User`s guide

XSR User’s Guide 209
10
Configuring Quality of Service
Overview
In a typical network, there are often many users and applications competing
for limited system and network resources. While resource sharing on a first-
come, first-serve basis may suffice when your network load is light, access
can freeze quickly when the network gets congested. Under these conditions,
a bandwidth-hungry application (large file transfer files, emails) may devour
most of the network bandwidth, depriving applications that send small-sized
packets (voice, telnet and other interactive applications) of their fair share of
bandwidth, and result in long delays causing applications to fail.
Quality of Service cannot magically provide all applications their requested
bandwidth, but it can help you identify your mission-critical, high priority
application traffic and give it preferential treatment (higher priority, higher
bandwidth or guaranteed bandwidth) relative to the rest of your network
traffic. In this way, critical applications will work under both normal and
congested conditions while less important and time-sensitive traffic will
continue to flow, perhaps at a lower rate than expected.
To configure QoS properly, you should consider the following:
 Know the load on your network to decide if you need QoS processing
 Know the programs running on your network to identify vital
applications that you need to protect, and determine how much
bandwidth you need to allocate to these applications
 Determine how to classify traffic into different classes
 Decide which queueing algorithms, congestion mechanisms, and
traffic options best satisfy your overall applications
 Configure the XSR using the above criteria