In this article we will discuss Application Layer, will make brief discussion on Application Layer, In last article we discuss about UDP Datagram Reassembly.
The application layer is closest to the end user. As shown in the figure, it is the layer that provides the interface between the applications used to communicate and the underlying network over which messages are transmitted. Application layer protocols are used to exchange data between programs running on the source and destination hosts. An application layer is an abstraction layer that specifies the shared communications protocols and interface methods used by hosts in a communications network.
The upper three layers of the OSI model (application, presentation, and session) define functions of the single TCP/IP application layer. The application layer abstraction is used in both of the standard models of computer networking: the Internet Protocol Suite (TCP/IP) and the OSI model. Application layer security refers to methods of protecting Web applications at the application layer (layer 7 of the seven-layer OSI model) from malicious attacks that may expose private information. Security is applied to the application layer specifically to protect against unauthorized access and attacks.
There are many application layer protocols, and new protocols are always being developed. Some of the most widely known application layer protocols include Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), Trivial File Transfer Protocol (TFTP), Internet Message Access Protocol (IMAP), and Domain Name System (DNS) protocol.