To re-cap, in TCP/IP we only have five layers, above the Network layer we have a Transport layer and above the Transport layer we have an Application layer.

So in fact we are missing the Session and Presentation layers, completely from the IP model, yet that is not critical as IP works none the less.

You will hear a lot about the OSI model and networking, but the de facto standard is the IP model. So we will have the OSI model in the back of our minds but we are going to concentrate on the TCP/IP model.