Cisco WS-C4003 Software Guide - Page 223

Configuring QoS 14 C H A P T E R This chapter describes how to configure quality of service (QoS) on the Catalyst enterprise LAN switches. Note For complete syntax and usage information for the commands used in this chapter, refer to the Command Reference-Catalyst 4000 Family, Catalyst 2948G, and Catalyst 2980G Switches. This chapter consists of these sections: • Understanding How QoS Works, page 14-1 • Software Requirements, page 14-4 • QoS Default Configuration, page 14-4 • Configuring QoS, page 14-4 Understanding How QoS Works These sections describe how QoS works: • Overview of QoS, page 14-1 • QoS Terminology, page 14-2 • Understanding Classification and Marking at the Ingress Port, page 14-3 • Understanding Scheduling, page 14-3 Overview of QoS Typically, networks operate on a best-effort delivery basis, which means that all traffic has equal priority and an equal chance of being delivered in a timely manner. When congestion occurs, all traffic has an equal chance of being dropped. QoS selects network traffic, prioritizes it according to its relative importance, and provides priority-indexed treatment through congestion-avoidance techniques. Implementing QoS in your network makes network performance more predictable and bandwidth utilization more effective. QoS classifies traffic by assigning priority-indexed 802.1p class of service (CoS) values to frames at ingress ports. If traffic is tagged with a CoS vlaue at the ingress port, the switch forwards the value. If traffic is native, then the switch can rewrite the CoS tag. 78-12647-02 Software Configuration Guide-Catalyst 4000 Family, Catalyst 2948G, Catalyst 2980G, Releases 6.3 and 6.4 14-1