Nortel Circuit Card Installation Manual page 356

Page 356 of 906
Automatic clock switching
Clock configurations
553-3001-211 Standard 3.00
NT5D97 Dual-port DTI2/PRI2 card
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 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 Figure 78 through Figure 81.
There is one Clock Controller cable required for the DDP2 card, which is
available in four sizes; this is the NTCG03AA/AB/AC/AD. Refer to
"Reference clock cables" on
August 2005
page 335 for more information.