What are communication channels ? Discuss various communication channels available for networks.

A communication channel is a means of communication between two devices or workstations i.e., it refers to the medium used to carry information or data from one point to another.

Communication channels 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 insulated copper wires twisted around each other. These are also used for short and medium range telephone communication.
   2. Coaxial Cables — A coaxial cable consists of one or more small cables in protective covering. These are more expensive than twisted pair cables but perform better.
   3. Fiber-optic Cables — These cables are made of plastic or glass and are about as thick as human hair. These cables are highly durable and offer excellent performance but are expensive.
2. Unguided media — These 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.
   2. Radiowaves — The transmission making use of radio frequencies is termed as radio-wave transmission.
   3. Satellites — Satellite communication use the synchronous satellite to relay the radio signal transmitted from ground station.