Sfm Components - Juniper Internet Router M160 Hardware Manual

M160 Internet Router Hardware Guide
The SFM 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 II ASIC. The link is also used to transfer
from the SFM to the Routing Engine routing link-state updates and other packets
destined for the router that have been received through the router interfaces.
The ASICs and other components on the SFM provide the following functions:

SFM Components

Each SFM is a two-board system, as shown in Figure 8. It has
the following components:
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Packet Forwarding Engine
Route lookups—The Internet Processor II ASIC on each SFM performs route
lookups using the forwarding table stored in SSRAM.
Management of shared memory 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.
Transfer of outgoing data packets—The second Distributed Buffer Manager
ASIC passes notification of the forwarding decision for each packet to an I/O
Manager ASIC so that data cells for the outgoing packet can be reassembled
for transmission to the network.
Transfer of exception and control packets—The Internet Processor II ASIC
passes exception packets to the microprocessor on the SFM, which processes
almost all of them. The SFM sends any remaining exception packets to
the Routing Engine for further processing. When the SFM detects an error
originating in the Packet Forwarding Engine, it sends it to the Routing Engine
using system logging (syslog) messages.
Two Distributed 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