Episode 08

The “Seven-Layer” Vocabulary of Modern Internetworking

Segment 4 of 5

In the late 1970’s, a group of influential vendors cooperating with standards bodies and with the involvement of governments throughout the world, formed an organization or joined forces with the International Standards Organization (ISO), and created a vocabulary, and a plan, and an architecture design for a new kind of networking. The design was called the Open Systems Interconnect (OSI), and the design divided the most common functions of networking into seven modular interoperable interchangeable layers. The open systems interconnect paper, published by the International Standards Organization back in 1977, provided the first really useful vocabulary to describe the logic of networks in a way that could be interpreted by many different vendors to allow interoperability. The paper became well-known as the “OSI Seven-Layer Architecture,” or the “OSI Seven Layer Reference Model for Network Design.”

As it turns out, this seven-layer design was highly regarded. It was received with enthusiasm by many different vendors and governments and customers, and it looked for a time as though all networks would eventually follow this seven-layer model. Unfortunately however, the ISO was burdened by a lot of bureaucracy. Although the OSI design was good, the actual implementation became increasingly complex and cumbersome and unwieldy, and by and large, the effort was entirely abandoned about 1996.

During that period of debate and transition, the Internet was growing and thriving, and the protocols used by the Internet turned out along similar lines to those used by the OSI, but the Internet protocols are simpler and easier to implement, and therefore became much more popular. Various bits of the OSI architecture survive today among the pieces of networks that do communicate, but by and large, the most important contribution of the OSI to networking is the vocabulary of networking and internetworking. Most network designers today still use the seven-layer vocabulary published by the OSI as they describe the components of today’s networking.

Because the OSI architecture divided the most common networking functions into seven hierarchical levels, it is commonplace today for network designers to describe their particular component as a layer-one component, or a layer-two component, or a layer-three component; all the way up to a layer-seven component, at increasing levels of intelligence. And the operations of our local area network in the Internet can be described pretty well in terms of the seven layers of the OSI model. You will be interacting with components in your small office network, or your home network that can be described very effectively with vocabulary of the OSI seven layer model.


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