Communication is to transfer information from one place to another. Communication from a source to destination requires a proper methodology and technique. It requires a medium, source, message formation, storage and input for transmission etc. A reverse procedure at destination is repeated to get the exact message. This, in turn, requires a complete system for communication. Most popular media types used for communication between two computer systems, are twisted pair of wires, coaxial cable, fiber, optic cable, microwave and satellite. Communication between two systems can be established using the facility of media provided by telecommunication network (Telephone Lines) through modems, fax machines etc.
Modem is a modulating demodulating device. It encodes the data while sending and decodes it at the receiving end. Modem to modem communication is through telephone lines. Modem can be directly connected to a computer through a serial port.