The communications and networks technology had always fascinated me. I had graduated in Chemical Engineering from IIT and therefore, did not have too much of insight into the technical details of Telecommunications or Data Communications. May be, that is why there was this fascination. Many years back, I came across a book called "Great Ideas in Communication". It gave interesting and thrilling stories of how communications technology came into being from the historical days to the latest times of satellites and computers. It was extremely absorbing and my awe and respect for the communications and networks technology increased significantly.

When I joined Patni Computer Systems (PCS), I had around eight to ten years of applications software development experience of working with companies such as, IBM, Hindustan Lever, etc. in India, Europe and the U.S. I found all the details and intricacies of these applications such as finance, MRP II, CRP, retail and many others very interesting and the interfaces between them very challenging. I had a reasonable insight into all of these applications, having designed most of them, for which I had also been awarded at IBM and other companies many times. But PCS posed a new challenge. Mr. Narayana Murthy had left PCS and I was to run the Software Division after him. The expectations therefore, were very high. Mr. Narayana Murthy was, and still is, a great figure in the software industry, not only because of his commercial success but also because of his technical depth.

My initial months at PCS were very tough, though the people were very nice and cooperative. The reason was that majority of the business at PCS at that time was in the area of systems software and had to deal with Operating Systems, Compilers, Data Communications and so on. I was completely lost in the heavy jargon that we had to use every day. In fact, I had developed tremendous inferiority complex, as I really did not understand the technology very well.

However, I decided to plunge into these subjects with great determination. Luckily, a few friends also encouraged me. It was a strenuous and difficult path because I had to understand the entire subject from the very basics. There were excellent books on the subject, but very few started from the very beginning without assuming any knowledge on the part of the reader. Having read a lot on the subject, I finally thought that I should now explain the same subject in very simple terms to the readers so that they do not suffer the pains that I had to. My first book, Operating Systems was born out of these marathon efforts. I was far more encouraged when I got some excellent reviews for the book and when it went into its tenth re-print. After this, I turned my attention to Data Communications and Networks (DCN), a subject which had always enchanted me. Especially after the advent of the Internet, I was convinced that networking holds the key to the future of mankind. It took me a few years to come up with a style that would be simple, step-by-step but, still accurate and fairly deep. The current text is an outcome of the same.

This book is designed to serve as a textbook for the graduation and under/postgraduation levels such as BE, B.Tech, MCA, M. Sc., BCS, etc. The book assumes absolutely no previous knowledge on the subject or proficiency in Mathematics and goes on to explain the topic in simple step-by-step fashion. A large number of figures assist in the comprehension of the topic.

Chapter 1 covers the basics of data communications, and discusses various organizations, committees and bodies that help formulate the data communications standards. It then goes on to discuss the foundations of data communications.

Chapter 2 deals with the concepts of information encoding. How and why digital transmission is so vital, can be understood very clearly after reading this chapter.

Chapter 3 deals with the various analog and digital transmission techniques. Terms like modulation are explained here.

Chapter 4 deals with the modes of communication and the idea of multiplexing. Here, we see how a single communications channel can be used to combining signals from multiple sources.

Chapter 5 deals with the handling of transmission errors. Here we study how errors in data transmission can be detected and repaired.

Chapter 6 introduces the ideas of data compression and encryption. Data compression helps in terms of reducing the size of the data to be transmitted by using intelligent techniques. The concept of encryption is central to modern secure computer networks, and moreover, the Internet. This chapter deals with the ideas related to encryption.

Chapter 7 discusses the transmission media in detail. It covers both guided media such as twisted-pair, coaxial cable, optical fiber as well as unguided media such as radio and satellite.

Chapter 8 deals with various networking topologies, the concept of switching and then proceeds to discuss various routing algorithms.

Chapter 9 introduces the concept of protocols. Here, we understand the importance and significance of protocols in data communications. We also introduce and elaborate the OSI model in depth.

Chapter 10 examines the three main types of computer networks: Local Area Networks (LAN), Metropolitan Area Networks (MAN) and Wide Area Networks (WAN). We see examples of each type along with relevant discussions.

Chapter 11 covers the modern digital data and voice-integrated network, namely Integrated Services Digital Network (ISDN).

Chapter 12 discusses the relatively old but still quite popular X.25 protocol. We examine why it is losing its popularity these days.

Chapter 13 introduces the "modern version of X.25" viz. Frame Relay. We study the differences between X.25 and Frame Relay and discuss all the other relevant topics in relation to Frame Relay.

Chapter 14 covers the exciting new technology of Asynchronous Transfer Mode (ATM). We discuss how and why ATM is the future of data communications and networks.

Chapter 15 introduces the idea of internetworking. This chapter discusses the ‘what’ of internetworking followed by detailed history and architecture of the world’s most popular computer internet work—The Internet.

Chapter 16 discusses the various ways in which one can access the Internet. We will see how a dial-up connection works, discuss DSL, cable modem, leased lines etc.

Chapters 17 through 20 examine the TCP/IP protocol suite in great depth. These chapters cover all the major TCP/IP protocols with plenty of examples and diagrams. Chapter 17 discusses the protocols in the network/Internet layer, such as the Internet Protocol (IP), Address Resolution Protocol (ARP), Reverse Address Resolution Protocol (RARP) and Internet Control Message Protocol (ICMP).

Chapter 18 is dedicated to the transport layer of the TCP/IP suite of protocols. Here, we study the Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) in detail, and also see the differences between the two.

Chapter 19 deals with one portion of the protocols in the application layer of the TCP/IP suite. Here we study Domain Name System (DNS), Electronic mail (Email), File Transfer Protocol (FTP), and Trivial File Transfer Protocol (TFTP).

Chapter 20 concludes our discussion with the second portion of the protocols in the application layer of the TCP/IP suite. Here, we examine the World Wide Web (WWW), Hyper Text Transfer Protocol (HTTP) and remote login (TELNET).

This book would not have been possible without the assistance of many individuals, the most remarkable and noteworthy of them is Atul Kahate. He is one of the most methodical, intelligent and sincere person with a great ‘learning attitude’ that I have met. He helped me in formulating my thoughts and assisted me in a number of chapters. It is unthinkable to have finished this book without his help. I also want to thank my colleagues at Patni Computers – Satish Joshi and Vijay Khare who are not only some of the brightest IT professionals that I have seen, but who in fact, indirectly influenced me into studying these subjects very thoroughly (may be, they are not even aware of this!). I also want to thank Shobha Godbole who has designed the cover of this book. She is a great artist and without her innovative ideas, I do not think, the book would have been as attractive, as I hope it is. Needless to say, I have to mention all my family members, especially my parents, my brother and my sisters, Mr. Shriram Pujari who have taught me that the curiosity and inquisitiveness as well as quest for knowledge are far more valuable and important than accumulation of wealth in life. I owe a lot to them. My friends including Suhas and Ravi Malde, Sarika and Suresh Joshi, Smitha and Nandu Kolhatkar and Alka and Pradeep Kulkarni have always encouraged me in doing something new in life. I owe a lot to them too.

A S Godbole