Cisco SLM248G Administration Guide - Page 50

Quality of Service 6 Quality of Service Network traffic is usually unpredictable, and the only basic assurance that can be offered is best effort traffic delivery. To overcome this challenge, Quality of Service (QoS) is applied throughout the network. This ensures that network traffic is prioritized according to specified criteria, and that specific traffic receives preferential treatment. QoS in the network 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 to different handling classes, including: - The assignment of network traffic to a particular hardware queue - The assignment of internal resources - Traffic shaping 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 usually related to the 802.1p service that classifies flows according to their Layer 2 priority, as set in the VLAN header. • QoS refers to Layer 2 traffic and above. QoS handles per-flow settings, even within a single traffic class. The QoS facility involves the following elements: • Traffic Classification - Classifies each incoming packet as belonging to a given traffic class, based on the packet contents. • Assignment to Hardware Queues - Assigns incoming packets to forwarding queues. Packets are sent to a particular queue for handling as a Cisco Small Business SLM Series Smart Switches Administration Guide 46