This book attempts to provide a unified overview of the broad field of data and
computer communications. The organization of the book reflects an attempt to
break this massive subject into comprehensible parts and to build, piece by piece, a
survey of the state of the art. The book emphasizes basic principles and topics of
fundamental importance concerning the technology and architecture of this field, as
well as providing a detailed discussion of leading-edge topics.
The following basic themes serve to unify the discussion:
Principles: Although the scope of this book is broad, there are a number of
basic principles that appear repeatedly as themes and that unify this field.
Examples are multiplexing, flow control, and error control. The book high-
lights these principles and contrasts their application in specific areas of tech-
Design Approaches: The book examines alternative approaches to meeting
specific communication requirements. The discussion is bolstered with exam-
ples from existing implementations.
Standards: Standards have come to assume an increasingly important, indeed
dominant, role in this field. An understanding of the current status and future
direction of technology requires a comprehensive discussion of the role and
nature of the related standards.
Plan of the Text
The book is divided into four parts:
1 Data Communications: This part is concerned primarily with the exchange of
data between two directly-connected devices. Within thisrestricted scope, the
key aspects of transmission, interfacing, link control, and multiplexing are
11 Wide-Area Networks: This part examines the internal mechanisms and tech-
nologies that have been developed to support voice, data, and multimedia
communications over long-distance networks. The traditional technologies of
packet switching and circuit switching are examined, as well as the more
recent frame relay and ATM.
I11 Local Area Networks: This part explores the quite different technologie