Cisco MGX 8830, Руководство по настройке

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Cisco MGX 8850 (PXM1E/PXM45), Cisco MGX 8950, Cisco MGX 8830, and Cisco MGX 8880 Configuration Guide
Release 5.0.10, OL-3845-01 Rev. B0, August 16, 2004
Chapter 1 Preparing for Configuration
Guidelines for Creating a Network Clock Source Plan
have NCDP enabled. NCDP automatically selects an internal oscillator on one of the NCDP nodes to be
the root clock source. Each NCDP node in the network is synchronized to this root clock reference. If
you do not want the root clock source to be an internal oscillator, you can configure it to come from an
external source with the cnfncdpclksrc command, as described in the
“Managing NCDP Clock Sources”
section Chapter 9, “Switch Operating Procedures.”
NCDP uses the following criteria to find the best root clock source for the network:
• Priority (should be sufficient to find the root)
•
Stratum level (should be sufficient as a tie-breaker)
• Clock source reference
• ATM address of the switch
You can modify the clock priority, stratum level of the Bits source, and clock source reference through
the cnfncdpclksrc command, as described in the
“Managing NCDP Clock Sources” section in
Chapter 9, “Switch Operating Procedures.”
Figure 1-8 shows an example NCDP network clock source topology. The numbers represent the priority
of each network clock source, with 1 being the highest priority (or second best clock source) and 10
being the lowest priority. In this example, if the root clock source fails, the clock source with priority 1
takes over as the root clock. If the new root clock source with priority 1 fails, then the clock source with
priority 2 takes over as the root, and so forth.
Figure 1-8 Example NCDP Source Topology
Consider the following information when you create your NCDP network clock source plan:
•
You must enable NCDP on a per-node basis because manual clocking is the default method of clock
synchronization.
• Clock sources that are located near the center of the network minimize clock signal propagation
delay.
• Once you enable NCDP, it is enabled on all NNI ports on the local switch by default. This includes
PNNI ports, IISP ports, and AINI ports.
•
NCDP is disabled on virtual trunks by default.
• You can add clock sources to any UNI or clocking ports on the node.
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Root clock
source
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