Nortel Communication Server 1000S Installation And Configuration Manual page 92

Page 92 of 394 ISDN Primary Rate Interface equipment overview
Reference clock errors
Automatic clock recovery
553-3001-201 Standard 2.00
The system software checks at intervals of 1 to 15 minutes to see if a clock
controller or reference-clock error has occurred. (The interval of this check
can be configured in LD 73.)
In tracking mode, at any one time, there is one active clock controller which
is tracking on one reference clock. If a clock controller error is detected, the
system switches to the back-up clock controller, without affecting which
reference clock is being tracked.
A reference-clock error occurs when there is a problem with the clock driver
or with the reference clock at the far end. If the clock controller detects a
reference-clock error, the reference clocks are switched.
A command for automatic clock recovery can be selected in LD 60 with the
command EREF.
A DDP loop is disabled when it enters a local-alarm condition. If the local
alarm is cleared, the loop is enabled automatically. When the loop is enabled,
clock tracking is restored in the following conditions:
• If the loop is assigned as the primary reference clock but the clock
controller is tracking on the secondary reference or in free-run mode, it
is restored to tracking on primary.
• If the loop is assigned as the secondary reference clock but the clock
controller is in free-run mode, it is restored to tracking on secondary.
• If the clock check indicates the switch is in free-run mode:
— Tracking is restored to the primary reference clock if defined.
— If the primary reference is disabled or in local alarm, tracking is
restored to the secondary reference clock if defined.
Note: If the system is put into free-run mode by the craftsperson, it
resumes tracking on a reference clock unless the clock-switching option
is disabled (LD 60, command MREF), or the reference clock is
"undefined" in the database.
September 2004