so i am going through cisco ccent/ccna. working through the text on my own just for general useful knowledge. so in the early part of the book it goes into describing the different layers of the TCP/IP suite, the protocols associated with each layer, how those layers interact with each other, and at the end compares the OSI network model. understanding the similarities and differences in the models, the application layer in TCP/IP corresponds to layers 7/6/5 in the OSI model...

so my question is this; the TCP/IP model itself is a representation of the different protocols used in the different abstraction levels of networking. protocols of the application layer are things like web browsers, protocols of the transport layer are TCP/UDP, protocols of the network layers are IP and others, and on the link layer are protocols like ethernet and others...

so what was given up with OSI when that was abandoned? did the different layers of the OSI models use different protocols, did the session layer of OSI not use HTTP, but something like HTTP? did the transport layer not use TCP but something like TCP? not IP but something like IP?

or was the difference between the models different than just different suits of protocols (obviously OSI used the application/presentation/and session layer where TCP/IP combined all of those functions into the application layer with the web browser and the like...)


The models are just models. The real world doesn't exactly match any of the models. There was no abandonment of OSI, or any other model. The models were created to try to explain how things would ideally work, but reality has a way of rearing its ugly head.

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  • so computers that implemented the OSI protocol still used web browsers/HTTP/TCP/IP/and ethernet protocols to bring networks to life? the only difference your saying between the models is the way we abstract the different functions of different parts of the network? – user74091 Mar 6 '16 at 20:37
  • Nobody actually implemented the OSI model. The OSI model was created to explain how things should work. Actually, modern networking fits surprisingly well with OSI layers 1 to 4, but OSes and application programmers really aren't all that interested in implementing layers 5 to 7 as defined by OSI. – Ron Maupin Mar 6 '16 at 20:42
  • i see, so the software protocols used to implement networks have always been the same. these names like TCP/IP and OSI are literally just that, representations of the different aspects of networking so people can conceptualize whats going on. – user74091 Mar 6 '16 at 20:47
  • well, yes and no, its better to say that some technologies have more direct degrees of conformance than others. The TCP and IP specs, for instance, are pretty closely followed by implementers. The OSI presented a spec OS stack, but no OS vendor choose to implement layers 5 and 6, because they force the app developer to rely on the OS for session and encoding services, which presents issues for cross-platform authoring, and requires the applications to strictly conform to those specs. Since the vendors never adopted, the OSI model remains partially theoretical and layer 7 does everything. – Frank Thomas Mar 6 '16 at 20:55

You already answered it yourself: TCP/IP conflicts with the OSI model by mixing OSI layers. The reasons for this are found in better performance.

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