Table Of Contents
16-Slot Line Card Chassis Airflow
16-Slot Line Card Chassis Fan Tray
16-Slot Line Card Chassis Fan Controller Card
Chassis Cooling System
This chapter describes the components that make up the cooling system of the Cisco CRS-1 Carrier Routing Sysetm 16-Slot Line Card Chassis. It contains the following sections:
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16-Slot Line Card Chassis Airflow
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Cooling System Overview
The cooling system dissipates the heat generated by the line card chassis and controls the temperature of chassis components. The cooling system has a fully redundant architecture that allows the chassis to continue operating with a single-fault failure (such as a single fan or fan tray failure). See the "Fan Controller Redundancy" section for more information. The architecture also supports a redundant load-sharing design.
The complete chassis cooling system includes:
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The power modules in the power shelves also have their own self-contained cooling fans.
All nine fans in a fan tray operate as a group. So, if it is necessary to increase or decrease airflow, all of the fans in the tray increase or decrease their rotation speed together. When two fan trays are operational in a chassis, the speed of fans in both trays is adjusted together.
Thermal sensors (inlet, exhaust, and hot-spot) located throughout the Cisco CRS-1 16-slot line card chassis are used to monitor temperature readings and identify when the system is not cooling properly.
Software running on several types of service processor (SP) modules is used to control the operation of the fans. These SP modules are connected by internal Ethernet to the system controller on the route processor (RP).
16-Slot Line Card Chassis Airflow
The airflow through the Cisco CRS-1 16-slot line card chassis is controlled by a push-pull configuration (see Figure 3-1). The bottom fan tray pulls in ambient air from the bottom front of the chassis and the top fan pulls the air up through the card cages where the warm air is exhausted out the top rear of the chassis.
Figure 3-1 Airflow Through 16-Slot Line Card Chassis
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The chassis has a replaceable air filter mounted in a slide-out tray above the lower fan tray. The Cisco CRS-1 16-slot line card chassis air filter, shown in Figure 3-2, plugs into the rear (MSC) side of the chassis.
You should change the air filter as often as necessary. In a dirty environment, or when you start getting frequent temperature alarms, check the intake grills for debris and check the air filter to see if it needs to be replaced. Before removing the air filter for replacing, you should have a spare filter on hand. Then, when you remove the dirty filter, install the spare filter in the chassis.
Figure 3-2 Air Filter
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Cooling System Operation
The fan control software and related circuitry varies the DC input voltage to individual fans to control their speed. This increases or decreases the airflow needed to keep the line card chassis operating in a desired temperature range. The chassis cooling system uses multiple fan speeds to optimize cooling, acoustics, and power consumption. There are four normal operating fan-speeds and one high-speed setting used when a fan tray has failed.
At initial power up, control software powers on the fans to 4300 to 4500 RPM. This provides airflow during system initialization and software boot, and ensures that there is adequate cooling for the chassis in case the software hangs during boot. The fan control software initializes after the routing system software boots, which can take 3 to 5 minutes. The fan control software then adjusts the fan speeds appropriately.
During normal operation, the chassis averages the temperatures reported by inlet temperature sensors in the lower card cage (or in the upper card cage if the lower cage is empty). To determine the appropriate fan speed for the current temperature, the fan control software compares the averaged inlet temperature to a lookup table that lists the optimal fan speed for each temperature. The software then sets the fan speed to the appropriate value for the current temperature. The temperature ranges in the lookup table overlap to ensure a proper margin to avoid any type of fan speed oscillation occurring between states.
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Thermal Alarms
Local thermal sensors (on individual cards) monitor temperatures and generate a thermal alarm when the cooling system is not cooling properly. A temperature sensor might trip in response to elevated ambient air temperature, a clogged air filter or other airflow blockage, or a combination of these causes. A fan failure causes a fault message, but if no thermal sensors have tripped, the fan control remains unchanged.
When a thermal sensor reports a thermal alarm, the sensor passes the fault condition to its local service processor (SP), which then notifies the system controller on the route processor (RP). The system controller passes the fault condition to the SP on each fan controller board. The fan control software then takes appropriate action to resolve the fault.
When a thermal sensor trips, the fan control software tries to resolve the problem (for example, by increasing fan speed). The software performs a series of steps to prevent chassis components from getting anywhere near reliability-reducing, chip-destroying temperatures. If the fault continues, the software shuts down the card or module to save components.
Quick-Shutdown Mode
The fan controller cards and fan trays have a quick-shutdown mode that kills power when a card or fan tray is disengaged from the chassis midplane. The quick-shutdown mode minimizes inrush current during a hot swap or OIR. In normal maintenance conditions, the software gracefully shut downs the power to the failed part, allowing ample time for capacitors to discharge.
Fan Controller Redundancy
The redundant architecture of the cooling system allows the cooling system to continue operating even when certain components have failed. The cooling system can withstand the failure of any one of the following components and still continue to properly cool the line card chassis:
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A double-fault fan failure involves two fan trays, two fan tray boards, two fan controller cards, two power shelves, two power modules (DC PEMs or AC rectifiers), or any combination of two of these units. If a double-fault failure occurs, the chassis remains powered on, unless both fan trays have failed or thermal alarms indicate a problem serious enough to power down the chassis. The failure of multiple fans is not considered a double-fault failure because multiple fans can fail without impacting cooling.
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Both fan controller cards work together to provide fully redundant input power and control logic for fan trays and fans. Each fan controller card receives its input power (-48 VDC) from both the A and B power shelves. The fan controller card then provides one fan tray with input power from its "A" bus and provides power to other fan tray from its "B" bus. This ensures that the upper fan tray is powered from the "A" bus on one fan controller card and from the "B" bus on the second fan controller card.
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16-Slot Line Card Chassis Fan Tray
Figure 3-3 shows a fan tray, which plugs into the rear (MSC) side of the chassis. Each fan tray is hot-swappable and is considered a field-replaceable unit. The chassis is designed to run with both fan trays in place.
Figure 3-3 Fan Tray
Each fan tray contains:
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The fan tray has the following physical characteristics:
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16-Slot Line Card Chassis Fan Controller Card
A Cisco CRS-1 16-slot line card chassis contains two line card chassis fan controller (LCFC) cards, shown in Figure 3-4.
Figure 3-4 16-Slot Line Card Chassis Fan Controller (LCFC) Card
The line card chassis fan controller cards provide the following functions:
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The line card chassis fan controller cards also contain the circuitry and input connector for the building integrated timing source (BITS) clock. See Chapter 7, "Single-Shelf System Summary,"for more information.
Figure 3-5 shows the fan controller card front panel.
Figure 3-5 Fan Controller Card Front Panel
The physical characteristics of the fan controller card are:
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