Evolution of the OSI Reference Model

Posted on in Networking

The Open Systems Interconnection (OSI) Reference Model first came into being in 1978. The OSI group was intent on getting a model into the field quickly, so they elected to adopt a seven-layer model created by Charles Bachman of Honeywell. By this time, the lower four levels of the model had already been well established, but the upper layers needed to be fleshed out. As can be expected, there was a great deal of debate regarding what went into the session, presentation, and application layers (Day, 2008).

The biggest obstacle faced by the OSI group was the division between computer professionals and the operators of the Public Switched Telephone Network (PSTN). In an effort to fit the OSI model around their existing products, telephone operators blocked reasonable discourse at every turn. The OSI group was finally forced to concede the details of the session layer to European telephone operators. This resulted in a session layer that has nothing to do with the creation or maintenance of sessions (Day, 2008).

Eventually, the OSI group fleshed out each of the layers that make up the OSI Reference Model. They were constrained by conflicting interests such as the telephone operators and others with economic interest in the outcome of the model. Additionally, having committed to a system of layers early in the process, the group was unable to modify these layers when it became obvious that the accepted hierarchy did not fit the developed model. In the end, the OSI Reference Model remains a useful architecture. Had it focused more on future development than the inclusion of legacy systems, it might have been more successful (Day, 2008).


Day, J. (2008). Patterns in network architecture: A return to fundamentals. Boston: Pearson Education.

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