3Com 4007R Implementation Guide - Page 566

566 CHAPTER 22: QOS AND RSVP QoS Overview Quality of Service (QoS) is a Layer 3 feature that allows you to establish control over network traffic. QoS provides policy-based services, which establish various grades of network service to accommodate different types of traffic, such as multimedia, video, protocol-specific, time-critical, and file-backup traffic. Although QoS and Class of Service (CoS) are closely related, QoS has more features and addresses bandwidth, delay, loss, and jitter control. (CoS tends to focus on differentiating traffic into classes and assigning prioritization to those classes.) QoS is crucial in the wide area network (WAN) environment to guarantee quality of service without escalating WAN bandwidth costs. In the LAN environment, QoS implementations are growing. Features The Multilayer Switching Modules that are available on the Switch 4007 support the following QoS features: s QoS Classifiers - Define how the Multilayer Switching Module groups packets to schedule them with the appropriate service level. s QoS Controls - Assign rate limits and IEEE 802.1p priorities, as well as prioritize packets that are associated with one or more classifiers. Using the QoS Excess Tagging feature, you can also select an IEEE 802.1p priority for packets that exceed the control's rate limit. s Settable QoS Bandwidth - Controls the weighting of high-priority and best-effort traffic. s Resource Reservation Protocol (RSVP) - A building block of QoS that implements QoS characteristics in your LAN environment. RSVP is an end-to-end signaling IP protocol that allows an end station to request the reservation of bandwidth across the network. RSVP provides admission control. QoS can operate at Layer 2 and Layer 3; RSVP operates at Layer 3 only.