What is communication media ? Discuss different types of communication media used in networks.

Communication media refer to the ways, means or channels of transmitting message from sender to the receiver.

Communication media can be grouped in two categories:

1. Guided media — These media include cables. There are three basic types of cables :
   1. Twisted-Pair Cables — These cables consist of two identical wires wrapped together in a double helix. These are also used for short and medium range telephone communication. The two types of twisted pair cables are Unshielded twisted pair cable (UTP) and Shielded twisted pair cable (STP).
   2. Coaxial Cables — This type of cable consists of a solid wire core surrounded by one or more foil or wire shields, each separated by some kind of plastic insulator. The inner core carries the signal, and the shield provides the ground. It is suitable for high speed communication. It is widely used for television signals. The two types of coaxial cables are thicknet and thinnet coaxial cable.
   3. Fiber-optic Cables — Optical fibres consist of thin strands of glass or glass like material which are so constructed that they carry light from a source at one end of the fiber to a detector at the other end. The fiber consists of core, cladding, protective coating. The bandwidth of the medium is very high. The two types of optical fibres are single mode and multimode fiber cables.
2. Unguided media — These media include waves through air, water or vacuum.
   Unguided communication media are as follows:
   
   1. Microwaves — The microwaves are similar to radio and television signals and are used for long distance communication. Microwave transmission consists of a transmitter, receiver and the atmosphere. The microwave transmission is line-of-sight transmission.
   2. Radiowaves — The transmission making use of radio frequencies is termed as radio-wave transmission. This transmission includes transmitter, receiver and antenna.
   3. Satellites — Satellite communication use the synchronous satellite to relay the radio signal transmitted from ground station. This transmission includes transponders.