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Queuing and Memory Interface ASICs

The Queuing and Memory Interface ASICs pass the data cells to memory for buffering. The data cells are placed into a queue to await transmission on the physical media. The specific queue used by the ASICs is determined by the forwarding class associated with the data packet. The configuration of the queue itself helps determine the service the packet receives while in this queued state. This functionality guarantees that certain packets will be serviced and transmitted before other packets. In addition, the queue settings and the packet’s loss priority setting determine which packets might be dropped from the network during periods of congestion.

In addition to queuing the packet, the outgoing I/O Manager ASIC is responsible for ensuring that CoS bits in the packet’s header are correctly set before it is transmitted. This rewrite function helps the next downstream router perform its CoS function in the network.

The Queuing and Memory Interface ASIC sends the notification to the Switch Interface ASIC facing the switch fabric, unless the destination is on the same Packet Forwarding Engine. In this case, the notification is sent back to the Switch Interface ASIC facing the outgoing ports, and the packets are sent to the outgoing port without passing through the switch fabric. The default behavior is for fabric priority queuing on egress interfaces to match the scheduling priority you assign. High-priority egress traffic is automatically assigned to high-priority fabric queues.

The Queuing and Memory Interface ASIC forwards the notification, including next-hop information, to the outgoing Switch Interface ASIC.

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