Mapping models

There’s actually two (at least) conceptual models in networking: the OSI model and the TCP/IP model. I had assumed they were the same – vaguely – but they are related in the best way that layered ideas could be: TCP/IP can be mapped onto OSI if you consider OSI as a generic model of a “communications stack.”

If you hear the phrase “Ethernet is layer 1 and 2 of the OSI model” or “TCP is the layer 4 protocol of the OSI model,” that means the TCP/IP concepts are fitted in the OSI stack from Physical (layer 1), Data Link (layer 2) to Transport (layer 4), and beyond.

Regarding network tools, it seems there’s a lot of emphasis on packets: filtering packets, inspecting packets, crafting packets. Less so, seemingly, on the wrapped portions of the data, into frames and segments, and the transmission of bits.

Perhaps because the “transport” layer in both models are the boundary between the application space and the data flow, where the best vectors can be found.

Layers and literals

There is actually a difference between phone connections and network connections. I imagined both the same, solid bold lines bent through rigid corners, each endpoint a communications device. This is true of phones and “circuit-switched” networks, but not so for packet-oriented networks like the Internet. The logical layer of “a connection” does not match the implementation.

Conceptually, packets may not travel the same route. They travel across the ebb and flow of pipes, big ones and little ones, whose marketed bandwidth is a shadow of the actual performance, the throughput. Such “layer thoughts” should not surprise me; initial assumptions ought to consider a certain implicit inaccuracy.

“It’s all software; hardware is irrelevant,” a colleague said. He looked around at his office of spare parts and sitting appliances. He wanted to learn about cylinders, databases. Software had eaten the world, and he was catching up.