this post was submitted on 01 Jan 2026
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What do you mean "Theoretical" and "Never been used"? Are you writing this by sending off radio waves purely with your mind? Am I the only one using a modem and computer? (/j, but it seems to me that you're asking "why a plane needs engines and wings, when it already has a payload")
TCP (and UDP) just describe how to assemble the data into packages which can be somewhat reliably reassembled on the other end.
While it does have an address stamped on top (IP), it doesn't know how to get anywhere by itself. That's where the bottom 3 OSI layers come in (the physical wires - or wireless spectra/wavelengths - the data is transmitted through, the specifications of how the embedded devices talk to each other over these wires, and how to discover other embedded or other devices on a network). I can very much assure you that the wires do exist and are indeed in use.
Contrary, the upper layers are more about keeping communication going once a connection has been established.
You're confusing TCP (the specific protocol) with the TCP/IP model, which is an entirely different model to describe the network stack to the OSI model, and which can only loosely be mapped onto it.
Apologies, that's my fault, I thought you wrote "TCP model(/protocol)" and not "TCP/IP model", which are indeed two very different things.
I feel that the OSI model focuses more on the specific layers with their relations and physical/digital setup, while the TCP/IP model has more of a abstract and "high-level"-focus. I think both have their ups and downs, though I'm still confused what about OSI is "theoretical and has never been used".
No, you read it right. I just assumed my meaning would be clearer than it apparently was. To me, the word "TCP model" doesn't strictly mean anything. There's the TCP protocol, and the TCP/IP model. I assumed my usage of the word "model" would make it clear that I meant the latter, but I guess I can see how people would interpret it as the former.
A real-world implementation of OSI would involve separate protocols for each layer. There have been numerous different ways of describing TCP/IP in terms of OSI layers, but roughly speaking, the broadest possible interpretation is that TCP/IP's "application layer" covers OSI layers 5, 6, and 7, with TCP covering layer 4, and IP layer 3. But some analyses also suggest TCP/UDP ports are a layer 5 concern. Ultimately, the TCP/IP networking model is a separate way of looking at things to the OSI model, and it would be silly to suggest that it's the same.
Just saw this comment.
Yes, you are completely right. That's likely also the reason for your confusion regarding OSI, since you appear to compare it to TCP/IP in a rather literal manner.
Obviously TCP/IP is better at describing TCP/IP than OSI, though while OSI also can be used to describe TCP/IP in a sub-optimal manner, TCP/IP cannot be used to describe OSI.