442 Configuring Quality of ServicePackets arriving untagged are assigned a default VPT value, which is set on a per port basis. The assignedVPT 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 mappingto egress queue values:DSCP mapping is enabled on a per-system basis.This section contians the following topics:• "CoS Services" on page 442CoS ServicesAfter packets are assigned to a specific egress queue, CoS services can be assigned to the queue(s).Egress queues 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 forwardedbefore FTP or e-mail (SMTP) traffic.• Weighted Round Robin — Ensures that a single application does not dominate the device forwardingcapacity. Weighted Round Robin (WRR) forwards entire queues in a Round Robin order. All queuescan be configured to WRR or SP queues. If WRR is selected, the following weights are assigned to thequeues: 1, 2, 4, 8.5 q36 q47 q4Table 9-2. DSCP to Queue Mapping Table Default ValuesDSCP Value Forwarding Queue Va lues0-15 q1 (Lowest Priority)16-31 q232-47 q348-63 q4Table 9-1. CoS to Queue Mapping Table Default values (continued)CoS Value Forwarding Queue Values
