Which layers comprise the TCP/IP model?

• A. Application, Transport, Internet, Network Interface
• B. Physical, Data Link, Network, Transport, Application
• C. Presentation, Session, Transport, Internet
• D. Data Link, Physical, Network, Session

Answer: (A)

Understanding TCP/IP means recognizing its four-layer structure: Network Interface (also called Link), Internet, Transport, and Application. This setup aligns with how protocols are organized and used in networking today. At the bottom, the Network Interface layer handles how data is transmitted on a physical network, integrating the responsibilities of the OSI Physical and Data Link layers. Above that, the Internet layer provides addressing and routing (IP). The Transport layer handles end-to-end delivery using protocols like TCP and UDP. Finally, the Application layer contains high-level protocols used by applications, such as HTTP, FTP, and DNS. This four-layer arrangement is what TCP/IP specifies, which is why this option lists exactly those layers. Other options mix in OSI-specific layers such as Presentation or Session, or separate Physical and Data Link into distinct layers, which does not match TCP/IP's four-layer model. The layers, from bottom to top, are Network Interface, Internet, Transport, Application.