Connection between OSI and IPS models

The OSI model was originally invented when the main computers where main frames. Making layer 5 more important however in modern applications the roles and responsibilities of the last 3 layers in the OSI get very mixed and end up being combined into one in other. Some applications might not implement some of them.

For example HTTP uses cookies for layer 5, extended ASCII for layer 6, and keywords for layer 7. Whereas FTP doesn’t have a way to implement layer 5, uses the same extended ASCII for layer 6 but different commands for layer 7.

This mix of these layers is normally dependent on the protocol - so normally rolled up into one thing.