Which layer in the OSI model is responsible for providing network services to end-user applications?

• A. Application Layer
• B. Data Link Layer
• C. Physical Layer
• D. Network Layer

Answer: (A)

The key idea is which layer directly offers the network-facing services that end-user applications use. The Application Layer sits at the top of the OSI model and provides protocols and services that applications rely on to communicate over a network—think HTTP for web pages, SMTP for email, FTP for file transfer, DNS for name resolution, and similar interfaces. It translates user requests into network data and presents received data to applications in a usable form, handling things like data representation and user-facing services.

The other layers handle the mechanics of transmission rather than providing services to applications. The Data Link Layer takes care of framing, error detection, and access to the local link. The Physical Layer deals with the actual electrical, optical, or radio signals and hardware. The Network Layer handles routing and addressing to move packets between networks. Because they don’t offer direct services to end-user applications, they aren’t the layer described in the question.