As history has shown, the world is, in itself, a rapidly developing system. Which requires all its subsystems to be able to meet its present demands immediately.
Computing, although still only relatively a child, has experienced mass changes over its short life. To keep up with societies recent ever changing demands the telecommunications industry has been forced to create the history of Open Systems.
ISO/IEC are national standards bodies and they along with a number of other groups took it upon themselves to take responsibility for the formation of a standarised system: OSI: Open System Interconnection. Standards indicate how the functionality of the layer can be achieved by the cooperation of two implementions of a layer standard, one at either end of the communicating systems.
Complex testing and difficult modification is closely associated with implementing software for communication subsystems. To overcome these problems OSI/IEC adopted a Layered Approach .