The functions were divided into seven sections and each of these functions was called a layer – and these layers are, of course, fake - For easy memorization of their order, the first words of the famous saying can be used: *(Please Do not Trust sales people Always)* The first three layers (bottom) depends on the hardware , while the top three layers on software، the Middle is used as a link between application-related services and network services. To build a network, key parts such as peripherals (workstation), network Devices and transmission Media must be provided. The OSI Model consists of seven layers and is shown in the picture.