Cabletron Systems 9032578-05 manual Chapter QoS Configuration Guide

Chapter 21

QoS Configuration

Guide

QoS & Layer-2/Layer-3/Layer-4 Flow Overview

The SSR allows network managers to identify traffic and set Quality of Service (QoS) policies without compromising wire speed performance. The SSR can guarantee bandwidth on an application by application basis, thus accommodating high-priority traffic even during peak periods of usage. QoS policies can be broad enough to encompass all the applications in the network, or relate specifically to a single host-to-host application flow.

The SSR provides four different features to satisfy QoS requirements:

•Traffic prioritization allows network administrators to identify and segregate mission- critical network traffic into different priority queues from non-critical network traffic. Once a packet has been identified, it can be assigned into any one of four priority queues in order to ensure delivery. Priority can be allocated based on any combination of Layer-2, Layer-3, or Layer-4 traffic.

•Weighted Random Early Detection (WRED) alleviates traffic congestion by randomly dropping packets before the queue becomes completely flooded. WRED should only be applied to TCP traffic.

•Type of Service (ToS) rewrite provides network administrators access to the ToS octet in an IP packet. The ToS octet is designed to provide feedback to the upper layer application. The administrator can “mark” packets using the ToS rewrite feature so that the application (a routing protocol, for example) can handle the packet based on a predefined mechanism.

•Traffic rate limiting provides network administrators with tools to manage bandwidth resources. The administrator can create an upper limit for a traffic profile, which is based on Layer-3 or Layer-4 information. Traffic that exceeds the upper limit of the profile can either be dropped or re prioritized into another priority queue.

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