What does the Physical layer of the OSI model primarily deal with?

The Physical layer of the OSI model primarily deals with the actual physical connection between devices, focusing on the transmission and reception of unstructured raw data over a physical medium. This includes aspects such as electrical signals, light signals (for fiber optics), and the physical layout of cables, connectors, and networking hardware. The emphasis is on how data bits are transmitted over various media, including specifications for voltage levels, timing of voltage changes, physical data rates, and the physical interface with the transmission medium.

The other choices pertain to different layers of the OSI model. Session control is a function of the Session layer, which manages sessions and controls the dialogues between computers. Data formatting is associated with the Presentation layer, where data is translated into a format that can be understood by the application layer. Application interfaces relate to the Application layer, which provides end-user services and network applications. Thus, the focus on data transmission methods makes the first choice the most relevant to the Physical layer.