Pick up your telephone and call a friend. As you punch the buttons, signals travel on the phone line to your local telephone centre. That centre sends the signals to the phone centre nearest your friend.
While you are calling your friend, thousands of other people are making calls, too! And some people are using modems. Modems are machines that send information from one computer to another over phone lines. Other people use fax machines or e-mail to send letters over phone lines. Today, people are sending out more messages than ever, and phone lines help us to communicate across the world!
Microwave links and optical fibres can handle many thousands to millions of phone calls at the same time. Microwave links send signals as a radio beam. At the receiving station, the microwave signals are decoded. Optical fibres are long strands of coated glass. Cables made of these strands use lasers to turn messages into pulses of light. The light pulses are then decoded at the other end of the optical fibre. These cables can carry millions of telephone conversations and faxes, as well as computer information. They can also be used to carry television programmes.
Picture Credit : Google
