Juniper M40 Hardware manual
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Chapter 2
Hardware Component Overview
This chapter provides an overview of the hardware components on the M40 Internet router:
Packet Forwarding Engine on page 9
Physical Interface Cards (PICs) on page 10
Flexible PIC Concentrators (FPCs) on page 11
System Control Board (SCB) on page 13
Cable Management System on page 24
Hardware Component Overview
7
Chassis
Chassis
The router chassis is a rigid sheet metal structure that houses all the other router hardware
components (see Figure 1 and Figure 2). The chassis is 19 in. (48 cm) wide and 23.5 in.
(60 cm) deep. The chassis height of 35 in. (89 cm) enables stacked installation of two M40 routers in a single floor-to-ceiling rack. The two front- or center-mounting ears (one on each side) enable installation into either a front-mount or a center-mount rack. For more information, see “Rack Requirements” on page 39.
The chassis includes two electrostatic discharge (ESD) points (banana plug receptacles), one
front and one rear, as shown in Figure 1 and Figure 2.
Before removing or installing components of a functioning router, attach an ESD strap to one of the ESD points and place the other end of the strap around your bare wrist.
Failure to use an ESD strap could result in damage to the router.
The router must be connected to earth ground during normal operation.
For further safety information, see “Regulatory
Compliance and Safety Information” on page 55.
Figure 1: Front View of Chassis
Front rack-mounting ear
Cable managment system
Card cage
Backplane
Slide guides for FPCs
ESD point
Craft interface
Air filter
Center rack-mounting ear
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M40 Internet Router Hardware Guide
Packet Forwarding Engine
Figure 2: Rear View of Chassis
Upper impeller assembly
Front rack-mounting ear
Center rack-mounting ear
Fan tray
Routing Engine housing
LS-120 drive
ESD point
Power supply A
Power supply B
Packet Forwarding Engine
The Packet Forwarding Engine is a multicomponent system that uses application-specific integrated circuits (ASICs) to perform Layer 2 and Layer 3 packet switching, route lookups, and packet forwarding. The ASICs include the Distributed Buffer Manager ASIC, I/O Manager
ASIC, Internet Processor or Internet Processor II ASIC, and various media-specific controllers.
The Packet Forwarding Engine has the following components:
Backplane—Forms the rear of the FPC card cage, distributes power from the power
supplies, and transfers packets and signals between router components, which plug into it.
Physical Interface Cards (PICs)—Physically connect the router to network media such as
OC-12 ATM, OC-12 and OC-48 SONET/SDH, Channelized OC-12, and Gigabit Ethernet.
PICs are housed in FPCs.
Flexible PIC Concentrators (FPCs)—Process incoming and outgoing packets. From one
to eight FPCs can plug into the backplane from the front of the chassis. Each FPC accommodates up to four Physical Interface Cards (PICs).
System Control Board (SCB)—Performs route lookup, filtering, and switching. The SCB
installs into the backplane from the front of the chassis.
Hardware Component Overview
9
Packet Forwarding Engine
Backplane
Figure 3: The Backplane
The backplane is a panel that forms the back of the FPC card cage (see Figure 3). The SCB
and all the FPCs install into the backplane from the front of the chassis. The backplane contains a temperature sensor and is cooled by three fans operating in unison. It also contains an EEPROM that stores the serial number and revision level of the backplane.
The backplane performs the following functions:
Power distribution—The backplane distributes power to all router components from the power supplies attached to it.
Signal connectivity—The backplane transports the signals exchanged by system components for monitoring and control purposes.
Management of shared memory on the FPCs—One Distributed Buffer Manager ASIC on the backplane uniformly allocates incoming data packets throughout shared memory on the FPCs.
Transfer of outgoing data cells to the FPCs—A second Distributed Buffer Manager ASIC on the backplane passes data cells to the FPCs for reassembly into packets when the data is ready to be transmitted.
Backplane
Physical Interface Cards (PICs)
Physical Interface Cards (PICs) are housed on Flexible PIC Concentrators (FPCs) and
physically connect the router to network media. For information about FPCs, see “Flexible
PIC Concentrators (FPCs)” on page 11. The router supports various PICs, including ATM,
Channelized OC-12/STM-4, Gigabit Ethernet, and SONET/SDH interfaces. Up to four PICs install in each FPC. The PIC slots are numbered
0
(zero) through
3
, top to bottom.
PICs receive incoming packets from the network and transmit outgoing packets to the network, performing framing and line-speed signaling for their media type as required. PICs also encapsulate outgoing packets received from the FPCs before transmitting them. The controller ASIC on each PIC performs additional control functions specific to the PIC media type.
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M40 Internet Router Hardware Guide
Packet Forwarding Engine
A regular PIC is hot-removable and hot-insertable in the sense that its absence does not disrupt routing functions; however, you must completely remove its host FPC from the chassis before removing the PIC, which affects all PICs on the FPC. For replacement instructions, see “Replace a PIC” on page 167.
Quad-wide PICs, such as the 4-port Gigabit Ethernet and OC-48/STM-16 SONET/SDH PICs, occupy an entire FPC slot and are hot-removable and hot-insertable, as described in
“Field-Replaceable Units (FRUs)” on page 4. The instructions for replacing a quad-wide PIC are the same as for an FPC. See “Replace an FPC or Quad-wide PIC” on page 163.
PIC Components
Most PICs supported on the M40 router have the following components, but for complete specifications see the M20 and M40 Internet R outers PIC Guide . For information about pinouts for PIC cable connectors, see “Cable Connectors and Pinouts” on page 207.
One or more cable connector ports—Accept a network media connector.
LEDs—Indicate PIC and port status. Most PICs have an LED labeled
STATUS
on the PIC faceplate. Some PICs have additional LEDs, often one per port. The meaning of the LED states differs for various PICs. For more information, see the M20 and M40 Internet
Routers PIC Guide .
Flexible PIC Concentrators (FPCs)
Flexible PIC Concentrators (FPCs) house the PICs that connect the router to network media
(for information about PICs, see “Physical Interface Cards (PICs)” on page 10). Up to eight
FPCs install vertically into the backplane from the front of the chassis. The FPC slots are numbered left to right, from 0 (zero) through 7 . Each FPC accommodates up to four PICs and the PIC slots in each FPC are numbered from
0
(zero) through
3
, top to bottom.
An FPC can be installed into any FPC slot, regardless of the PICs it contains, and any combination of slots can be used. If a slot is empty, you must install a blank FPC panel to
shield it, so that cooling air can circulate properly throughout the card cage. Figure 4, which
shows a chassis with an FPC in slot 7 , omits the blank FPC panels to show the FPC’s position in the card cage.
The main function of an FPC is to connect the PICs installed in it to the other router components. The I/O Manager ASIC on the FPC divides each incoming data packet into
64-byte cells, which the Distributed Buffer Manager ASIC on the backplane distributes among the memory buffers located on and shared by all installed FPCs. After the SCB decides how to forward a packet, the I/O Manager ASIC on the FPC reassembles the corresponding data cells back into network-packet form and passes the packet to the appropriate PIC for transmission to the network. For more information, see “Data Flow through the Packet Forwarding
Engine” on page 33.
FPCs are hot-removable and hot-insertable, as described in “Field-Replaceable Units (FRUs)” on page 4. When you remove or install an FPC, packet forwarding halts for about 200 ms while the Packet Forwarding Engine adjusts to the change in the amount of memory available in the pool located on and shared by all FPCs. When you install an FPC into a functioning router, press its offline button to activate it and the PICs installed in it. The
Routing Engine downloads the FPC software, the FPC runs its diagnostics, and the PICs housed on the FPC are enabled. Forwarding continues uninterrupted during this process. For
FPC replacement instructions, see “Replace an FPC or Quad-wide PIC” on page 163.
Hardware Component Overview
11
Packet Forwarding Engine
The PICs that install on both types of FPC are also hot-removable and hot-insertable. For
more information, see “Physical Interface Cards (PICs)” on page 10.
Figure 4: FPC Installed in Slot FPC7
STATU S
RX
TX
LINE
RX AC
TIVITY
7
FPC Components
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M40 Internet Router Hardware Guide
Each FPC contains the following components:
FPC card carrier—Houses the other FPC components.
I/O Manager ASIC—Parses Layer 2 and Layer 3 data and performs encapsulation and segmentation.
Two identical SDRAM dual inline memory modules (DIMMs)—Form the memory pool shared with the other FPCs installed in the router.
Parity-protected SSRAM—Stores data structures used by the I/O Manager ASIC.
Processor subsystem—Manages packet handling in the FPC and communication with the SCB. It is a PowerPC 603e-based CPU with parity-protected DRAM.
EEPROM—Stores the serial number and revision level of the FPC.
Two LEDs—Indicate FPC status. There is a green one labeled OK and a red one labeled
FAIL
. The LEDs for each FPC are located directly below it, on the router craft interface.
For more information, see “FPC LEDs and Offline Button” on page 18.
Offline button—Prepares the FPC for removal from the router when pressed. Like the
LEDs, an offline button is located on the craft interface directly below each FPC slot. For
more information, see “FPC LEDs and Offline Button” on page 18.
Extractor clips—Control the locking system that secures the FPC in the card cage.
Packet Forwarding Engine
System Control Board (SCB)
The System Control Board (SCB) performs route lookup, filtering, and switching on incoming data packets, then directs outbound packets to the appropriate FPC for transmission to the network. It occupies the center slot of the card cage, installing into the backplane from the
front of the chassis (see Figure 1).
The SCB is hot-pluggable, as described in “Field-Replaceable Units (FRUs)” on page 4. For
SCB replacement instructions, see “Replace the SCB” on page 169.
The SCB performs the following functions:
Route lookups—The Internet Processor or Internet Processor II ASIC on the SCB performs route lookups using the forwarding table stored in the synchronous SRAM
(SSRAM). After performing the lookup, the ASIC informs the backplane of the forwarding decision, and the backplane forwards the decision to the appropriate outgoing interface.
Monitoring and control of router components—The SCB collects statistics from all sensors in the system. When it detects a failure or alarm condition, it sends a signal to the Routing Engine, which generates control messages or sets an alarm. The SCB also relays control messages from the Routing Engine to the router components.
Transfer of exception and control packets—The Internet Processor or Internet Processor
II ASIC passes exception packets to the microprocessor on the SCB, which processes almost all of them. The SCB sends any remaining exception packets to the Routing
Engine for further processing. When the SCB detects an error originating in the Packet
Forwarding Engine, it sends it to the Routing Engine using system logging (syslog) messages.
Control of FPC resets—If the SCB detects errors in an FPC, it attempts to reset the FPC.
After three unsuccessful reset attempts, the SCB takes the FPC offline and informs the
Routing Engine. Other FPCs are unaffected, and system operation continues.
SCB Components
The SCB (shown in Figure 5) has the following components:
One Internet Processor or Internet Processor II ASIC—Performs route lookups and makes routing decisions.
Parity-protected SSRAM—Stores the forwarding table.
Processor subsystem—Manages SCB functions and handles exception packets. The processor has the following components:
One PowerPC 603e processor
Parity-protected Level 2 cache
Parity-protected DRAM
EEPROM—Stores the serial number and revision level.
Hardware Component Overview
13
Packet Forwarding Engine
19.44-MHz stratum 3 reference clock—Generates clock signal for SONET/SDH PICs.
I
2
C controller—Monitors the status of router components.
Debug port—Connects the SCB to a laptop or other monitoring device through an
RS-232 (EIA-232) serial cable. It uses a DB-25 connector.
Four LEDs—Indicate SCB status. There are two green ones labeled
ACTIVE and
RUN
, and two amber ones labeled STAT1 and STAT2
. Table 4 describes the LED states.
Reset switch—Restarts the SCB when pressed, causing the Packet Forwarding Engine to reset and halting packet forwarding for up to approximately two minutes. Do not use the reset switch under normal circumstances; to access it, push the end of a paper clip or other small probing device through the hole in the SCB faceplate.
Extractor clips—Control the locking system that secures the SCB in the chassis.
For specific information about SCB components (for example, the amount of SSRAM and DRAM), issue the show chassis scb command.
Figure 5: System Control Board
Access to reset switch
LEDs
Debug port
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M40 Internet Router Hardware Guide
Routing Engine
Table 4: States for SCB LEDs
Label Color State
ACTIVE Green Flashing (pulsed with out-time proportional to traffic)
RUN Green Blinking
STAT1
STAT2
Amber Flashing
Description
I/O interrupts are occurring.
SCB processor is running. Normally, the blinking is faint and becomes bright only when the SCB is processing many exceptions.
Internal diagnostics are running.
Routing Engine
The Routing Engine is an Intel-based PCI platform that runs JUNOS Internet software.
Software processes that run on the Routing Engine maintain the routing tables, manage the routing protocols used on the router, control the router's interfaces, control some chassis components, and provide the interface for system management and user access to the router.
The Routing Engine installs into the rear of the chassis, in a compartment behind the card
cage (see Figure 2). For information about the routing architecture, see “System Architecture
Overview” on page 31.
The Routing Engine is hot-pluggable, as described in “Field-Replaceable Units (FRUs)” on page 4. For replacement instructions, see “Maintain and Replace Routing Engine
Components” on page 173.
Routing Engine Components
The Routing Engine (shown in Figure 6) is a two-board system with the following
components:
CPU—Runs JUNOS Internet software to maintain the router’s routing tables and routing protocols. It has a Pentium-class processor.
SDRAM—Provides storage for the routing and forwarding tables and for other Routing
Engine processes.
Compact flash drive—Provides primary storage for software images, configuration files, and microcode. The drive is fixed and inaccessible from outside the router.
Hard drive—Provides secondary storage for log files, memory dumps, and rebooting the system if the flash drive fails.
PC card slot—Accepts a removable PC card, which stores software images for system upgrades.
Interfaces for out-of-band management access—Provide information about Routing
Engine status to devices (console, laptop, or terminal server) that can be attached to access ports located on the craft interface
.
EEPROM—Stores the serial number of the Routing Engine.
Hardware Component Overview
15
Routing Engine
Figure 6: Routing Engine
Routing Engine 333
Extractor clip
LED—Indicates disk activity for the internal IDE interface. It does not necessarily indicate routing-related activity.
The LEDs that report Routing Engine status are on the craft interface rather than the
Routing Engine faceplate. See “Routing Engine LEDs and Interface Ports” on page 19.
Reset button—Reboots the Routing Engine when pressed.
Extractor clips—Control the locking system that secures the Routing Engine in the chassis.
The appearance and position of electronic components or the PC card slot on your Routing Engine might differ from the figures in this section. These differences do not affect
Routing Engine installation and removal or functionality.
For specific information about components in a Routing
Engine (for example, the capacity of the hard disk), issue the show chassis routing-engine command.
Although the Routing Engine has a PC card slot, it is disabled on the M40 router. The router instead uses an
LS-120 disk.
LED
PC card slot
Extractor clip
Routing Engine 600
Extractor clip
JUNIP
ER NE
TWOR
KS LAB
EL THIS
SIDE
PC card slot
LED
Extractor clip
16
M40 Internet Router Hardware Guide
Craft Interface
Craft Interface
Figure 7: Craft Interface
The craft interface provides status and troubleshooting information at a glance and has buttons for deactivating alarms and preparing FPCs for removal. The craft interface is located
on the front of the chassis below the FPC card cage, as shown in Figure 1. It includes the
FPC LEDs
NC
C
NO
NC
C
NO
FAIL
0
OK FAIL OK FAIL
1
ALARM
RED
ALARM
YELLOW
ALARM
ALARM
CUTOFF
2
OK FAIL
3
OK FAIL
4
MENU
ENTER
OK FAIL
5
OK FAIL OK FAIL
6 7
ROUTING ENGINE
OK
FAIL
CONSOLE
MANAGEMENT
ETHERNET
AUXILIARY
OK
Alarm relay contacts
Alarm LEDs
LCD
Routing Engine LEDs Routing Engine ports
The power supply LEDs are located on the power supply faceplate, rather than on the craft interface. For more
information, see “Power Supplies” on page 20.
For information about the elements on the craft interface, see the following sections:
FPC LEDs and Offline Button on page 18
Alarm Relay Contacts, LEDs, and Cutoff Button on page 18
Routing Engine LEDs and Interface Ports on page 19
Hardware Component Overview
17
Craft Interface
FPC LEDs and Offline Button
Each of the eight FPC slots in the router has two LEDs and an offline button located directly
below it on the craft interface, as shown in Figure 7. The green LED labeled
OK
and red LED labeled FAIL
indicate FPC status, as described in Table 5.
The offline button, labeled with the FPC slot number (for example, 4 ), prepares the FPC for removal from the router when pressed. Press and hold the button for about 5 seconds, until the FAIL LED lights.
Table 5: States for FPC LEDs
Label Shape Color State
OK Green On steadily
Blinking
FAIL Red On steadily
Description
FPC is functioning normally.
FPC is starting up.
FPC has failed or is offline.
Alarm Relay Contacts, LEDs, and Cutoff Button
The area labeled ALARM at the left side of the craft interface contains two alarm LEDs and
relay contacts, and the alarm cutoff button (see Figure 7). The circular LED, labeled
RED ALARM , lights to indicate a critical condition that can result in a system shutdown. The triangular LED, labeled
YELLOW ALARM
, lights to indicate a less severe condition that requires monitoring or maintenance. Both LEDs can be lit simultaneously. The LCD on the craft interface reports the cause of the alarm.
To the left of the LEDs are the corresponding relay contacts for connecting the router to external alarm-reporting devices. A system condition that causes the red or yellow alarm LED to light on the craft interface also activates the corresponding alarm relay contact. For instructions for attaching a device to the alarm relay contacts, see “Connect to an External
Alarm-Reporting Device” on page 121.
To deactivate red and yellow alarms, press the button labeled
ALARM CUTOFF
, which is located to the right of the alarm LEDs. Deactivating an alarm turns off both LEDs and deactivates the device attached to the corresponding alarm relay contact. However, the LCD continues to report the alarm message until you clear the condition that caused the alarm.
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M40 Internet Router Hardware Guide
Craft Interface
Table 6 describes the alarm LEDs and alarm cutoff button in more detail.
Table 6: Alarm LEDs and Alarm Cutoff Button
Shape
ALARM
CUTOFF
Color State
Red On steadily
Description
Critical alarm LED—Indicates a critical condition that can cause the router to stop functioning. Possible causes include component removal, failure, or overheating.
Yellow On steadily Warning alarm LED—Indicates a serious but nonfatal error condition, such as a maintenance alert or a significant increase in component temperature.
— — Alarm cutoff button—Deactivates red and yellow alarms and reset timers for system maintenance alerts.
LCD
A four-line LCD is located in the center part of the craft interface, next to six navigation
buttons (see Figure 7). The LCD operates in two modes:
Idle mode—Reports current system status during normal operation.
Alarm mode—Reports alarm conditions when the red or yellow alarm LED is lit. For a list of alarm messages that can appear on the LCD, see “Hardware and Interface Alarm
Messages” on page 192.
Routing Engine LEDs and Interface Ports
The area labeled ROUTING ENGINE at the right side of the craft interface contains Routing
Engine status LEDs and three ports for connecting the Routing Engine to external devices on which system administrators can issue JUNOS command-line interface (CLI) commands to manage the router.
The green LED labeled
OK
and red LED labeled
FAIL
indicate Routing Engine status, as
Table 7: States for Routing Engine LEDs
Label Shape Color State
OK Green On steadily
Blinking
Description
System Control Board detects presence of the Routing
Engine.
Routing Engine is starting up.
FAIL Red On steadily Routing Engine is not operational, or System Control
Board does not detect its presence.
Hardware Component Overview
19
Power Supplies
The interface ports with the indicated label function as follows:
MANAGEMENT ETHERNET —Connects the Routing Engine through an Ethernet connection to a management LAN (or any other device that plugs into an Ethernet connection) for out-of-band management. The port uses an autosensing RJ-45 connector to support both
10- and 100-Mbps connections.
CONSOLE
—Connects the Routing Engine to a system console through an RS-232
(EIA-232) serial cable.
AUXILIARY — Connects the Routing Engine to a laptop, modem, or other auxiliary device through an RS-232 (EIA-232) serial cable.
For information about the pinouts for the connectors, see “Cable Connectors and Pinouts” on page 207.
Power Supplies
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M40 Internet Router Hardware Guide
The router can use either AC or DC power. In either case, there are two load-sharing power supplies that install into the bays located at the bottom rear of the chassis, as shown in
Figure 2. As viewed from the rear of the chassis, the supply on the left is referred to as supply
A and the supply on the right as supply B. The power supplies connect to the backplane, which distributes power to router components according to their individual voltage requirements. Each power supply has a system ground connector and an integrated fan to cool the power assembly.
.
The power supplies are fully redundant. When both power supplies are operational, they automatically share the electrical load. If one power supply stops functioning for any reason, the remaining power supply instantly begins providing all the power the router needs for normal functioning, and can provide full power indefinitely.
Power supplies are hot-removable and hot-insertable, as described in “Field-Replaceable
Units (FRUs)” on page 4. Each power supply has a safety interlock lever that prevents removal of the supply while it is on, but to avoid electrical injury, carefully follow the instructions in “Replace an AC Power Supply” on page 136 and “Replace a DC Power Supply” on page 141.
After powering off a power supply, wait at least 60 seconds before turning it back on. After powering on a power supply, wait at least 60 seconds before turning it off.
If the router is completely powered down when you power on a power supply, the Routing Engine boots as the power supply completes its startup sequence. If the Routing
Engine finishes booting and you need to power down the router again, first issue the CLI request system halt command.
After a power supply is powered on, it can take up to 60 seconds for status indicators—such as LEDs on the power supply, show chassis commands, and messages on the craft interface LCD—to indicate that the power supply is functioning normally. Ignore error indicators that appear during the first 60 seconds.
Power Supplies
AC Power Supply
An AC-powered router has two load-sharing AC power supplies, located at the bottom rear of
the chassis, as shown in Figure 2. Figure 8 shows the power supply and Table 8 lists electrical
specifications. For information about the LEDs on the power supply, see “Power Supply
Figure 8: AC Power Supply
For information about the cables required for each type of power supply, see “Power System
Requirements and Specifications” on page 44.
See the following sections for further information about the power supplies:
Captive screw
Handle
Extractor/inserter
Power switch
Appliance inlet
Safety interlock lever
Status LEDs
Grounding points
Table 8: AC Power Supply Electrical Specifications
Description
Maximum power outpu t
Input voltage
Input line frequency
Input current rating
Output voltage
Specification
1500 W
180–264 VAC operating range
50–60 Hz, autoranging
8A @ 208V
+3.3V, +5V, +2.5V, +12V, +24V
Hardware Component Overview
21
Power Supplies
DC Power Supply
A DC-powered router has two load-sharing DC power supplies, located at the bottom rear of
LEDs on the power supply, see “Power Supply LEDs” on page 22.
Figure 9: DC Power Supply
Handle Extractor/inserter
Captive screw
Power terminals
Power switch
Status LEDs
Safety interlock lever
Grounding studs
Table 9: DC Power Supply Electrical Specifications
Description
Maximum power output
Input voltage
Input current rating
Output voltage
Specification
1500 W
–40 through –75 VDC operating range
35A @ 48V
+3.3V, +5V, +2.5V, +12V, +24V
Power Supply LEDs
Table 10 describes the LEDs on both AC and DC power supplies.
Table 10: States for Power Supply LEDs
Label Color State
OK Green On steadily
Description
Power supply is functioning normally, input is occurring, outputs are within range, temperature is within range, and fans are operational.
FAIL Red On steadily Power supply has failed.
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M40 Internet Router Hardware Guide
Cooling System
Cooling System
The cooling system consists of separate subsystems (sets of fans and impellers) that draw room air into the chassis to keep its internal temperature below a maximum acceptable level.
When the temperature is below the maximum, the fans and impellers function at less than full speed. If sensors detect that the temperature of a component has exceeded the acceptable maximum—for example, because an impeller is removed—the speed of the remaining impellers and fans is automatically increased to reduce the temperature. The fans and impellers can function at the higher speed indefinitely.
For more information about the cooling system, see the following sections:
Cooling System Components on page 23
Airflow through the Chassis on page 24
Cooling System Components
The cooling system has the following components. Except as noted, they are hot-removable and hot-insertable, as described in “Field-Replaceable Units (FRUs)” on page 4.
Air intake vent and air filter—Provide an opening for room air to enter the router. They are located at the bottom of the chassis front, below the craft interface, as shown in
Figure 1. The air filter prevents dust and other particles from entering the cooling
system. For replacement instructions, see “Maintain and Replace the Air Filter” on page 154.
Do not remove the air filter for more than a minute or so while the router is operating. The fans and impellers are powerful enough to draw in foreign material, such as bits of wire, through the unfiltered air intake, which could damage router components.
Upper and lower impeller assemblies—Cool the Packet Forwarding Engine components
(backplane, SCB, FPCs, and PICs). The lower impeller assembly is located behind the craft interface at the front the chassis, and the upper assembly is located above the fan tray at the rear of the chassis. Each assembly houses two impellers for redundancy. The assemblies are not interchangeable. For replacement instructions, see “Replace the
Lower Impeller Assembly” on page 158 and “Replace the Upper Impeller Assembly” on page 159.
Fan tray—Cools the Routing Engine and backplane. The tray houses three fans for redundancy and is located above the Routing Engine at the upper rear of the chassis (see
Figure 2). For replacement instructions, see “Maintain and Replace the Fan Tray” on
page 155.
Power supply integrated fan—Cools the power supply. It is not field-replaceable.
Hardware Component Overview
23
Cable Management Sy stem
Airflow through the Chassis
Figure 10 shows airflow through the chassis and the location of the cooling subsystems.
Figure 10: Side View of Air Flow through the Chassis
Exhaust for
Packet Forwarding
Engine cooling
Exhaust for Routing
Engine and backplane cooling
Upper impellers
Fan tray
Routing
Engine
Rear of Chassis
Packet
Forwarding
Engine
Lower impellers
Exhaust for power supply
Power supply and Fans
Front of Chassis
Air intake for
Packet Forwarding
Engine cooling
Air intake for
Routing Engine cooling
Air intake for power supply cooling
Cable Management System
The cable management system is a row of staggered metal hooks located at the top of the
chassis front (see Figure 1). Each hook is draped with a rounded plastic shield and the row is
shielded by a removable cover. Threading PIC cables through the hooks keeps cables in place, reduces tangling, prevents undue stress on a cable by distributing its weight evenly, and helps maintain the proper bend radius for optical cables.
24
M40 Internet Router Hardware Guide
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