Data communication consists of five basic components.
The message is the information or data to be communicated. i can be text, numbers, pictures, sound or video or combination of these.
The sender is the device that sends the message. It can be a computer, work station, camera etc..
The receiver is the device that receives the message.It can be a computer, work station, television etc..
The transmission medium is the path by which message trevels from sender to receiver. It can be a wire, coaxial cale, fibre optics, laser or radio waves etc..
A protocol is a set of rules that governs the data communication. It represents the agreement of communicating devices. Without a protocol devices can not communicate to each other.