OSI and TCP/IP Model

OSI and TCP/IP model
Introduction :
Most of us experience the Internet through the World Wide Web, e-mail services, and file-sharing programs. These applications, and many others, provide the human interface to the underlying network, enabling us to send and receive information with relative ease Typically the applications that we use are intuitive, 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 Open System Interconnection (OSI) model. In this chapter, we will focus on the role of one layer, the Application layer and its components: applications, services, and protocols. We will explore how these three elements make the robust communication across the information network possible.
In this chapter, you will learn to:
• Describe how the functions of the three upper OSI model layers provide network services to end user applications.
• Describe how the TCP/IP Application Layer protocols provide the services specified by the upper layers of the OSI model.
• Define how people use the Application Layer to communicate across the information network.
• Describe the function of well-known TCP/IP applications, such as the World Wide Web and email, and their related services (HTTP, DNS, SMB, DHCP, STMP/POP, and Telnet).
• Describe file-sharing processes that use peer-to-peer applications and the Gnutella protocol.
• Explain how protocols ensure services running on one kind of device can send to and receive data from many different network devices.