OSI Reference Model This model is based on a proposal by ISO revised in 1995. The model is called the ISO-OSI(open System Interconnection) as it deals with connecting open systems – that is systems that are open for communication with others. The principles that were applied to arrive at the seven layers can be briefly summarised as: A layers should be created where a different abstraction is needed Each layer should perform a well-defined function The function of each layer should be chosen with an eye toward defining internationally standardised protocols The layer boundaries should be chosen to minimize information flows across the interfaces The number of layers should be large enough that distinct function need not be thrown together in the