Following are the major communication media used today.
1. Twisted-Wire Pair: Twisted wire pairs are commonly used in local telephone communication and for short distance digital data communication. These are usually made up of copper and the pair of wires is twisted together. Data transmission speed isnormally 9600 bits per second in a distance of 100 meter. They are affected by noise. They get weakened over long distances and therefore need to be boosted.
2. Coaxial Cables: Coaxial cable is a group of specially wrapped and insulated wires that are able to transfer data at higher rate. They consist of a central copper wire surrounded by an insulation over which copper mesh is placed. They are used for long distance telephone lines and local area network for their noise immunity and faster data transfer.
3. Microwave: Microwave system uses very high frequency radio signals to transmit data through space. The transmitter and receiver of a microwave system should be in line-of-sight because the radio signal cannot bend. With microwave very long distance transmission is not possible. In order to overcome the problem of line of sight and power amplification of weak signal, repeatersare used at intervals of 25 to 30 kilometers between the transmitting and receiving end. This is a non-physical or un-guided communication media.
4. Communication Satellite: The problem of line-sight and repeaters are overcome by using satellites, which are the most widely used data transmission media in modern days. A communication satellite is a microwave relay station placed in outer space. INSAT-IB is such a satellite that is accessible from anywhere in India. In satellite communication, microwave signal is transmitted from a transmitter on earth to the satellite in space. The satellite amplifies the weak signal and transmits it back to the receiver. The main advantage of satellite communication is that it is a single microwave relay station visible from any point of a very large area. In microwave the data transmission rate is 16 giga byte per second. They are mostly used to link big metropolitan cities.