Which of the following is the highest layer used for data transmission when using Telnet or FTP?

The highest layer used for data transmission when using Telnet or FTP is the Application layer. In the OSI model, the Application layer is the one that directly interacts with end-user applications to provide network services. It enables applications to communicate over a network and defines protocols for specific data transmission tasks.

Telnet and FTP are both protocols that operate at this Application layer, facilitating user interaction with remote systems and file transfers, respectively. They serve functions essential to user engagement and application-level requirements in networking.

The Presentation and Session layers, while important, serve different purposes. The Presentation layer is responsible for data formatting and encryption, ensuring data is in a usable format, but does not handle data transmission directly. The Session layer manages sessions and controls the dialogues between computers but is not the highest layer for the protocols in question. The Transport layer focuses on the end-to-end communication and may handle reliability and flow control but is also not where Telnet and FTP operate primarily. Thus, the Application layer stands out as the correct answer in this context.