Nortel Networks 1000 - Manual (Page 347)

Architecture 347
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.
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,
Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 02.06 Standard
27 August 2008
Copyright © 2003-2008 Nortel Networks
.