Nortel Circuit Card Installation Manual page 355

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.
Automatic clock recovery
A command for automatic clock recovery can be selected in LD 60 with the
command EREF.
A DDP2 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.
NT5D97 Dual-port DTI2/PRI2 card
Circuit Card
Page 355 of 906
Description and Installation