The IP suite is not nearly as neatly layered as OSI was and the OSI model doesn't neatly fit the IP suite since it wasn't actually designed for IP at all. In the IP suite layers 5 and 6 basically don't exist in the OSI sense, TCP handles things that are part of both layers 4 and 5 in the model despite being a single protocol, etc. The OSI model is often considered obselete as it just doesn't actually fit the IP world all that well but it's been around so long and does have uses in certain situations that it tends to stick around.