As models go it’s pretty good, and no one has made a better one. Seriously. The layers are all useful concepts to know about and discuss, even if in some cases

As models go it’s pretty good, and no one has made a better one. Seriously. The layers are all useful concepts to know about and discuss, even if in some cases it is most practical to blur the lines or outright combine two of them into one protocol. You will at least know that you are doing so, and you will know to point out _why_ you are. But nobody has ever determined that it is _always_ best to combine two of the layers (which would really amount to proving that the two are in fact the same thing). But since nobody can prove that it is _never_ a good idea either, it remains a model and not a theorem with a proof. Edit: but I will also say that any test or certification which focuses too much on the OSI model is also suspect. I don’t know what test you’re about to take, but plenty of people will sell you certifications that in the end are meaningless.