OSI model

This model is based on a proposal developed by the International Standards Organization (ISO) as a first step toward international standardization of the protocols used in the various layers (Day and Zimmermann, 1983). It was revised in 1995 (Day, 1995). The model is called the ISO OSI (Open Systems Interconnection) Reference Model because it deals with connecting open systems—that is, systems that are open for communication with other systems. We will just call it the OSI model for short.

The model defines six layers of software and one physical layer of hardware, as shown Figure 12-1:

  • I have a metaphor to describe the seven layers of functions and relations
    7 Application Layer: the boss
    6 presentation layer: the equivalent of company presentations boss, the assistant for the boss letter
    5 Session Layer: the equivalent of closing the company send a letter, write letters and envelopes, the secretary of demolition
    4 transport layer: the equivalent of running the post office messenger company staff
    3 Network Layer: the equivalent of post office workers in the sorting
    2 Data link layer: the equivalent of post office workers in the loading unboxing
    A physical layer: the equivalent of post office in the porters



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