Understanding Key Router Components ! 97
Chapter 12: Monitoring Key Router Components
Data Flow Through the M20 Router Packet Forwarding Engine
Data flows through the M20 router Packet Forwarding Engine in the sequence
shown in Figure 16.
Figure 16: M20 Router Packet Forwarding Engine Components and Data Flow
1. Packets arrive at an incoming PIC interface.
2. The I/O Manager ASIC processes the packet headers, divides the packets into
64-byte data cells, and passes the cells through the midplane to the SSB.
3. A Distributed Buffer Manager ASIC on the SSB distributes the data cells
throughout the memory buffers located on and shared by all the FPCs.
4. The Internet Processor II ASIC on the SSB performs a route lookup for each
packet and decides how to forward it.
5. The Internet Processor II ASIC notifies a Distributed Buffer Manager ASIC on
the SSB of the forwarding decision, and the Distributed Buffer Manager ASIC
forwards the notification to the FPC that hosts the appropriate outbound
interface.
6. The I/O Manager ASIC on the FPC reassembles data cells stored in shared
memory into data packets as they are ready for transmission and passes them
through the Packet Director ASIC to the outbound PIC.
7. The outbound PIC transmits the data packets.
Routing Engine
Midplane
SSB
Internet
Processor
1243
= ASIC
Packet
in
Packet
out
PIC PIC
FPC
FPC
I/O
Manager
I/O
Manager
Distributed Buffer
Manager
ControllerController
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