Layer 1 example

• A. Physical cables, hubs, or signals
• B. Firewall appliances
• C. Switch
• D. Router

Answer: (A)

Layer 1 is about the physical transmission of raw bits over a medium. It defines the actual hardware and signaling used to move data: the cables and connectors, and the electrical or optical signals that carry the data. A hub fits here because it simply repeats the incoming electrical signal to all ports without interpreting the data, so it operates at the physical layer. In contrast, switches, routers, and firewalls work at higher layers (switches at Layer 2, routers at Layer 3, firewalls at various higher layers). Therefore the example that represents Layer 1 is physical cables, hubs, or signals.