The Open Systems Interconnection (OSI) model defines seven layers through which computer systems communicate over a network. It was the first standard model for network communications, and it was adopted in the early 1980s by all major computer and telecommunications companies. 3.1 Describe how the 7 layers work together to ensure the integrity of data communication (5) 3.2 Describe the functions of each layer and their protocols. (10) 3.3 In networking it is important to follow steps before we talk about TCP/IP protocol stack and IP addressing we must know the difference between binary, decimal, and hexadecimal numbers and how we convert from one format to the other.