TABLE OF CONTENTS In recent years, the importance of Quality of Service (QoS) technologies for packet networks has increased rapidly. Today, QoS is undoubtedly one of the central pieces of the overall packet network technologies. How has QoS come to take such an important place in packet networks? This section reviews the recent history of telecommunications network evolution to put this fundamental question underpinning this book in perspective.
Referring to Figure 1.1, in the beginning of telecommunications, there were in general two separate networks, one for voice and one for data. Each network started with a simple goal of transporting a specific type of information. The telephone network, which was introduced with the invention of telephone by Alexander Graham Bell some hundred years ago, was designed to carry voice. The IP network, on the other hand, was designed to carry data.
In the early telephone network, the terminal device was a simple telephone set, which was nothing more than an analog transducer designed to produce an electrical current fluctuating with the speaker's acoustic pressure. For all practical purposes, this was all the function that the terminal device had to perform. The network itself, on the other hand, was more complex than the terminal, and was provided with "intelligence" necessary for providing various types of voice services.
A telephone connection is dedicated to a call during the entire period. Once the call is complete, the circuits are used to set up other calls. The circuits...
