What layer divides the bit stream received from the network layer into manageable data units called frames?

The layer responsible for dividing the bit stream received from the network layer into manageable data units called frames is the data link layer, also known as Layer 2. This layer plays a crucial role in the communication process by structuring the data into frames and managing how data packets are sent over the physical medium.

Layer 2's functions include addressing (by adding physical addresses to frames), error detection, and frame synchronization. By organizing data into frames, Layer 2 ensures that it can be transmitted efficiently and recognized properly by devices on the same local area network. Each frame contains not only the actual data being transmitted but also control information that helps with the delivery of that data to its intended destination.

In contrast, Layer 1, known as the physical layer, deals with the raw transmission of bits over a physical medium but does not structure these bits into frames; it focuses purely on the electrical and physical representation of the data. Layer 3, the network layer, is focused on routing and forwarding packets between different networks rather than framing data. Layer 4, the transport layer, is responsible for end-to-end communication and typically involves segmenting data for flow control and error recovery but does not handle converting the bit stream into frames.