It is responsible for opening sessions, ensuring they remain open and functional while data is being transferred, and closing them when communication ends. The session layer creates communication channels, called sessions, between devices. The presentation layer takes any data transmitted by the application layer and prepares it for transmission over the session layer. It defines how two devices should encode, encrypt, and compress data so it is received correctly on the other end. The presentation layer prepares data for the application layer. A few examples of application layer protocols are the Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), Post Office Protocol (POP), Simple Mail Transfer Protocol (SMTP), and Domain Name System (DNS).
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It provides protocols that allow software to send and receive information and present meaningful data to users. The application layer is used by end-user software such as web browsers and email clients. We’ll describe OSI layers “top down” from the application layer that directly serves the end user, down to the physical layer. OSI was introduced in 1983 by representatives of the major computer and telecom companies, and was adopted by ISO as an international standard in 1984. However, the OSI 7-layer model is still widely used, as it helps visualize and communicate how networks operate, and helps isolate and troubleshoot networking problems. The modern Internet is not based on OSI, but on the simpler TCP/IP model. It was the first standard model for network communications, adopted by all major computer and telecommunication companies in the early 1980s The Open Systems Interconnection (OSI) model describes seven layers that computer systems use to communicate over a network.
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