JUNOS Internet Software Network Operations Guide: Hardware
98 ! Understanding Key Router Components
Data Flow Through the M40 Router Packet Forwarding Engine
Data flows through the M40 router Packet Forwarding Engine in the sequence
shown in Figure 17.
Figure 17: M40 Router Packet Forwarding Engine Components and Data Flow
1. Packets arrive at an incoming PIC interface.
2. The PIC passes the packets to the FPC, where the I/O Manager ASIC processes
the packet headers, divides the packets into 64-byte data cells, and passes the
cells to the backplane.
3. The Distributed Buffer Manager ASIC on the backplane distributes the data cells
throughout the memory buffers located on and shared by all the FPCs.
4. The Internet Processor or Internet Processor II ASIC on the SCB performs route
lookups and makes forwarding decisions.
5. The Internet Processor or Internet Processor II ASIC notifies a second
Distributed Buffer Manager ASIC on the backplane of the routing decision.
6. The Distributed Buffer Manager ASIC forwards the notification to the FPC that
hosts the outbound PIC.
7. The I/O Manager ASIC on the FPC reassembles data cells in shared memory
into data packets as they are ready for transmission and passes them to the
outbound PIC.
8. The outbound PIC transmits the data packets.
Routing Engine
Backplane
System Control
Board
Internet
Processor
1243a
= ASIC
Packet
in
Packet
out
PIC PIC
FPC
FPC
I/O
manager
I/O
manager
Distributed Buffer
Manager
ControllerController
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