What does the Physical Layer (Layer 1) do with messages?

The Physical Layer, also known as Layer 1 of the OSI model, is responsible for the transmission and reception of raw bitstreams over a physical medium. This layer deals with the physical means of sending data, including the hardware technologies required to transmit those bits. When a message is prepared for transmission, the Physical Layer converts that message into a series of bits, which are then transmitted over communication channels like cables, optical fibers, or wireless signals.

This process involves taking higher-level data and encoding it into binary format (0s and 1s) that can be sent across the physical medium. The focus of the Physical Layer is purely on the physical aspects of data transmission—ensuring that the bits are effectively transmitted rather than interpreting the content or meaning of them.

In contrast, other functions like transforming data into a readable format occur at higher layers, such as the Presentation Layer, while establishing sessions and ensuring data integrity through error checking are handled by the Session Layer and Transport Layer, respectively. Thus, the role of the Physical Layer is specifically tied to the conversion of messages into bits, making option B the correct choice.