Specifications

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Cisco IGX 8400 Series Provisioning Guide, Release 9.3.3 and Later Releases
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Chapter 3 Cisco IGX 8400 Series Nodes
Functional Overview
Whenever a clock source changes (because of a line repair or an operator’s command, for example) the
node ensures that the clock path remains hierarchical. Also, whenever a subnetwork is merged with
another subnetwork, each node in the new network verifies that it has the nearest, most stable clock that
is available.
A continuous clock test compares the frequency of the node clock source to a reference on the control
card. If it detects a clock source outside preset frequency limits, the controller declares the source
defective and selects another source.
Ordinarily, a network’s clock sources and line characteristics are configured as part of the node
installation process. Thereafter, clock sources are redefined when a network is reconfigured or a line
status is changed.
Clock sources are manually defined as primary, secondary, or tertiary. The designation typically
depends on the stability of the clock source. Considerations for assessing and defining clock sources
include:
• Stratum level of each clock source
• Reliability of each clock source (Figure 3-1 illustrates clock source reliability)
• Network configuration (topology, backbone, ring, star, mesh, and so on)
• Availability of multiple clock sources in a plesiochronous network (see Figure 3-2)
A plesiochronous network is a network in which there are two or more independent, active clock sources.
For example, a network in which multiple vendors provide multiple lines that require clock mastership
can be a plesiochronous network. Figure 3-1 depicts clock source reliability.