An alternate explanation of the OSI model

This is an excellent piece on the purpose and shortcomings of the OSI model by Robert Graham of Errata Security.

The “OSI Model” that everyone learns isn’t actually correct. In the 1970s, each computer company had their own networking standards that couldn’t talk to each other. So, the international standards organization created a group to create networking standards, the OSI group. Half a decade later, the first thing they could agree on was a blueprint for how they were going to design standards. This “OSI Model” is not a model for how existing networks were designed (such as the Internet), but how the OSI group WANTED to design networks…

For example, I like to describe networking with the “as-far-as” model. Each layer is responsible for only getting the data part of the way to the destination…

Another way of describing the layers would be the “unit” model. Layer 1 sends bits. Layer 2 sends frames. Layer 3 sends packets. Layer 4 sends streams…

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