Figure 164: Airflow Through The M120 Router Chassis; Figure 165: M120 Router Front Fan Tray; Figure 166: M120 Router Rear Fan Tray - Juniper M Series Monitoring And Troubleshooting Manual

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M Series and T Series Routers Monitoring and Troubleshooting Guide

Documentation

M320 Router Cooling System

Figure 164: Airflow Through the M120 Router Chassis

The host subsystem monitors the temperature of the router components. When the

router is operating normally, the fans function at lower than full speed. If a fan fails or

the ambient temperature rises above a threshold, the speed of the remaining fans is

automatically adjusted to keep the temperature within the acceptable range. If the

ambient maximum temperature specification is exceeded and the system cannot be

adequately cooled, the Routing Engine shuts down the system by disabling output power

from each PEM.

Both the front and rear card cages pull air from a single intake in the front of the router.

Air is pushed up through both card cages where it combines in a common exhaust plenum

and is exhausted out the upper sides and rear of the system. Some air is circulated back

down through the power supplies and is exhausted out the lower rear area of the chassis

below the power supplies.

Checklist for Monitoring the Cooling System on page 317

The M320 cooling system consists of the following components (see

Figure 167 on