The top layer of OSI model is the application layer. This layer is created for translating software or application commands and requests to language familiar to low-layer network services. The software sends security, procedural, synchronization requirements. Some of the requirements that can not be executed by Application layer are being forwarded down the OSI, while others being executed.
Figure 1. Application layer in OSI Networking Model
Simplest example of Application protocol is the HTTP (Hypertext Transfer Protocol) used in all modern Web Browsers. When user wants to access web page, browser is sending request to HTTP which makes connection with web server. Then the request of specific web page is being sent. In unlucky scenario of wrong page name or if user does not have permission to access the page, server would respond with an error message. Otherwise, if page is available and user has all the necessary permissions to access it, the browser would get response through the HTTP protocol. The response would contain the web page version applicable for users specific browser with all the information, that would be converted to readable format by the web browser. As it has been noted before, the Application layer on user workstation communicates only with the same layer on the server.
