OSI and TCP model

Data networks and the Internet support the human network by supplying seamless, reliable communication between people - both locally and around the globe. On a single device, people can use multiple services such as e-mail, the web, and instant messaging to send messages or retrieve information. Applications such as e-mail clients, web browsers, and instant messaging clients allow people to use computers and networks to send messages and find information.
Data from each of these applications is packaged, transported, and delivered to the appropriate server daemon or application on the destination device. The processes described in the OSI Transport layer accept data from the Application layer and prepare it for addressing at the Network layer. The Transport layer is responsible for the overall end-to-end transfer of application data.
In this chapter, we examine the role of the Transport layer in encapsulating application data for use by the Network layer. The Transport layer also encompasses these functions:
• Enables multiple applications to communicate over the network at the same time on a single device
• Ensures that, if required, all the data is received reliably and in order by the correct application
• Employs error handling mechanisms