M160 Internet Router Hardware Guide
The SFM communicates with the RoutingEngine using a dedicated 100-Mbps Fast
Ethernet link that transfers routingtable data from the Routing Engine to the
forwarding tablein the InternetProcessor II ASIC. The link is also used to transfer
from the SFM tothe Routing Engine routing link-state updatesand other packets
destined for the routerthat have been received through the router interfaces.
The ASICs and othercomponents on the SFM provide the followingfunctions:
Route lookups—The Internet ProcessorII ASIC on each SFM performs route
lookups using the forwardingtable stored in SSRAM.
Management of sharedmemory on the FPCs—One Distributed Buffer Manager
ASIC receives the 64-byte data cells into which the I/O Manager ASICs on each
FPC divide incoming packets,and uniformly allocates them throughout the
shared memory buffers located on the FPCs.
Transferof outgoing data packets—The second Distributed Buffer Manager
ASIC passes notification of theforwarding decision for each packet to an I/O
Manager ASIC so that data cellsfor the outgoing packet can be reassembled
for transmission to the network.
Transferof exception and control packets—The Internet Processor II ASIC
passes exceptionpackets to the microprocessor on the SFM, which processes
almost all of them. The SFM sends any remaining exception packets to
the Routing Engine forfurther processing. When the SFM detectsan error
originating in the PacketForwarding Engine, it sends it to the Routing Engine
using system logging (syslog)messages.
SFM Components
EachSFMisatwo-boardsystem,asshowninFigure8. Ithas
the following components:
TwoDistributed Buffer Manager ASICs—Process incoming and outgoing
packets: one distributes data cells (which the I/O Manager ASIC on each
FPC derives from incoming packets)to the shared memory buffers on the
20 Packet Forwarding Engine