442 Configuring Quality of Service
Packets arriving untagged are assigned a default VPT value, which is set on a per port basis. Theassigned
VPT is used to map the packet to the egress queue.
DSCP values can be mapped to priority queues. The following table contains the default DSCP mapping
to egress queue values:
DSCP mapping is enabled on a per-system basis.
This section contians the following topics:
• "CoS Services" on page 442
CoS Services
After packets are assigned to a specific egress queue, CoS services can be assigned to the queue(s).
Egressqueues are configured with a scheduling scheme by one of the following methods:
•
Strict Priority
— Ensures that time-sensitive applications are always forwarded. Strict Priority (SP)
allows the prioritization of mission-critical, time-sensitive traffic over less time-sensitive applications.
For example, under Strict Priority, voice over IP traffic can be prioritized so the IP traffic is forwarded
before FTP or e-mail (SMTP) traffic.
•
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. All queues
can be configured to WRR or SP queues. If WRR is selected, the following weights are assigned to the
queues: 1, 2, 4, 8.
5q3
6q4
7q4
Table 9-2. DSCP to Queue Mapping Table Default Values
DSCP Value Forwarding Queue Values
0-15 q1 (Lowest Priority)
16-31 q2
32-47 q3
48-63 q4
Table 9-1. CoS to Queue Mapping Table Default values (continued)
CoS Value Forwarding Queue Values