Have you ever wondered how thousands of people make phone calls and communicate at the same time, yet there are only 4 wires on each telephone pole, that accommodate all these calls. We all know that the is one wire to our house and one to the house of the person we want to call, but how is it possible that our lines and the lines of every other person living in our neighbourhood, all send information through only one common line, and furthermore, how is everyones information received simultaneously at the other end?The answer lies in a simple concept called time division multiplexing. Although modern telecommunication networks use much faster and more efficient methods, time division multiplexing or TDM for short was an important communication technique in older days, and can still be used effectively for small networks.