Nortel Meridian 1 Administration And Maintenance page 161

In Example 5, digital connections to the local exchange do exist. When a
second Digital loop from the local exchange becomes available, it can be used
as a Secondary Clock Source in case the Primary Source fails.
Slaves can track on each other as a secondary source since the chances of both
links to the local exchanges going down at the same time are minimal (very
unlikely).
All local exchanges must have a path back to the same stratum 1 source.
Example 5
Alternate clocking from local exchanges
Master Clock
Local
Exchang
loop W
Option 11
LD 60
TRCK PCK
Slave
LD 73:
PREF loop W
SREF loop A
Clocking off Master:
Tracking on Primary
loop W and loop A
used as a secondary
clock source.
Option 11C
Chapter 4 — Network clocking
Master Clock
Local
Exchang
loop X
Option 11
LD 60
TRCK PCK
Slave
LD 73:
loop
PREF loop X
A
SREF loop A
Clocking off Master:
Tracking on Primary
loop X and loop A
used as a secondary
clock source.
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Master Clock
Local
Exchang
loop Y
Option 11
LD 60
TRCK PCK
Slave
LD 73:
loop
PREF loop Y
B
SREF loop B
Clocking off Master:
Tracking on Primary
loop Y and loop B
used as a secondary
clock source.
553-7565.EPS