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)