Telephone Systems:

A complete telephone system block diagram is shown in Fig.11.4. On the left, three subscribers are shown. The

top one is an office with three phones and a terminal/computer (T/C). The digital signal of the T/C is converted to analog by the modem. The office system is internally tied together via its private branch exchange (PBX). The PBX also connects it to the outside world, as shown. The next subscriber

DIGITAL DATA TRANSMISSION:

There is a gradual transition taking place in types of communications traffic. Formerly, it

was mostly analog in nature, but we now are experiencing a more digital than analog

situation. This transition has been caused by the increasing use of