1. INTRODUCTION

Without a QoS mechanism, an IP network provides the "best effort" service. In the best effort service, all packets are indistinguishable and are given the same forwarding treatment. A QoS mechanism in the IP network provides a means of distinguishing the packets and treating them differently. Two main QoS mechanisms available for the IP network are the Integrated Services (IntServ) and the Differentiated Services (DiffServ).

Figure 4-1 illustrates the best effort service, the IntServ and the DiffServ. In this illustration, the term "traffic flow" is used in a loose sense and represents the source of traffic. In the best effort service, all packets are lumped into a single mass regardless of the source of the traffic. In IntServ, individual flows are distinguished on an end-to-end basis. In DiffServ, individual flows are not identified end-to-end. Rather, they are aggregated into a smaller number of classes. Furthermore, these classes of traffic are given differential treatment on a per hop basis and there is no end-to-end treatment of these traffic classes.

Figure 4-1: Best effort, IntServ, and DiffServ.

This chapter discusses the generic functional requirements in providing QoS over the IP network. The two specific IP QoS mechanisms, IntServ and DiffServ, are then discussed in Chapter 5.

To provide QoS over the IP network, the network must perform the following two basic tasks:

• Task 1 - differentiate between traffic or service types so that users can treat one or more classes of traffic differently than other types

• Task 2 - treat...