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M7i and M10i Packet Forwarding Engine Architecture

 

The Packet Forwarding Engine performs Layer 2 and Layer 3 packet switching. The Packet Forwarding Engine is implemented in application-specific integrated circuits (ASICs). It uses a centralized route lookup engine and shared memory.

Packet Forwarding Engine Components

The Packet Forwarding Engine architecture includes the following components:

  • Midplane—Transports packets, notifications, and other signals between the FPCs and the Packet Forwarding Engine (as well as other system components).

  • Physical Interface Card (PIC)—Physically connects the router to fiber-optic or digital network media. A controller ASIC in each PIC performs control functions specific to the PIC media type.

  • Compact Forwarding Engine Board (CFEB) or Enhanced Compact Forwarding Engine Board (CFEB-E)—Hosts an integrated ASIC, which makes forwarding decisions, distributes data cells to the shared memory, and directs data packets when they are ready for transmission.

Data Flow Through the Packet Forwarding Engine

Use of ASICs promotes efficient movement of data packets through the system. Packets flow through the Packet Forwarding Engine in the following sequence (see Figure 1):

  1. Packets arrive at an incoming networking interface.
  2. The networking interface passes the packets to the CFEB or CFEB-E, where the integrated ASIC processes the packet headers, divides the packets into 64-byte data cells, and distributes the data cells throughout the memory buffer.
  3. The integrated ASIC on the CFEB or CFEB-E performs a route lookup for each packet and decides how to forward it.
    1. If services are configured for the packet, the integrated ASIC reassembles the packet and passes them to the services interface.
    2. The services interface passes the packet to the CFEB or CFEB-E, where the integrated ASIC processes the packet, divides the packet into 64-byte cells, and distributes the data cells throughout the memory buffer.
    3. The integrated ASIC performs a second route lookup for each packet and decides how to forward it.
  4. The integrated ASIC notifies the outbound networking interface.
  5. The integrated ASIC reassembles data cells stored in shared memory into data packets as they are ready for transmission and passes them to the outbound networking interface.
  6. The outbound networking interface transmits the data packets.
Figure 1: Packet Forwarding Engine Components and Data Flow
Packet Forwarding Engine
Components and Data Flow