Chapter 21. Quality of Service

In this chapter, we will introduce the quality of service (QoS) topic as applicable to IP communication scenarios. QoS is a complex topic, and we will describe in this chapter just some basic ideas that allow the reader to understand the mechanisms and protocols that exist to provide quality of service.

We will start by looking at some of the available architectures at the IP transport level to provide QoS, such as integrated services and differentiated services. Then we will introduce the framework for policy control, which enables the introduction of more intelligence in the admission control decisions for QoS. Then we will see how these ideas are applied in a SIP-based communication scenario and what the necessary SIP extensions are in order to integrate the SIP/SDP session establishment process with the underlying IP transport-level processes for quality of service.