Datasheet

Hardware Component Overview

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.