xiv Preface background in elementary probability and some background in either electrical engineering or computer science,but aside from this,the material is self-con- tained. Throughout the book,major concepts and principles are first explained in a simple non-mathematical way.This is followed by careful descriptions of mod- elling issues and then by mathematical analysis.Finally,the insights to be gained from the analysis are explained and examples are given to clarify the more subtle issues.Figures are liberally used throughout to illustrate the ideas.For lower- level courses,the analysis can be glossed over;this allows the beginning and intermediate-level to grasp the basic ideas,while enabling the more advanced student to acquire deeper understanding and the ability to do research in the field. Chapter 1 provides a broad introduction to the subject and also develops the layering concept.This layering allows the various issues of data networks to be developed in a largely independent fashion,thus making it possible to read the subsequent chapters in any desired depth (including omission)without seri- ously hindering the ability to understand other chapters. Chapter 2 treats the two lowest layers of the above layering.The lowest,or physical,layer is concerned with transmitting a sequence of bits over a physical communication medium.We provide a brief introduction to the subject which will be helpful but not necessary in understanding the rest of the text.The next layer,data link control,deals with transmitting packets reliably over a communi- cation link.Section 2.4,treating retransmission strategies,should probably be covered in any course,since it brings out the subtleties,in the simplest context,of understanding distributed algorithms,or protocols. Chapter 3 develops the queueing theory used for performance analysis of multiaccess schemes (Chapter 4)and,to a lesser extent,routing algorithms (Chapter 5).Less analytical courses will probably omit most of this chapter, simply adopting the results on faith.Little's theorem and the Poisson process should be covered however,since they are simple and greatly enhance under- standing of the subsequent chapters.This chapter is rich in results,often de- veloped in a far simpler way than found in the queueing literature.This simplicity is achieved by considering only steady-state behavior and by some- times sacrificing rigor for clarity and insight.Mathematically sophisticated read- ers will be able to supply the extra details for rigor by themselves,while for most readers the extra details would obscure the line of argument. Chapter 4 develops the topic of multiaccess communication,including local area networks,satellite networks,and radio networks.Less theoretical courses will probably skip the last half of section 4.2,all of section 4.3,and most of section 4.4,getting quickly to local area networks and satellite networks in sec- tion 4.5.Conceptually,one gains a great deal of insight into the nature of distributed algorithms in this chapter. Chapter 5 develops the subject of routing.The material is graduated in order of increasing difficulty and depth,so readers can go as far as they arePreface background in elementary probability and some background in either electrical engineering or computer science, but aside from this, the material is self-con￾tained. Throughout the book, major concepts and principles are first explained in a simple non-mathematical way. This is followed by careful descriptions of mod￾elling issues and then by mathematical analysis. Finally, the insights to be gained from the analysis are explained and examples are given to clarify the more subtle issues. Figures are liberally used throughout to illustrate the ideas. For lower￾level courses, the analysis can be glossed over; this allows the beginning and intermediate-level to grasp the basic ideas, while enabling the more advanced student to acquire deeper understanding and the ability to do research in the field. Chapter 1 provides a broad introduction to the subject and also develops the layering concept. This layering allows the various issues of data networks to be developed in a largely independent fashion, thus making it possible to read the subsequent chapters in any desired depth (including omission) without seri￾ously hindering the ability to understand other chapters. Chapter 2 treats the two lowest layers of the above layering. The lowest, or physical, layer is concerned with transmitting a sequence of bits over a physical communication medium. We provide a brief introduction to the subject which will be helpful but not necessary in understanding the rest of the text. The next layer, data link control, deals with transmitting packets reliably over a communi￾cation link. Section 2.4, treating retransmission strategies, should probably be covered in any course, since it brings out the subtleties, in the simplest context, of understanding distributed algorithms, or protocols. Chapter 3 develops the queueing theory used for performance analysis of multiaccess schemes (Chapter 4) and, to a lesser extent, routing algorithms (Chapter 5). Less analytical courses will probably omit most of this chapter, simply adopting the results on faith. Little's theorem and the Poisson process should be covered however, since they are simple and greatly enhance under￾standing of the subsequent chapters. This chapter is rich in results, often de￾veloped in a far simpler way than found in the queueing literature. This simplicity is achieved by considering only steady-state behavior and by some￾times sacrificing rigor for clarity and insight. Mathematically sophisticated read￾ers will be able to supply the extra details for rigor by themselves, while for most readers the extra details would obscure the line of argument. Chapter 4 develops the topic of multiaccess communication, including local area networks, satellite networks, and radio networks. Less theoretical courses will probably skip the last half of section 4.2, all of section 4.3, and most of section 4.4, getting quickly to local area networks and satellite networks in sec￾tion 4.5. Conceptually, one gains a great deal of insight into the nature of distributed algorithms in this chapter. Chapter 5 develops the subject of routing. The material is graduated in order of increasing difficulty and depth, so readers can go as far as they are I