Communications systems serve many functions. It is possible to divide into four categories on functions.
A point-to-point configuration provides a dedicated link between two devices. The entire capacity of the channel is reserved for transmission between those two devices. Most point-to-point line configuration use an actual length of wire or cable to connect the two ends.
A broadcast system send the same signal to everyone who receives it. In its usual form , transmission is one way, from the signal source to the individual. Local radio and television transmission are good examples of pure one-way broadcast systems.
A switched system makes temporary connections between terminals so they can exchange information. The telephone is a good example.
A network connects many terminals that can communicate with each other. For example Local Area Network is belongs to this category.