Chapter 10 Timing; Network Timing - Cisco 15454-DS1-14= - 1.544Mbps Expansion Module Reference Manual

Chapter 10 Timing

10.2 Network Timing

Caution Mixed timing allows you to select both external and line timing sources. However, Cisco does not
recommend its use because it can create timing loops. Use this mode with caution.
Note Only one port can be used for timing related provisioning per line card.
10.2 Network Timing
Figure 10-1 shows an ONS 15454 network timing setup example. Node 1 is set to external timing. Two
timing references are set to BITS. These are Stratum 1 timing sources wired to the BITS input pins on
the Node 1 backplane. The third reference is set to internal clock. The BITS output pins on the backplane
of Node 3 are used to provide timing to outside equipment, such as a digital access line multiplexer.
In the example, Slots 5 and 6 contain the trunk (span) cards. Timing at Nodes 2, 3, and 4 is set to line,
and the timing references are set to the trunk cards based on distance from the BITS source. Reference 1
is set to the trunk card closest to the BITS source. At Node 2, Reference 1 is Slot 5 because it is
connected to Node 1. At Node 4, Reference 1 is set to Slot 6 because it is connected to Node 1. At
Node 3, Reference 1 could be either trunk card because they are an equal distance from Node 1.
Cisco ONS 15454 Reference Manual, R8.5
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