Nortel-networks NB5PLUS4/W Manual do Utilizador descarregar pdf (Página 46)

NB5Plus4/W User Guide YML754Rev1

46 www.netcomm.com.au

The Medium and Low priority queue lengths will be proportionally calculated via the

queue weights selected in 1.) Queue Priorities above.

Total queue length for all three queues will sum to the transmit queue length set in

the system.

Packets overowing their queues will be tail-dropped, penalizing stochastically the

greediest ow within each queue.

Future implementations may introduce a “buffer stealing” policy. This policy will re-

move the xed buffer limits and allow a particular queue buffer to decrease to some

predened minimum limit.

De-queuing Policy

Expedited Forwarding Queue (High Priority) is always serviced rst at each packet

scheduling cycle and serviced to extinction. Therefore, the EF queue is non-preemti-

ble by the Medium and Low priority queues.

WRR Queue Scheduler for Medium and Low priority queues

The L and M weights will be congured from the Web UI as stated above in 1.)

Queue Priorities.

A service scheduling array will be pre-computed for the Medium and Low priority

queues based on the user congurable weights assigned to these queues. Each ar-

ray slot corresponds to a scheduling cycle. The pre-computed algorithm will allo-

cate scheduling slots for each queue based on the Medium and Low priority queue

weights and uniformly interleave them through the scheduling array. This array will

provide an O(1) scheduler with a minimum possible average latency for each of the

two queues.

Configuration:

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Nortel-networks NB5PLUS4/W Manual do Utilizador Página 46