The Internet has become an integral part of our lives, with a wide range of applications such as file transfer, email sending, online video, web browsing, and online gaming. Because of the layered network model, common users can use various services provided by the application layer, without knowing technical details such as communication technology implementations. In previous courses, we have learned technologies related to the data link layer, network layer, and transport layer. This chapter will describe common network services and applications such as FTP, DHCP, and HTTP.