The physical layer is the bottom-most layer of OSI.

Its function is to transport data using electrical, mechanical or procedural interfaces. It is the closest layer to the physical connection between devices.

1. Sending raw data as bits over a physical medium.
2. Converting data into signals (encoding) and turning them back into data (decoding).
3. Ensuring signals are transmitted correctly.
4. Modulation.
5. Deciding how data flows through transmission modes, controlling the speed and timing of data transmission.
6. Synchronization.

• mesh topology;
• star topology;
• bus topology;
• ring topology;
• tree topology;
• hybrid topology.

• Simplex mode: only 1 node can transmit data and the other node receives data.
• Half-duplex mode: 2 nodes can send and receive data but not at the same time.
• Full-duplex mode: data can be sent and received from both nodes at the same time.

• Hubs
• Repeaters