ABSTRACT
Data communication occurs typically over three types of transmission systems: Dedicated, user-owned wire directly connected between the machines, LANs and Common carrier public networks. By far the largest volume of data handled and the largest amount of money spent is through common carrier public networks. Overvoltage protection is provided so that induced electricity from lightning or other phenomenon will not harm equipment at either the subscriber instrument or the central office. The network is built up by connecting instruments along with the subscriber loop to the transmissions links through switching systems. The two protocols of packet switching introduced in this book are X.25 and SNA. The authors have examined an abstract simplification from the most simple to the most complex. They covered local loops and transmission from cable to radio to satellite systems. Finally, they have traced switching from manual to mechanical to electronic to computerized circuit switching and from circuit switching to message switching to packet switching.
