[asterisk-users] FXO Cards vs. Channel bank with T1

[Tzafrir Cohen]

On Wed, Nov 01, 2006 at 09:08:43AM -0600, Ejay Hire wrote:
> This is incorrect.  The data is still packetized and passed through IP which
> provides the same echo cancellation and distortion issues as a call that
> passed through an FXO/FXS card.

The issue here is an "implementation bug" of Zaptel rather than a
fundemental archtectual flaw.

For fax or modem to work well you need a good line. One of the problems
that may cause line quality problems is different clock speeds of
different components of the system. They may cause an occasional "click"
every number of seconds.

The problem I referred to is that different Zaptel cards may have a
different clock. Asterisk uses the clock of the "master" zaptel device,
but it is not exactly clear who that master device is (basically: the
first Zaptel device). No other device tries to get clocking from it.

If you use an external channel bank you work around the problem by
connecting all the external connections (both PRI lines and channel bank
FXO/FXS lines) through the same PRI card. That card will not have a
problem being in sync with itself.

As for our device: our short-term solution is to sync the PC clock from
Zaptel as we can already sync our device from the PC. But the long term
solution is to sync our device (and other zaptel devices) from the
master zaptel device.

-- 
               Tzafrir Cohen       
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