Chapter 9. Quality of Service
To increase communications efficiency, both businesses and service providers are looking to IP-based networks to transport voice, video, and data services. Voice and video have special networking requirements, which IP networks must be able to provide. This means IP networking devices, such as local-area network (LAN) switches and routers require enhanced intelligence, with the ability to differentiate between various traffic types, identify applications such as voice or video, and provide the appropriate network resources as required.
A common question that is asked about quality of service (QoS) on the LAN is a simple onewhy? It is a simple yet valid question. Modern switched networks are high-speed networks that are more than capable of handling many organization's bandwidth requirements. With the recent push to converge voice and video onto the data network, QoS has moved from being a wide-area network (WAN)only feature (where the links are relatively slow) to a feature that is required throughout the WAN and LAN. Voice traffic is not bandwidth-hungry; it is delay and jitter-sensitive. A LAN must be able to provide minimal delay and jitter; it is these requirements that make QoS on the LAN a real requirement.
This chapter discusses quality of service (QoS), which in the context of network devices refers to the identification of a particular type of network traffic (that relates to a application or service) and the allocation of network resources to ensure the traffic gets the appropriate level of service from the network. The exciting topic of Cisco's IP Telephony offering is also introduced, with a discussion of how Cisco switches complement and enhance a Cisco IP Telephony network. The following topics are discussed: