Fig. 7.12 Deficit Weighted Round Robin - SMC Networks 7824M/VSW - annexe 1 Manual

Management Guide
TigerAccess™ EE
SMC7824M/VSW
Deficit Weighted Round Robin (DWRR)
Deficit Weighted Round Robin (DWRR) combines the advantages of DRR and WRR
scheduling algorithms. Processing the packets that have higher priority is the same way
as strict priority queuing. DWRR provides differentiated service because it processes
packets as much as weight. The specific packet length is assigned to each queue by dif-
ferent weight as the unit of byte. Each queue transmits different packets within packet
length up to (256 bytes x configured weight) bytes in one round.
DWRR transmits from the queues without starving the low-priority queue, because each
queue can be assigned with different weight. DWRR scheduling algorithm keeps the re-
mainder of packet length from previous round and compensates for it in the next round. If
a queue is not able to send a packet because its packet size is larger than the available
bytes, then the unused bytes are credited to the next round.
Fig. 7.12 Deficit Weighted Round Robin
Different queues have different weights, and the packet length assigned to each queue in
its round is proportional to the relative weight of the queue among all the queues serviced
by that scheduler.
The queue of number 7 has 3 weights, handles the packet length of 768 bytes at once in
its round. If the queue of number 7 was not able to send all packets in its previous round
because its last packet size was too large, the remainder of 128 bytes from is added to
the packet length for the next round. Therefore, the queue of number 7 can send the
packets up to 896 bytes of length in its next round.
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