We experience the Internet through the World Wide Web, email services, and file-sharing programs. These applications, and many others, provide the human interface to the underlying network, enabling us to send and receive data with relative ease. Typically the applications that we use are intuitive and transparent, meaning we can access and use them without knowing how they work. However, for network professionals, it is important to know how an application is able to format, transmit and interpret messages that are sent and received across the network.
Visualizing the mechanisms that enable communication across the network is made easier if we use the layered framework of the OSI model.
In this chapter, we will explore the role of the application layer and how the applications, services, and protocols within the application layer make robust communication across data networks possible.