Case Study: Quality of Service Processing in The Cisco Catalyst 6000 and 6500 Series Switches

The key quality of service (QoS) functions in the Catalyst 6000/6500 family of switch/routers requiring real‐time processing is implemented in hardware. These QoS‐related hardware components are implemented on Catalyst 6000/6500 modules such as the Policy Feature Card (PFC) and the port ASICs on the line cards. This chapter describes the QoS capabilities of the PFC and the switch/router port ASICs on the line cards. The Multilayer Switch Feature Card (MSFC) supports some QoS functions such as control plane policing and other rate‐limiting functions for control and management traffic. The Distributed Forwarding Card (DFC) allows fabric‐enabled and fabric‐only line cards to perform packet forwarding and QoS processing locally without direct MSFC intervention. To facilitate the application of QoS services to traffic passing through the switch/router, mechanisms to tag or prioritize IP packets or Ethernet frames are required. The chapter also describes the various QoS operations that are applied to a packet as it transits the switch/router.