In this chapter you learned about quality of service and why it is becoming more important for many. With the advent of voice and video convergence, QoS is now required end-to-end on all network devices between application end points. This includes not only Layer 3 routers, but also LAN switches. The LAN switch is a key component of an end-to-end QoS design; the LAN switch is the first device that receives traffic that requires a particular QoS level. In a DiffServ QoS implementation, where QoS for traffic is indicated within each frame or packet, marking is required at the network entry point to ensure end-to-end QoS. Cisco Catalyst switches allow seamless integration of QoS between Layer 2 and Layer 3 networks, reducing the cost and complexity of providing end-to-end QoS.
QoS is provided on Cisco Catalyst switches through the implementation of key QoS functions, such as classification and marking at the ingress, policing at the ingress or egress, and queuing and scheduling at the egress. Cisco Catalyst switches support the use of 802.1p class of service, IP Precedence, and DiffServ Code Point (DSCP) markings, with the ability to trust or override existing QoS markings. Cisco has recently invested much research and development into providing advanced QoS features, the benefits of which are now available on the next generation of Cisco Catalyst switches. Even switches at the workgroup level can classify traffic based upon Layer 3 or 4 parameters and support next-generation QoS features such as DSCP. You need to be aware of the differences in QoS support between each Catalyst platform and understand that the configuration syntax for QoS also varies.