Timing Cable; Fxo And Fxs Modules - OpenVox A400E User Manual

A400E 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 problem. 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 the details, please refer to HERE.

2.4 FXO and FXS modules

There is so much difference between FXO modules and FXS modules,
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 port and the same with FXS
modules and FXS ports. FXO ports allow A400E connect to PSTN lines
and FXS ports connect to extension sets.
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