Understanding Redundant Cooling System Components ! 529
Chapter 39: Monitoring Redundant Cooling System Components
M40 Router Redundant Cooling System Components
The M40 router cooling system consists of three separate subsystems (see
Figure 214):
! Impellers—Two redundant pairs of impellers (top impeller and bottom impeller)
cool the Packet Forwarding Engine components (backplane, System Control
Board [SCB], FPCs, and Physical Interface Cards [PICs]). During normal
operation, both pairs of impellers function at less than full capacity.
! Triple fan assemblies—Three load-sharing fans cool the backplane and the
Routing Engine (rear left fan, rear center fan, and rear right fan).
! Power supply integrated fan—A built-in fan cools each power supply.
Each cooling subsystem maintains a separate airflow, and each is monitored
independently for temperature control. Figure 214 shows the M40 router cooling
system airflow.
Temperature sensors on the backplane, the SCB, and the FPCs control the speed of
the impellers. Impeller failure triggers the red alarm LED on the craft interface. If
the temperature passes a certain threshold, the JUNOS software turns off the power
supplies.
The M40 router is designed to run normally with all three fans sharing the load
equally and running at half speed.
Figure 214: M40 Router Cooling System and Airflow
Power supply
and Fans
Lower impellers
Packet
Forwarding
Engine
Upper impellers
Routing
Engine
Fan tray
Backplane
Air intake for
power supply cooling
Air intake for
Routing Engine cooling
Exhaust for Routing
Engine and backplane
cooling
Air intake for
Packet Forwarding
Engine cooling
Front
of Chassis
Rear
of Chassis
Exhaust for
power supply
Exhaust for
Packet Forwarding
Engine cooling
1771
Top impeller
Bottom impeller
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