OSPF Network Design Solutions, Second Edition

Understanding the Seven Layers of the OSI Reference Model

The seven layers of the OSI reference model can be divided into two categories: upper layers and lower layers. The upper layers are typically concerned only with applications, and the lower layers primarily handle data transportation. The sections that follow examine the three upper layers, the four lower layers, and the functions of each.

Upper Layers

The upper layers of the OSI reference model—5, 6, and 7—are concerned with application issues. They are generally implemented only in software programs. The application layer is the highest layer and is closest to the end user. Both users and application layer processes interact with software programs that contain a communications component ...