The Three Lower Layers of the OSI Model: Physical, Data Link, and Network

1. Physical Layer (Layer 1)

Transmits raw bits over media (copper, fiber, wireless). Defines electrical/optical encoding, modulation, synchronization, connectors, topology.

2. Data Link Layer (Layer 2)

Reliable node-to-node transfer. Framing, error detection, flow control, MAC addressing. Protocols: Ethernet, Wi-Fi, PPP.

3. Network Layer (Layer 3)

Routing and logical addressing (IP). Path determination, congestion control, internetworking. Protocols: IP, ARP, ICMP.