The Open Systems Interconnection reference model aka OSI layers published by International Organization for Standardizations as a framework on which to build a suitable systems of open systems protocols. A primary model used when discussing network designers, functionality, protocols and many more. Basically network designers must relate their design to OSI model so it can be solution to solve incompatible connection between network and its interface.

OSI layers contain seven layers which more often referred to by number than by name, for example switch layer 3, network engineer should know that the switch operate at layer 3 or network layer. Here the layers:
• Layer 1: OSI Physical Layer
• Layer 2: OSI Data link Layer
• Layer 3: OSI Network Layer
• Layer 4: OSI Transport Layer
• Layer 5: OSI Session Layer
• Layer 6: OSI Presentation Layer
• Layer 7: OSI Application Layer

OSI Layers

As a reference model, the OSI layers provide an extensive list of functions and services that can occur at each layer. It also describes the interrelation of each layer with the layers directly above and below it. The OSI model has made important contribution to the development of other protocol, products and services for all types of new networks.