The purpose of a network is to transmit information from one computer to another. To do this, you first have to decide how to encode the data to be sent, in other words its computer representation. This will differ according to the type of data, which could be:
Data representation can be divided into two categories:
In order for data transmission to occur, there must be a transmission line, also called transmission channel or channel, between the two machines.
These transmission channels are made up of several segments that allow the data to circulate in the form of electromagnetic, electrical, light or even acoustic waves. So, in fact, it is a vibratory phenomenon that is propagated over the physical medium.
In order for data to be exchanged, an encoding must be chosen for the transmission signals. This depends basically on the physical medium used to transfer the data, the guaranteed data integrity and transmission speed.
Data transmission is called "simple" if there are only two machines communicating, or if only a single piece of data is sent. Otherwise, it is necessary to install several transmission lines or to share the line among several different communication actors. This sharing is called multiplexing.
A protocol is a common language used by all actors in the communication to exchange data. However, its role does not stop there. A protocol also allows: