Layers of Network Communication
Communication between a client application and a server application happens in three levels:
Hardware level
Operating system level
Application level Hardware level: The physical connection might be wireless or network cables, phone lines or TV cable. For the local wired or wireless networks, a network adapter inside your computer is part of the physical network. Communication rules are predetermined and these rules are called protocols. Each network adapter is assigned a MAC address, and this address is used to uniquely identify a computer on a local network.
Operating system level: The Operating system is responsible for managing communication between itself and another computer, using rules for communication that both operating systems understand. This would be known as the TCP/IP Protocol. Where on OS address another OS called IP addresses.
Application level: The application level is when you use the internet to surf the web or emailing, you are using a application on your computer called Internet client. This would be done through a browser, like Internet Explore, Google Chrome, or Firefox. When you open a browse you are communicating with another application somewhere on the Internet, called a server. An application on the server would be like email server or a web server. The client and server applications are each assigned a number that uniquely identifies the application on the computer. This is called a port number, port, or port address.
When you connect the computer to a network, the communication must work on all 3 levels.
(Andrews 2014)
(Microsoft 2015)