M40e Packet Forwarding Engine Clock Generators (PCGs) Description

The M40e Multiservice Edge Router has two Packet Forwarding Engine Clock Generators (PCGs) installed in the slots at the rear of the chassis that are labeled PCG 0 and PCG 1, as shown in M40e Chassis Description. The PCGs generate a 125-MHz clock signal used to gate packet processing. During startup, the active Routing Engine determines which PCG is master and which is backup, and the MCS relays the decision to the PCGs and to the modules and ASICs in the Packet Forwarding Engine that use the clock signal. The modules and ASICs then use only the signal from the master source.

PCGs are hot-pluggable, as described in M40e Field-Replaceable Units (FRUs). Removal or failure of the backup PCG does not affect router function. When the master PCG fails or is removed from the chassis, however, the Packet Forwarding Engine resets so that the components start using the signal from the other PCG (which becomes the master). The Packet Forwarding Engine cannot accept incoming packets until each PFE component, including the SFM and FPCs, resets to recognize the new master PCG. This can result in traffic halting for several minutes.

For PCG replacement instructions, see Replacing a PCG in an M40e Router.

Each PCG (shown in Figure 1) has the components:

• Signal generator—Provides a 125-MHz system clock signal.
• EEPROM—Stores the serial number and revision level of the PCG.
• Three LEDs—Indicate PCG status. There is a blue one labeled MASTER, a green one labeled OK, and an yellow one labeled FAIL. M40e PCG LEDs describes the LED states.
• Offline button—Prepares the PCG for removal from the router when pressed.

Figure 1: M40e Packet Forwarding Engine Clock Generator

Figure 2 shows the location of the PCGs on the M40e and M160 router chassis.

Figure 2: M40e and M160 Router PCG Location