Nortel Networks NN43001-301 manual Reference clock errors

NT5D97 Dual-port DTI2/PRI2 card 51

Reference clock errors

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.

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.

Automatic clock switching

If the EREF command is selected in LD 60, tracking on the primary or secondary reference clock is automatically switched in the following manner:

•If software is unable to track on the assigned primary reference clock, it switches to the secondary reference clock and sends appropriate DTC maintenance messages.

•If software is unable to track on the assigned secondary reference clock, it switches to free run.

Nortel Communication Server 1000

ISDN Primary Rate Interface Installation and Commissioning

NN43001-301 02.03 Standard

Release 5.5 7 December 2007

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