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Configuring Virtual Circuit CoS Mode on ATM Interfaces

Virtual Circuit (VC) CoS mode defines the CoS queue scheduling priority. By default, the VC CoS mode is alternate. When it is a queue’s turn to transmit, the queue transmits up to its weight in cells as specified by the transmit-weight statement at the [edit interfaces at-fpc/pic/port atm-options scheduler-maps map-name forwarding-class class-name] hierarchy level. The number of cells transmitted can be slightly over the configured or default transmit weight, because the transmission always ends at a packet boundary.

To configure the VC CoS mode, include the vc-cos-mode statement at the [edit interfaces at-fpc/pic/port atm-options scheduler-maps] hierarchy level:

Two modes of CoS scheduling priority are supported:

  • alternate—Assign high priority to one queue. The scheduling of the queues alternates between the high priority queue and the remaining queues. Every other scheduled packet is from the high priority queue.

  • strict—Assign strictly high priority to one queue. A queue with strictly high priority is always scheduled before the remaining queues. The remaining queues are scheduled in round-robin fashion.