Transition Networks
S4224 Web User Guide
33558 Rev. C
Page 323 of 669
6 Queues Weighted (Deficit Weighted Round Robin)
The DWRR uses a cost-based algorithm (compared to a weight-based algorithm). A high cost implies a
small share of the bandwidth. When DWRR is enabled, each of the queues 5 through 0) are programmed
with a cost (a number from 1 - 32). The programmable DWRR costs determine the behavior of the DWRR
algorithm. The costs result in weights for each queue. The weights are relative to one another, and the
resulting share of the egress bandwidth for a particular QoS class is equal to the queue’s weight divided
by the sum of all the queues’ weights.
Costs can be converted to weights (and vice versa) with these two algorithms:
Weight to Cost
: given a desired set of weights (W0, W1, W2, W3, W4, W5), calculate the costs using the
following algorithm:
1. Set the cost of the queue with the smallest weight (
Wsmallest
) to cost 32.
2. For any other queue Qn with weight Wn, set the corresponding cost Cn to
Cn = 32 x Wsmallest / Wn
.
Cost to Weight
: given a set of costs for all queues (C0, C1, C2, C3, C4, C5), then calculate the resulting
weights using the following algorithm:
1. Set the weight of the queue with the highest cost (
Chighest
) to 1.
2. For any other queue Qn with cost Cn, set the corresponding weight Wn to
Wn = Chighest / Cn
.
The
Configuration
>
QoS
>
Port Scheduler
menu path provides an overview of QoS Egress Port
Schedulers for all S4224 ports.
The displayed QoS Egress Port Schedulers settings are described below.
Port
The logical port for the settings contained in the same row. Click on the port number in order to
configure the schedulers.
Mode
Shows the scheduling mode for this port (“Strict Priority” or “Weighted”). Generally, Strict Priority (SP)
queues are scheduled before WRR queues.
Strict Priority
-
The port transmits all packets out of higher priority queues before transmitting
any from the lower priority queues.
Weighted
- (WRR or Weighted Round Robin) - The port transmits a set number of packets from
each queue, in a round robin fashion, so that each has a chance to transmit traffic.
Weight (Q0 - Q5)
Shows the weight for this queue (Q0-Q5) and port (port 1-6).
WRR setting examples for the number of packets transmitted from each queue are shown below.
These values are permanent and you cannot change them.
Port Egress Queue
Max. No. of Packets
Q3
8
Q2
4
Q1
2
Q0
1
