Automatic Clock Switching; Clock Configurations - Avaya Nortel Communication Server 1000 Reference

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.

Clock configurations

Clock Controllers can be used in a single or a dual CPU system.
A single CPU system has one Clock Controller card. This card can receive reference clocks
from two sources referred to as the primary and secondary sources. These two sources can
originate from a PRI2, DTI2, etc. PRI2 cards such as the NT8D72BA are capable of supplying
two references of the same clock source. These are known as Ref1 (available at J1) and Ref2
(available at J2) on the NT8D72BA.
The NT5D97 card is capable of supplying two references from each clock source, for example,
four references in total. NT5D97 can supply Clk0 and Clk1 from Unit 0 and Clk0 and Clk1 from
Unit 1. Either Unit 0 or Unit 1 can originate primary source, as shown in
Controller - Option 1
page 288.
Circuit Card Reference
on page 285 through Figure 87: Clock Controller - Option 4
Architecture
Figure 84: Clock
on
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