I’m not a computer science student. But I want to learn it and grasp these two models in very simple language and terminology.
In: 7
The OSI model is a fiction that gets taught to students, which then everyone proceeds to mostly forget because it’s not quite accurate to the real world
The underlying idea is that you structure stuff in layers, and the upper layers don’t really care what’s going on below.
* Layer 1 is the physical layer. That determines how data is actually physically communicated. And this can be electrical pulses, or pulses of light (fiber), or electromagnetic radiation (wifi), or smoke signals. Nothing above really needs to care.
* Layer 2 is node to node communication — if you hook up a machine to another directly with a cable. Ethernet goes here.
* Layer 3 is networking — how stuff gets along a chain from A to B to C to D. The IP protocol goes here.
* Layer 4 is Transport — where you have the concept of a transferring arbitrary amounts of data from A to B. TCP goes here.
* Layer 5 is session — where you have the concept of a constant connection. TCP is also here.
* Layer 6 is presentation — concerned with formatting, compressing and encrypting data. For instance SSL.
* Layer 7 is application — which is whatever you run on top of all of this, like HTTP.
* Layer 8 is the user — not an actual layer, but something you might see people jokingly refer to.
In practice the layers that get talked about is 1, 2, 3 and 7:
* It’s a bad cable (layer 1)
* There’s two computers with the same MAC, or they’re not plugged into the same switch (layer 2)
* IP address is misconfigured (layer 3)
* Something is wrong with the application itself (layer 7)
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