Which of the following is NOT a layer in the OSI model?

The OSI (Open Systems Interconnection) model comprises seven layers: Application, Presentation, Session, Transport, Network, Data Link, and Physical. The layers are designed to facilitate communication between different networking systems and to support a variety of protocols.

The Application layer refers to the closest layer to the end user, which facilitates user interactions with the network services. The Network layer is responsible for routing and forwarding data packets, and the Transport layer ensures reliable data transmission, providing error recovery and flow control.

"Data Transmission" does not represent an official layer within the OSI model; it is a general term that could refer to various activities or methods involved in transferring data over a network. The absence of "Data Transmission" from the OSI model highlights that this term does not align with any specific infrastructure layer identified within the standard framework. Therefore, the correct choice indicates a lack of recognition of "Data Transmission" as a layer in the OSI model.