Finally, after much ado—hopefully not too much!—it is time to take a look at the actual individual layers of the OSI Reference Model. As discussed in the section on OSI model concepts, each layer has certain characteristics that define it, and also various protocols normally associated with it. Understanding the nuances of each layer will help you understand all the technologies that use them.

In this section, I describe each of the OSI Reference Model layers individually. For each one I provide its name and layer number, describe its general function in the OSI layer stack, and outline the specific types of activities for which each is normally responsible. I also provide some examples of the technologies and protocols that reside at each layer. Keep in mind, however, that the descriptions in this section are generic. To really comprehend the various layers and how they are uses, there is no substitute for reading the details of the individual protocols that function at each layer, covered elsewhere in this Guide.