Which device operates ONLY at the Physical Layer?

Which device operates ONLY at the Physical Layer?

• A. Router
• B. Switch
• C. Network Hub
• D. Firewall

Answer: (C)

The correct choice is the network hub, which operates exclusively at the Physical Layer of the OSI model. The Physical Layer is responsible for the transmission and reception of raw binary data over a physical medium, such as cables or fiber optics. A hub functions as a basic networking device that connects multiple Ethernet devices, making them act as a single network segment. In contrast, a router operates at the Network Layer, where it makes decisions about the routing of packets between different networks. A switch operates primarily at the Data Link Layer, as it uses MAC addresses to forward data to specific devices within a local area network (LAN). A firewall operates at multiple layers, often including the Network and Transport Layers, to inspect and filter traffic based on predefined security rules. Therefore, the network hub is the only option that is limited to the Physical Layer, making it distinct from the other devices that operate at higher levels in the OSI model.

The correct choice is the network hub, which operates exclusively at the Physical Layer of the OSI model. The Physical Layer is responsible for the transmission and reception of raw binary data over a physical medium, such as cables or fiber optics. A hub functions as a basic networking device that connects multiple Ethernet devices, making them act as a single network segment.

In contrast, a router operates at the Network Layer, where it makes decisions about the routing of packets between different networks. A switch operates primarily at the Data Link Layer, as it uses MAC addresses to forward data to specific devices within a local area network (LAN). A firewall operates at multiple layers, often including the Network and Transport Layers, to inspect and filter traffic based on predefined security rules.

Therefore, the network hub is the only option that is limited to the Physical Layer, making it distinct from the other devices that operate at higher levels in the OSI model.