Specifications

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§ PICs—One to four PICs can be attached to each FPC. PICs provide
support for various network media, including OC-12 ATM, OC-48
SONET, Gigabit Ethernet, and DS3.
Midplane
The router midplane forms the back of the card cage. The FPCs, SSB, and craft
interface install into the midplane from the front of the chassis. Fan trays plug into
the midplane from both the front and rear of the chassis. Power supplies and the
Routing Engine plug into the midplane from the back of the chassis. The
midplane is a component of the Packet Forwarding Engine. It is responsible for
power distribution and signal connectivity. The router power supplies are
connected to the midplane, which distributes power and provides signal
connectivity to all the FPCs, the SSB, and other system components.
System and Switch Board (SSB)
The SSB occupies the top slot of the card cage, installing into the midplane from
the front of the chassis. The SSB houses the Internet Processor ASIC and two
Distributed Buffer Manager ASICs. The SSB communicates with the Routing
Engine using a dedicated 100-Mbps Fast Ethernet link that transfers routing table
data from the Routing Engine to the forwarding table in the Internet Processor
ASIC. The link is also used to transfer from the SSB to the Routing Engine
routing link-state updates and other packets destined for the router that have
been received through the router interfaces.
The SSB is a component of the Packet Forwarding Engine and performs the
following major functions:
§ Management of shared memory on the FPCs—The Distributed Buffer
Manager ASIC on the SSB 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 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 the synchronous
SRAM (SSRAM). After performing the lookup, the Internet Processor
ASIC informs the midplane of the forwarding decision, and the midplane
forwards the decision on to the appropriate outgoing interface.
§ Monitoring system components—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.
§ Transferring exception and control packets—The Internet Processor
ASIC passes exception packets to a microprocessor on the SSB, which
processes almost all of them. The remainder 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 syslog messages.
§ Controlling FPC resets—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.
The SSB is hot-insertable and hot-removable. You can remove and replace the
SSB without powering down the router, but doing so interrupts packet fowarding.
SSB Components
The SSB contains the following components:
§ Processing components
o 200-MHz CPU and supporting logic
o Internet Processor ASIC
o Distributed Buffer Manager ASICs