Specifications

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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
• On every port with NCDP enabled, NCDP establishes a control VC to carry configuration and
network topology information between the connected nodes. On non-virtual trunks, the control VC
is established by default on VPI 0, VCI 34. If you change the VPI/VCI within the limits of the
minimum or maximum range, then the control VC will be established on the new VPI/VCI.
• BITS clock interfaces receive Stratum-3 or higher clock signals.
• NCDP supports a maximum of 200 nodes in an NCDP domain. If your network has more than 200
nodes, multiple, smaller NCDP domains should be established. Typically, NCDP domains follow
PNNI peer group boundaries.
• When using an external clock source and redundant PXM cards, use a Y-cable to connect that clock
source to the same clock port on both PXM cards. Do not run separate external clock sources to each
card because this can produce timing problems.
• If a failed clock source recovers, the switch will not revert to the recovered clock source unless you
re-add it to the node with the cnfncdpclksrc command.
• Primary and secondary BITS clocks can be configured after the switch is initialized. For more
information, see the “Configuring Clock Sources” section in Chapter 2, “Configuring General
Switch Features.”
To develop an NCDP network clock source plan, create a topology drawing and identify all the
configured clock sources on each switch in the network. Identify the priority of each clock source. You
may also want to identify any NNI ports where you plan to disable NCDP.