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DLSw Implementation Notes

304233-A Rev. 00

2-17

Nonordered Queues

Although Site Manager numbers the DLSw priority queues, the queue number

hierarchy does not determine priority. You configure both the number of queues

for each DLSw peer and the percentage of bandwidth assigned to each queue. For

example, you can assign 50 percent of available bandwidth to Q3 and 25 percent

each to Q1 and Q0.

The Dequeuing Process

The algorithm for DLSw bandwidth allocation is called weighted dequeuing. With

weighted dequeuing, packets at the front of the protocol prioritization queues

enter a dequeue list and receive a weighted score. Packets with the lowest score

are transmitted first.

By distributing the selection of packets from all queues, weighted dequeuing is

more stable than the algorithms used for circuit-level WAN protocol prioritization.

One goal of weighted dequeuing is to send smaller packets ahead of large packets,

without violating the bandwidth of each queue or depriving large packets. The

algorithm accomplishes this by putting smaller packets ahead of larger packets by

simultaneously considering how long the larger packets have been in the dequeue

list. A large packet accumulates credit (lowering its weighted score) as each

smaller packet gets ahead of it, and eventually the larger packet moves to the front

of the dequeue list.

The Dequeue List

Three factors determine a packet’s weighted score:

• Size of the packet

• Percent of bandwidth allocated to the packet’s queue

• Time spent in the dequeue list

The dequeuing algorithm calculates a packet’s dequeue weight using the

following formula:

Weight =

Size of packet

Bandwidth %

- Time in dequeue list

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Avaya Configuring DLSw Services Manual do Utilizador Página 73