Which OSI layer is primarily concerned with encoding and modulation of signals on the transmission medium?

• A. Physical Layer (Layer 1)
• B. Data Link Layer (Layer 2)
• C. Network Layer (Layer 3)
• D. Application Layer (Layer 7)

Answer: (A)

Encoding and modulation of signals on the transmission medium are handled by the Physical Layer. This layer defines how raw bits are represented as electrical, optical, or radio signals and how those signals are modulated for transmission over the medium. It covers the actual physical connection, signal levels, timing, and the encoding schemes used to place bits onto the wire or fiber. The other layers build on this: the Data Link Layer groups bits into frames and manages access and error detection, the Network Layer handles routing, and the Application Layer deals with user processes. So the task of converting digital data into the physical signals that travel over the medium sits with the Physical Layer.