Which layer in the OSI model handles application-level protocols like G-Mail and Outlook?

The layer in the OSI model that handles application-level protocols, such as those used by G-Mail and Outlook, is the seventh layer, known as the Application Layer. This layer is responsible for facilitating communication between software applications and the underlying network services. It provides functionalities such as file transfers, email services, and network services that enable user interactions with applications.

In the context of G-Mail and Outlook, these applications utilize protocols like SMTP (Simple Mail Transfer Protocol) for sending emails, IMAP (Internet Message Access Protocol), or POP3 (Post Office Protocol) for receiving emails. All of these functions occur at the Application Layer, where the user directly interacts with the application, and the layer manages the details of how data is presented to users.

The other layers mentioned do not focus on application-level protocols. For instance, the sixth layer is the Presentation Layer, which manages data formatting and encryption before the data reaches the Application Layer. The fifth layer is the Session Layer, which establishes, manages, and terminates sessions between applications, while the fourth layer is the Transport Layer, which handles data transfer and error recovery. Thus, the Application Layer is specifically designed to support user applications and their corresponding protocols, making it the correct choice.