Now we are getting somewhere. In the OSI standard, they list the principles used to determine the seven layers in the Reference Mode. (ISO/IEC 7498-1:1994, Section 6.2). Among those principles are: ...

The application layer is layer 7 of 7 in the OSI model. For example, email, Web browsing and video streaming applications reside at layer 7. See TCP/IP and OSI model.

While layers 1, 2, and 3 are mandatory for any data transmission, the application may use some unique interface layer to the application instead of the usual upper layers of the model.

According to the OSI Model, the session layer is where connections are established, managed, and torn down. For connection-oriented network protocols, understanding how the session layer works ...