Cos Services; Dscp To Queue Mapping Table Default Values - Dell PowerConnect 5324 User Manual

Packets arriving untagged are assigned a default VPT that is set on a per port basis. The assigned
VPT is used to map the packet to the output queue and as the egress VPT.
DSCP values can be mapped to priority queues. The following table contains the default DSCP
mapping to forwarding queue values:
Table 9-93. DSCP to Queue Mapping Table Default Values
DSCP Value
0-7
8-15
16-23
24-31
32-39
40-47
48-55
55-63
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). Out-
put 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 in 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 four queues have queue weights of 1, 2, 3 and 4, packets with the highest
forwarding priority are assigned to queue 4, and packets with the lowest forwarding priority
assigned to queue 1.
By providing highest forwarding priority to length 4 queues, weighted round robin processes
higher priority traffic, and ensure 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.
Forwarding Queue Values
q2 (Lowest Priority)
q1
q1
q2
q3
q3
q4
q4 (Highest Priority)
Configuring Quality of Service
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