Application Layer of the Internet Protocol

The final, topmost layer of the Internet Protocol suite.

Data at the Application Layer

The Application Layer is where we get to the protocols that describe the behaviour of applications. All the preceding lower levels are effectively plumbing that enables applications to do the things they want accross the internet.

Whereas the lower levels facilitate communication accross the internet, the Application Layer is concerned with achieving a specific task once the ability to communicate is assured.

Application Layer protocols include HTTP, the Simple Mail Transfer Protocol (SMTP), and FTP.

c301a0b3_Mosaic_Netscape_and_Browser_Wars
- It became the best of the early browsers (a group that included ViolaWWW and Erwise) with the notable advantage of being able to embed graphics alongside text (instead of inside a separate window). It also supported multiple application layer protocols - FTP, the Network News Transfer Protocol, Gopher - not just HTTP.
Internet fundamentals
- The Application Layer concerned with software that utilises information received and sent over the internet, for instance web pages and emails. This is the highest level of abstraction for which all the lower levels serve as “plumbing”. Examples of protocols operative at the Application Layer include HTTP and SSH.
Example scenario of data transfer accross the internet
- The web browser knows HTTP - a protocol of the Application Layer - and forms an HTTP request intended for the destination server.