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Identifying OSI

Checking through the Apprentice’s work this morning I found a list of the Seven Layers of the OSI Model. A good thing for him to know about, of course. A staple of any course in computer networking, and dead cert for an exam question.

I can even remember “Aged Pensioners Sing Twice Nightly Despite Pavarotti” myself. (Actually, I was quite surprised I could still remember this, over a quarter of a century since I was last asked to list the OSI layers in an exam.)

I started to wonder what exactly he was supposed to know about the OSI model, so I took at look. The requirement was to: “Identify the Seven Layers of the OSI Model”. This, I suppose, had been done well enough.

In the education world, we get very worked up about the verbs we use to describe learning. We might say that to “list” something is easy, to “describe” something is harder, to “understand” is deeper, and so on. We aim to work up to verbs like “theorise” or “extrapolate”. For the level we were at with this task, though, “identify” was just fine.

But, what is really the point of knowing about the OSI model. The idea (as I remember it) is that each layer in the model is aware of the layers above and below, but cares little for the rest of the stack. This is a concept that crops up over and over again in computing, of course. It exists in databases where I can write SQL queries without caring about where and how the data is stored. We all experience it daily when we visit a web page with no knowledge of where that page is stored, or what route the data making it up takes to get to our screens.

ThisĀ is what we want to the apprentice to understand. But that’s deeper; we’ll work on it.

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