Timing Cable; Fxo And Fxs Modules - OpenVox A1200P User Manual

A1200P on DAHDI User Manual

2.3 Timing cable

If you have just one card in the system, all channels on that card have
already run under the same clock source, so timing cable is unnecessary.
But if there are more than one card, using timing cable has some
advantages. Before using the clock line, each card works on its own
clock, therefore precision of the clock is limited; each card will send
/receive voice data at different speeds. In voice usage, this small issue can
be omitted, but in data communication such as Fax/Modem, it will cause
big problems. Data loss will cause communication broken or fax broken.
Timing cable will force all cards to work at the same clock source, send
data at the same speed, as a result no data will lost.
If you found J914 (input) and J915 (output) interfaces on the card, it
means the card supports clock line, for details, please refer to HERE.

2.4 FXO and FXS modules

FXO (Foreign eXchange Office) is the office end of the line,
and FXS (Foreign eXchange Station) is the station end, there is so much
difference between them, they can be identified by color, the former ones
are red and the latter ones are green. FXO modules use FXS signaling
while FXS modules use FXO signaling. FXO modules correspond to
FXO interfaces which receive power (battery) and ring signals, and FXS
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