Configuring Quality of Service 421Configuring Quality of ServiceThe Quality of Service page contains links to the main QoS configuration pages. To open the page,click Quality of Service in the tree view.Quality of Service OverviewNetwork traffic is usually unpredictable, and the only basic assurance that a network administratorcan offer is best effort traffic delivery. To overcome this challenge, network administrators applyQuality of Service (QoS) throughout the network. This ensures that network traffic is prioritizedaccording to specified criteria, and that specific traffic receives preferential treatment. QoS in thenetwork optimizes network performance and entails two basic facilities:• Classifying incoming traffic into handling classes, based on an attribute, including:– The ingress interface– Packet content– A combination of these attributes• Providing various mechanisms for determining the allocation of network resources todifferent handling classes, including:– The assignment of network traffic to a particular hardware queue– The assignment of internal resources– Traffic shapingIn this document, the terms Class of Service (CoS) and QoS are used in the following context:• CoS provides varying Layer 2 traffic services. CoS refers to classification of traffic to traffic-classes, which are handled as an aggregate whole, with no per-flow settings. CoS is usuallyrelated to the 802.1p service that classifies flows according to their Layer 2 priority, as set inthe VLAN header.• QoS refers to Layer 2 traffic and above. QoS handles per-flow settings, even within a singletraffic class.The QoS facility involves the following elements:• Access Control Lists (ACLs) — Used to decide which traffic is allowed to enter the system,and which is to be dropped. Only traffic that meets this criteria are subject to CoS or QoSsettings. ACLs are used in QoS and network security.• Traffic Classification — Classifies each incoming packet as belonging to a given traffic class,based on the packet contents and/or the context.
