The International Standards Organisation came up with a series of definitions for networking, including a 7 layer model of networking with the idea that different vendors could implement their own protocols at each layer and they could all work together. Of course this was promptly ignored by everyone and they used TCP/IP which doesn't follow the 7 layer model, but people still talk about it today as if it was relevant.

|^Layer|^ISO OSI Model|||^TCP/IP Model |7|Application|vvPOP3|vIMAP|vvDNS |6|Presentation |5|Session|SSL |4|Transport ||v TCP|UDP |v3|vNetwork|IP ||| IP |2|Data Link Layer|||802.3? |1|Physical||802.3?|802.11