AT&T clock

Mark Horton seismo!cbpavo.MIS.OH.ATT.COM!mark
Sun Mar 22 18:23:17 UTC 1987

I am unaware of any master clock in AT&T used for sync.  I do know
that it's quite common for the clock in each central office to run
at a significantly different rate.  The symptom of this is that when
you dial 1200 baud from one CO to another, you get a burst of noise
on a regular basis - the frequency depends on how close the clocks are.
Each time it slips one full tick, there's a phase shift, and with
212 protocol a phase shift turns into a garble.  The problem occurs
with the newer ESS switches.


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