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JUNOS Internet Software Network Operations Guide: Hardware

406 ! Understanding the SSB

Understanding the SSB

Purpose Inspect the SSB to ensure that it provides allocation of incoming data packets

throughout shared memory on the FPCs, transfers outgoing data cells to the FPCs

for packet reassembly, performs route lookups using the forwarding table, monitors

system components for failure and alarm conditions, and monitors FPC operation

and reset.

What Is the SSB The SSB is a component of the Packet Forwarding Engine and performs the

following major functions (see Figure 164 on page 407):

! Shared memory management on the FPCs—The Distributed Buffer Manager

application-specific integrated circuit (ASIC) on the SSB uniformly allocates

incoming data packets throughout shared memory on the FPCs.

! Outgoing data cell transfer to the FPCs—A second Distributed Buffer Manager

ASIC on the SSB passes data cells to the FPCs for packet reassembly when the

data is ready to be transmitted.

! Route lookups—The Internet Processor ASIC on the SSB performs route

lookups using the forwarding table stored in synchronous SRAM (SSRAM). After

performing the lookup, the Internet Processor ASIC informs the midplane of

the forwarding decision, and the midplane forwards the decision to the

appropriate outgoing interface.

! System component monitoring—The SSB monitors other system components

for failure and alarm conditions. It collects statistics from all sensors in the

system and relays them to the Routing Engine, which sets the appropriate

alarm. For example, if a temperature sensor exceeds the first internally defined

threshold, the Routing Engine issues a “high temp” alarm. If the sensor exceeds

the second threshold, the Routing Engine initiates a system shutdown.

! Exception and control packet transfer—The Internet Processor ASIC passes

exception packets to a microprocessor on the SSB, which processes almost all

of them. The remaining packets are sent to the Routing Engine for further

processing. Any errors originating in the Packet Forwarding Engine and

detected by the SSB are sent to the Routing Engine using system log messages.

! FPC reset control—The SSB monitors the operation of the FPCs. If it detects

errors in an FPC, the SSB attempts to reset the FPC. After three unsuccessful

resets, the SSB takes the FPC offline and informs the Routing Engine. Other

FPCs are unaffected, and normal system operation continues.

Brand	Juniper
Model	JUNOS - NETWORK OPERATION GUIDE REV1
Category	Software
Language	English

Juniper JUNOS - NETWORK OPERATION GUIDE REV1 User Manual

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