Fan Tray; System Backplane - Cisco 7000 Series Hardware Installation And Maintenance Manual

Fan Tray

An array of six individual fans draw cooling air through the chassis interior to maintain an acceptable
operating temperature for the internal components. The fan tray comprises the six fans and a printed
circuit board (with the control circuits) mounted on a metal plate. (See Figure 1-4.) The fan tray
slides into the right side of the chassis from the noninterface processor end of the router. The fans
draw air in through the inlet vents on the opposite side of the chassis, across the processor modules
and other internal components, and out through the exhaust vents adjacent to the fan tray. Figure 1-6
shows the airflow path. The sides of the chassis must remain unobstructed to ensure adequate airflow
and prevent overheating inside the chassis. (See the section "Site Requirements" in the chapter
"Preparing for Installation.")
A fan control board on the fan tray monitors and controls the operation of the variable-speed fans.
The variable-speed feature enables quieter operation by allowing the fans to operate at less than
maximum speed when doing so provides adequate cooling air to maintain an acceptable operating
temperature inside the chassis. A temperature sensor on the RP monitors the internal air temperature.
When the ambient air temperature is within the normal operating range, the fans operate at the
slowest speed, which is 55 percent of the maximum speed. If the temperature inside the chassis
exceeds the normal range, the fan control board increases the fan speed to provide additional cooling
air to the internal components. If the temperature continues to rise, the fan control board linearly
increases the fan speed until the fans reach full speed (100 percent). If the internal temperature
exceeds the specified threshold, the system environmental monitor shuts down all internal power to
prevent equipment damage from excessive heat.
All six fans in the array must be operational. If the system detects a failed or failing fan, it will
display a warning message on the console screen. If the condition is not corrected within two
minutes, the entire system will shut down to avoid an overtemperature condition and shutdown. For
specific thresholds and message descriptions, refer to the section "Environmental Monitoring and
Reporting Functions" in this chapter and to the section "Troubleshooting the Cooling Subsystem" in
the chapter "Troubleshooting the Installation."
The fan tray is available as a spare. Individual fans are not field-replaceable; if a single fan fails, you
must replace the fan tray. The chapter "Maintenance" provides fan tray replacement instructions.

System Backplane

The high-speed CxBus transfers information at 533 Mbps. Figure 1-7 shows the basic system
architecture. The RP, which contains the system processor, and the SP provide distributed processing
and control for the interface processors. The SP (or SSP) controls communication between interface
processors (interface processor-to-interface processor) and the system processor (interface
processor-to-processor).
Physical Description
Product Overview 1-9