Specifications

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Cisco MGX 8800/8900 Series Software Configuration Guide
Release 5.1, Part Number OL-6482-01, Rev. A0, January 25, 2005
Chapter 1 Preparing for Configuration
Guidelines for Creating a Network Clock Source Plan
Note Manual clock configuration and NCDP configuration operate independently of one another. In other
words, you can configure both versions of network clock sourcing on your network. However, only one
version can be enabled at a time. You cannot run your manual network clock configuration on your
network while NCDP is running, and vice-versa.
However, both configurations are stored in the disk database. Therefore, if you disable NCDP, the
network reverts back to your original manual network clock configuration. If you enable NCDP on that
same network at a later point, the network will revert back to the previous NCDP configuration.
Note On MGX 8850 (PXM1E), MGX 8850/B, and MGX 8830 switches, clock source configuration is done
on the PXM1E card and passed to other nodes over PXM1E lines.
On MGX 8850 (PXM45), MGX 8830/B, and MGX 8950 switches, clock source configuration is done
on a PXM45 card, and clock sourcing information is passed to other nodes over NNI trunks connected
to service modules.
Planning for Manual Clock Synchronization
In manual clock source configurations, you need to configure a primary and secondary clock source,
which are distributed throughout the network. All nodes have an internal Stratum-3 clock that serves as
a tertiary clock source. The secondary clock source takes over if the primary clock source fails, and the
tertiary clock source takes over if the secondary clock source fails.
If no clock sources are configured, the switch uses the internal Stratum-3 clock source. If only a primary
clock source is configured, the internal Stratum-3 clock takes over in the event of a primary clock source
failure. Figure 1-6 shows an example network clock source topology.