Nortel Networks NN43001-301 User Manual

Page 72

ISDN Primary Rate Interface equipment overview

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 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.

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.

Clock configurations

Clock Controllers can be used in a single or a dual CPU system.

Nortel Communication Server 1000

ISDN Primary Rate Interface Installation and Commissioning

NN43001-301

02.03

Standard

Release 5.5

7 December 2007