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    Redundant PCGs Overview

    You monitor redundant PCGs to ensure that they generate a clock signal to synchronize the modules and application-specific integrated circuits (ASICs) that make up the Packet Forwarding Engine.

    Redundant PCGs are two PCGs installed in a router. The PCG supplies a 125-MHz system clock to synchronize the modules and ASICs that make up the Packet Forwarding Engine.

    The M40e and M160 routers have two PCGs located at the rear of the chassis in the slots labeled PCG0 and PCG1, to the right of the Routing Engine slots (see Figure 1).

    Figure 1: M40e and M160 Router PCG Location

    M40e and M160 Router
PCG Location

    During normal operation, both PCGs generate a 125-MHz clock signal to the Packet Forwarding Engine modules, along with a signal indicating which is the master clock source. One PCG is designated as the master. The master Routing Engine controls which PCG is master and which is backup.

    The modules and ASICs in the Packet Forwarding Engine that use the clock signal to gate packet processing use only the signal from the master PCG.

    The PCGs are field-replaceable and hot-pluggable. You can remove and replace them without powering down the router, but the routing functions of the system are interrupted when a PCG is removed.

    If the master PCG fails or you remove it from the chassis, the Packet Forwarding Engine resets so that the components start using the signal from the other PCG (which becomes the master). Packet forwarding halts while there is no clock signal because the Packet Forwarding Engine does not accept incoming packets. If the backup PCG fails or is removed, router function is not affected.


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    Published: 2012-08-20