Nortel Networks 553-3001-211 manual Automatic clock recovery

NT5D97 Dual-port DTI2/PRI2 card Page 343 of 894

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.

Circuit Card Description and Installation