Data Flow Through the Packet Forwarding Engine

You can understand the function of the Packet Forwarding Engine by following the flow of a packet through the router: first into a PIC, then through the switching fabric, and finally out another PIC for transmission on a network link. Generally, the data flows through the Packet Forwarding Engine as follows:

1. Packets enter the router through incoming PIC interfaces, which contain controllers that perform media-specific processing.
2. The PICs pass the packets to the FPCs, where they are divided into cells and are distributed to the router’s buffer memory.
3. The Packet Forwarding Engine performs route lookups, forwards the notification to the destination port, reassembles the cells into packets, and sends them to the destination port on the outgoing PIC.
4. The PIC performs encapsulation and other media-specific processing, and sends the packets out into the network.