Principles of Communications Networks and Systems

Book Preface

This book addresses the fundamentals of communications systems and networks, providing models and analytical methods for evaluating their performance. It is divided into ten chapters, which are the result of a joint effort by the authors and contributors. The authors and the contributors have a long history of collaboration, both in research and in teaching, which makes this book very consistent in both approach and in the notation used.

The uniqueness of this textbook lies in the fact that it addresses topics ranging from the physical layer (digital transmission and modulation) to the networking layers (MAC, routing, and transport). Moreover, quality of service concepts belonging to the different layers of the protocol stack are covered, and the relationships between the metrics at different layers are discussed. This should help the student in the analysis and design of modern communications systems, which are better understood at a system level.

A suitable selection of chapters from this book provides the necessary teaching material for a one-semester undergraduate course on the basics of telecommunications, but some advanced material can be also used in graduate classes as complementary reading. The book is also a useful comprehensive reference for telecommunications professionals. Each chapter provides a number of problems to test the reader’s understanding of the material. The numerical solutions for these exercises are provided in the companion website, www.wiley.com/go/ benvenuto2.

The content of each chapter is briefly summarized below. Chapter 1 Overview of modern communications services, along with the presentation of the OSI/ISO model.

Chapter 2 Analyzes both deterministic signals and random processes. The chapter revises the basics of signal theory and introduces both continuous and discrete time signals, and their Fourier transform with its properties. The concepts of energy, power and bandwidth are also reviewed, together with the vector representation of signals by linear space methodologies. Lastly, this chapter introduces the basics of random variables and random processes, their common statistical description, and how statistical parameters are modified by linear systems.

Chapter 3 Describes how information produced by a source, either analog or digital, can be effectively encoded into a digital message for efficient transmission.We will first introduce the reference scheme for analog-to-digital conversion, and focus on quantization, the operation of approximating an analog value with a finite digit representation. We will also present the fundamentals of information theory with the notion of information carried by a digital message. Lastly we introduce the principles of source coding, state the fundamental performance bounds and discuss some coding techniques.

Chapter 4 Models a transmission medium. Firstly, a description of the two-port network is given. A model of noise sources is then provided and its description in terms of parameters such as the noise temperature and the noise figure is presented.Acharacterization, especially in terms of power attenuation, of transmission lines, power lines, optical fibers, radio propagation and underwater propagation concludes this chapter.

Chapter 5 Deals with digital modulations. The general theory is first presented, relying on concepts of linear spaces and hypothesis testing. Performance is measured by the bit error probability, which again can be expressed in terms of system parameters. Then, the most important modulations are presented as examples of the general concept. These include pulse amplitude modulation, phase shift keying, quadrature amplitude modulation, frequency shift keying and others. A comparison between the different modulation schemes is carefully drawn. Then, more advanced modulation techniques are briefly presented, namely orthogonal frequency division multiplexing and spread spectrum. Finally, the performance of the digital approach is compared against analog transmission, explaining why digital transmission is so widely used.

Chapter 6 Investigates how an information message can be robustly encoded into the signal for reliable transmission over a noisy channel. We describe the principles of channel coding techniques, where robustness is obtained at the price of reduced information rate and complexity of the decoding process. Then, based upon the fundamentals of information theory introduced in Chapter 3, we aim to establish upper bounds on the amount of information that can be effectively carried through a noisy channel, by introducing the concept of channel capacity. We conclude by describing briefly how recently devised coding schemes allow such upper bounds to be approached closely while maintaining moderate complexity.

Chapter 7 Introduces some basic statistical methods that are widely used in the performance analysis of telecommunication networks. The topics covered are the elementary theory of discrete-time and continuous-time Markov chains and birth-death processes. This theory will be applied in Chapters 8 and 9, whereweanalyze simple queueing systems, and the performance of channel access and retransmission protocols.

Chapter 8 Presents some basic principles of queueing theory. It starts with the definition of a queueing system in terms of arrival, departure, service processes, queueing processes and service discipline. We then define some basic performance metrics for queueing systems, which are classified as occupancy measures (number of customers in the different parts of the system), time measures (system and queueing times) and traffic measures (average rate at which customer arrive and leave the system). We discuss the concept of system stability, both for blocking and nonblocking queueing systems and we illustrate Little’s law, a simple but fundamental result of queueing theory. The chapter concludes with a performance analysis of fundamental queueing models, featuring Markovian as well as non-Markovian statistics for the service process. Examples of the application of the developed theory to practical problems, including some unrelated to telecommunications, are provided throughout the chapter.

Chapter 9 Presents and analyzes link-layer algorithms, especially focusing on aspects related to channel access and retransmission of lost or corrupted data packets over point-to-point links – a technique often referred to as Automatic Retransmission reQuest (ARQ). Channel access protocols are subdivided into the following classes: deterministic access, demand-based access, random access and carrier sense multiple access. Mathematical models are given for each class of protocols, thus obtaining the related performance in terms of throughput and delay. The different channel access schemes are then compared as a function of the traffic load of the system. Next, the chapter presents three standard ARQ schemes, namely, stop and wait, go back N and selective repeat ARQ, which are characterized analytically in terms of their throughput performance. The chapter ends with the presentation of some relevant LAN standards: Ethernet, IEEE 802.11 and Bluetooth, with emphasis on their link-layer techniques.

Chapter 10 Describes all the layers above the data link layer dealing with the interconnection of distinct devices so as to form a communication network. The chapter begins by reviewing a useful mathematical tool for network analysis, namely graph theory. Routing methodologies, i.e., how to find efficient paths in the network, are identified and discussed within this framework. Subsequently, we review how the network layer is implemented in the Internet detailing the Internet Protocol (IP), as well as related issues, including Address Resolution Protocol (ARP) and Network Address Translation (NAT). The chapter describes the implementation of Transport Control Protocol (TCP) and the User Datagram Protocol (UDP)) and application (Domain Name Server (DNS)) layers for the Internet. Some examples of application protocols, that is, HyperText Transport Protocol (HTTP) and Simple Mail Transfer Protocol (SMTP) are given.