TABLE OF CONTENTS In networking, the term quality of service (QOS) can mean many different things to different people, hence it is key that we start this chapter by defining what "QOS" means in the context of this book.
Firstly, how do we define a "service" in the context of IP networking? We consider that a service is a description of the overall treatment of a customer's traffic across a particular domain. A service is only practically useful if it meets the requirements of the end-user applications it is intended to support. Hence, the aim of the service is to maximize end-user satisfaction with the applications that the service is supporting. Maximizing user satisfaction requires that the end-user applications work effectively.
How then do we define "quality" in the context of a particular IP service? We can define service quality in terms of the underlying requirements for an application which can be defined in terms of the SLA metrics for IP service performance defined in Chapter 1: delay, jitter, packet loss, throughput, service availability, and per flow sequence preservation.
QOS, however, implies more than just ensuring that a network service is able to support the SLA requirements of the applications it is aiming to support. The problem of ensuring that a network can meet these requirements is fundamentally a problem of managing the available network capacity relative to the service load, i.e. a problem of managing congestion. If it is possible to ensure that there is always...
