Initially the OSI model was designed by the ISO to provide a framework on which to build a suite of open systems protocols. The vision was that this set of protocols would be used to develop an international network that would not be dependent on proprietary systems.

Ultimately, the speed at which the TCP/IP-based Internet was adopted, and the rate at which it expanded, caused the development and acceptance of the OSI protocol suite to lag behind. Although a few of the developed protocols using the OSI specifications are widely used today, the seven-layer OSI model has made major contributions to the development of other protocols and products for all types of new networks.

The OSI model provides an extensive list of functions and services that can occur at each layer. It also describes the interaction of each layer with the layers directly above and below it. Although the content of this course is structured around the OSI reference model, the focus of discussion is the protocols identified in the TCP/IP protocol model. Click each layer name to view the details.

Note: Whereas the TCP/IP model layers are referred to only by name, the seven OSI model layers are more often referred to by number rather than by name. For instance, the physical layer is referred to as Layer 1 of the OSI model.