In the OSI model, which layer is mainly concerned with the raw transmission of bits over a physical medium?

• A. Physical Layer (Layer 1)
• B. Data Link Layer (Layer 2)
• C. Network Layer (Layer 3)
• D. Transport Layer (Layer 4)

Answer: (A)

The key idea here is understanding where raw bit signaling lives in the OSI model. The layer that handles the actual transmission of bits over a physical medium is the Physical Layer. It deals with the hardware aspects of sending electrical, optical, or radio signals—the cables or air, the connectors, voltage levels, timing, and signaling methods. It’s about turning data into a stream of bits and getting those bits onto the wire, ready for the next layer to frame and manage.

The Data Link Layer, in contrast, takes those bits and formats them into frames, handles MAC addressing and error detection, and manages access to the physical medium. The Network Layer moves packets between networks with routing and logical addressing. The Transport Layer focuses on end-to-end communication, reliability, and flow control.