What exactly is the Open Systems Interconnection?

In order to talk about communication protocols, we need to understand how each protocol fits into the larger picture of network connectivity, and to do that we need a common model for thinking about each step in the process. To that end, we have the OSI model for computer and telecommunication networks. This model seeks to organize the different steps of standardized communication to or from a given device into a tiered model of abstraction layers. Much like the logical topologies of a network, which we discussed in Chapter 1, Networks in a Nutshell, the OSI model exists on a purely conceptual and abstract level.

As the name suggests, it was defined in such a way as to be useful as a reference while remaining entirely agnostic as to how any of the tiers defined in the model are ultimately implemented at the physical level. In fact, many implementations of communications protocols or standards do not cleanly map to the OSI network model. However, the model is broadly considered the gold standard, and has been since it was formalized in 1984. So, let's take a look at how that came to be.