The telecommunication systems of companies have transmitters that take information and convert it into signals. The signal is transmitted over a transmission medium. A receiver then receives the information and converts it back into usable information. Signals are either analogue or digital.
In the case of the former, the signal is varied continuously with respect to the information while in the latter, the information is encoded as a set of discrete values.
Network is the most important concern of telecom companies. They form a part of this network which is a collection of transmitters, receivers that communicate with each other. Digital networks consists of one or more routers while analogue networks consist of one or more switches establishing connection between two or more users. Channels, on the other hand, is a division in a transmission medium that sends multiple sets of information. Modulation involves the shaping of a signal to convey information.
The telephone services provided by telecom companies works on a system where the caller is connected to the other person by switches at various telephone exchanges. A small microphone in the caller's handset transforms the caller's voice into an electrical signal. Companies provide fixed line phones which are analogue. Mobile phones are another form of service provided by the companies. They outnumber the fixed line in subscription in many places worldwide. Telephone communication has adopted systems based on optic fibers.
Radio and television are a part of the broadcast system where a central high-powered broadcast tower transmits a high frequency electromagnetic wave to numerous receivers. The Internet is another major service provided by the telecom companies. The computer networks communicate with each other using the Internet Protocol. The Local Area Networks are also prevalent even now while telegraph facilities are on the decline.
Telecom companies are an important part of our society. In 2006, the telecom industry's revenue was calculated at $1.2 trillion. The major telecom companies of the world are AT&T, Bell, Ace Communication, Armstrong Telecom Company, Avaya, etc.