Nortel Networks NN43001-301 - Manual (Page 30)

30 ISDN Primary Rate Interface equipment overview
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 PRI 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:
1. 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.
2. 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:
1. Tracking is restored to the primary reference clock if defined.
2. If the primary reference is disabled or in local alarm, tracking is restored
to the secondary reference clock if defined.
Note: If the switch is put into free-run mode by the craftsperson, it will
resume tracking on a reference clock unless the clock-switching option
has been disabled (LD 60, command MREF), or the reference clock has
been "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:
1. 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.
2. If software is unable to track on the assigned secondary reference clock,
it switches to free run.
QPC720 PRI
The QPC720 PRI card is required for PRI operation in all machine types.
Power requirements
The QPC720 PRI uses power and ground from the backplane. This card
does not require an intelligent bus. Power requirements are:
• +5 volts at 6 amperes
Nortel Communication Server 1000
ISDN Primary Rate Interface Installation and Commissioning
NN43001-301 02.03 Standard
Release 5.5 7 December 2007
Copyright © 2003-2007, Nortel Networks
.