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I need to map TCP/IP protocols to the OSI model for some university test revision I am doing.

I was wondering if it is generally acceptable to assume any OSI Level 7, 6 and 5 protocol will be transferred directly into TCP/IP's Layer 4 (Application Layer).

Obviously with TCP/IP to OSI mapping, you have to use more common sense, such as MMS from TCP/IP Application would go to Presenation Layer.

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    not really a network engineering question... since it is applied theory, stackoverflow is probably a better home for the question – This Jun 5 '13 at 16:28
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    I don't feel it is off topic, as the theory behind networking should not be strictly off topic. – YLearn Jun 5 '13 at 16:40
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    @YLearn, the about page mentions "real problems". This is hardly qualifies as a real problem from a network engineering perspective. However, we routinely answer questions like this on Stack Overflow – This Jun 5 '13 at 16:47
  • @MikePennington I know there are questions like this on SO, but I don't think SO is the place for this question, as is is strictly confined to the subject of networking, not programming in anyway. – jwbensley Jun 5 '13 at 21:09
  • @javano, officially computer science questions belong on Stack Overflow... this is best-described as a computer science question – This Jun 5 '13 at 21:45
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Yes. Both of the OSI and TCP/IP models are pretty old at this stage, and the TCP/IP model was created more specifically to "operate" with the IP protocol suite (the TCP/IP model slightly predates the OSI model). The OSI model was created by the ISO (International organization) and TCP/IP model was created by the U.S. and is maintained by the IETF. Even if TCP/IP didn't turn out to be the predominant protocol suite used on the Internet as we know it, with things like Moore's law and increasingly complex applications/protocols that can span multiple layers, the OSI model is becoming somewhat obsolete.

The reason why layers 7, 6 and 5 are all crammed into the Application layer in the TCP/IP model is that the folks that created the TCP/IP model believed that those responsibilities should be handled by the application itself, rather than within neatly laid out abstraction layers (thus helping to ease potential confusion that your question calls out).

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  • All I learned in school (early 1990s) was the OSI layer... I wonder if people are still being taught this? – This Jun 5 '13 at 16:57
  • It wouldn't surprise me. I think it's kind of a conundrum in the sense that the OSI model is a better teaching tool because it tries to fit things into distinct separate layers of responsibility, whereas (IMO) the TCP/IP model does a better job of reflecting reality, but it may be harder for folks that are just learning networking to conceptualize. I graduated in the early 2000's and the OSI model was also given much much more preferential treatment than the TCP/IP model. – John Jensen Jun 5 '13 at 17:02
  • @JohnJensen, actually, as I recall, the TCP/IP model actually predates the OSI model. While they can both trace their origins back into the 1970's, the TCP/IP four layer model goes back further to the DoD/DARPA model. – YLearn Jun 5 '13 at 20:37
  • Sure, but I never said or meant to imply that the TCP/IP model was "newer" than the OSI model, just that the OSI model is becoming obsolete, and has been for decades; even if you take Moore's law out of it - there's still TCP/IP itself. I think if things were different and IP never became as ubiquitous as it is today, the OSI model would be more relevant, but that's just not the way things turned out. :-) I still don't debate the usefulness of it as a teaching tool however. – John Jensen Jun 5 '13 at 22:51
  • Edited my original answer to be more clear and to make sure I'm not spreading misinformation re: either model's 'seniority'. :-) – John Jensen Jun 5 '13 at 23:02
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The OSI and TCP/IP are different models and everything doesn't always line up perfectly in practice. In going from OSI to TCP/IP, everything above TCP (OSI Layers 5-7) is considered the Application layer (TCP/IP Layer 4). From TCP/IP to OSI there can be a lot of disagreement over what falls into each of layers 5-7.

To add to the complication there are protocols which span multiple layers, for example, Ethernet is both layer 1 AND 2 in the OSI model.

Here is a nice visual.

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  • Of course Ethernet itself itself has a layered design. You have the frame formats (common across all ethernet variants and in some cases some of which are shared with other parts of 802), then you have medium access control (speed dependent but common across physical layers for the same speed), then the line coding (sometimes shared between different physical mediums, sometimes not) and finally the electrical or optical interface. – Peter Green Jul 28 '16 at 17:07

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