What is SDLC and why is it important in software development?
Application Layer of OSI Model
The final topmost layer of the OSI (Open Systems Interconnection) model is called the Application Layer. It has an interface between the end user and the network and this enables the user to access network services directly via applications.
This layer is not the real software applications themselves (e.g. browsers or email clients) but the network services on which the software applications run and communicate over a network.
Key Functions of the Application Layer
User Interface to Network
It offers services that enable individuals to communicate with the networked applications, e.g. sending emails or reading web pages.
Network Services
Provides services such as file transfer, email, remote log-in and directory services.
Resource Sharing
Facilitates the ability to access the common network resources such as files, printers and servers.
Authentication and Authorization
Helps are used to verify user identity and to control access to network services.
Common Protocols at the Application Layer
HTTP/ HTTPS: Web communication protocol.
- FTP: Interchange of systems.
- SMTP: Sending emails
- POP3 / IMAP: Receiving emails
- DNS: Converts domain names into IP addresses.
- Telnet / SSH: remote log in and administration.
Example
The Application Layer interprets the HTTPS protocol or HTTP protocol when you enter a browser and request and receive web content in a server.
Application Layer: It is the layer that is involved in the provision of the network services to the user applications and, as such, is critical in communication between the users and the networked systems.
