There are actually two layers in TCP/IP: the Internet Layer and the Transport Layer. In order to create an equivalence with the seven layers of the Open System Interconnection (OSI) protocol stack, many network teaching institutions have added a big block below the Internet Layer, which jacks up the two TCP/IP layers to the height of the corresponding OSI layers. As there is nothing above the Transport Layer to match the Presentation Layer and the Application Layer of OSI, you will now see a large Application Layer block drawn into the TCP/IP stack. Adding these two blocks for teaching purposes brings the total number of layers in the TCP/IP stack up to four.