the one capable of reading these signals, a device capable of
generating tones and voltage??”thus the connection at the Central Office Exchange or
the PBX outgoing extension port.
While Asterisk is capable of handling other types of signalling interfaces, the
above-mentioned interfaces are the most common interfaces that you will ever use.
To learn more about FXS and FXO interface, please visit the
voip-info.org website.
voip-info.org on FXO:
http://www.
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