Layer transmits raw bits over physical media. Data becomes voltage, light pulses, or radio waves.
Main concerns:
- Media types: copper, fiber optic, wireless
- Signaling: how s and s are encoded
- Bit rate: bits per second
- Connectors: RJ-45, fiber connectors, antennas
Layer devices include hubs and repeaters. They repeat signals without understanding addresses. Problems here are physical: damaged cables, loose connectors, interference.