When forming networks consisting of a set of computers and other devices we take care of converting it from the branching form of the transmitted computer to the serial form To be sent via telephone lines to the receiving computer And then we need to convert these data To the branching form at the receiving tip .We also take care of converting data from digital to analog so that we can send it over telephone lines, which is what modems do .The data transfer organization should be responsible for the detection and analysis of errors and the audit of data Networks are also concerned with the need to direct the data to the desired destination, meaning that there must be nominated (keys) that can elect the data that must be passed to this or that computer To prevent inertness during the transfer process, the analog signal must be amplified because it is important to know the frequency of this signal and not the shape of it . So a set of functions must be achieved in order to transfer data within networks .