Queue mode – Microsens MS453490M Management Guide User Manual

Page 818

HAPTER

| Class of Service Commands

Priority Commands (Layer 2)

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queue mode

This command sets the scheduling mode used for processing each of the

class of service (CoS) priority queues. The options include strict priority,

Shaped Deficiit Weighted Round-Robin (SDWRR), or a combination of strict

and weighted queuing. Use the no form to restore the default value.

YNTAX

queue mode {strict | wrr | strict-wrr [queue-type-list]}
no queue mode

strict - Services the egress queues in sequential order, transmitting

all traffic in the higher priority queues before servicing lower priority

queues. This ensures that the highest priority packets are always

serviced first, ahead of all other traffic.
wrr - Shaped Deficit Weighted Round-Robin shares bandwidth at

the egress ports by using scheduling weights (based on the

queue

weight

command), and servicing each queue in a round-robin

fashion.
strict-wrr - Strict priority is used for the high-priority queues and

SDWRR for the rest of the queues.
queue-type-list - Indicates if the queue is a normal or strict type.

(Options: 0 indicates a normal queue, 1 indicates a strict queue)

EFAULT

ETTING

Strict and WRR, with Queue 3 using strict mode

OMMAND

ODE

Global Configuration

OMMAND

SAGE

◆

The switch can be set to service the port queues based on strict

priority, SDWRR, or a combination of strict and weighted queueing.

◆

Strict priority requires all traffic in a higher priority queue to be

processed before lower priority queues are serviced.

◆

The SDWRR algorithm used by this switch is known as Shaped Deficit

Weighted Round Robin (SDWRR).

The basic WRR algorithm uses a relative weight for each queue that

determines the percentage of service time the switch services each

queue before moving on to the next queue. This prevents the head-of-

line blocking that can occur with strict priority queuing.

Deficit Weighted Round-Robin (DWRR) services the queues in a manner

similar to WRR, but the next queue is serviced only when the queue’s

Deficit Counter becomes smaller than the packet size to be transmitted.

As a result, traffic on queues with large weights cause increased latency

and jitter for traffic waiting for scheduling on other queues. In SDWRR,

if two or more queues have traffic eligible for transmission (i.e., the

Deficit Counter is greater than the packet size to be transmitted), then

a round-robin scheme among those queues is used, while still