Dell 28XX manual Dscp Value Forwarding Queue Values, CoS Services, 145

DSCP values can be mapped to priority queues. The following table contains the default DSCP mapping to forwarding queue values:

Table 9-2. DSCP to Queue Mapping Table Default Values

DSCP Value	Forwarding Queue Values
0-	q1
	q2
	q3
	q4

DSCP mapping is enabled on a per-system basis.

CoS Services

After packets are assigned to a specific queue, CoS services can be assigned to the queue(s). Output queues are configured with a scheduling scheme by one of the following methods:

•Strict Priority — Ensures that time-sensitive applications are always forwarded through an expedited path. Strict Priority allows the prioritization of mission-critical, time-sensitive traffic over less time- sensitive applications.

For example, under Strict Priority, voice over IP traffic is forwarded before FTP or e-mail (SMTP) traffic.

The strict priority queue is emptied before the traffic in the remaining queues is forwarded.

•Weighted Round Robin — Ensures that a single application does not dominate the device forwarding capacity. Weighted Round Robin (WRR) forwards entire queues in a Round Robin order. Queue priorities are defined by the queue length. The longer the queue length, the higher the queue's forwarding priority.

For example, if queues have queue weights of , packets with the highest forwarding priority are assigned to queue , and packets with the lowest forwarding priority assigned to queue .

By providing highest forwarding priorit queues, WRR processes higher priority traffic, and ensures that low-priority traffic is forwarded satisfactorily.

The scheduling scheme is enabled system-wide. Queues assigned to the strict priority policy are automatically assigned to the highest priority queue. By default, all values are set as Strict Priority. Queue weight values can be assigned in any order using WRR, and WRR values can be assigned system-wide. Best effort traffic is always assigned to the first queue.

Dell PowerConnect 28xx Systems User Guide

145