This book describes lucidly asynchronous and synchronous data, multiplexers, radio waves propagation, VHF, microwaves, VSAT and satellite communication links and data transmission modes in such a manner that students of science, arts or commerce streams can understand these technical subjects easily. Data modem, multichannel data communication and pulse code modulation are dealt in detail, data networks and topology - both logical and physical - are described followed by a large number of understanding. Most of these topics are included in the curriculum of BCA, B.E Courses in computer science and electronics as well as in MCA, AMIE, IETE, GNIIT courses and also in diploma courses conducted by technical boards of education. It is hoped that this book will serve the dual purpose - a textbook for all these courses and an extremely useful reference source for experienced electronic engineers and computer professionals.