Where is a hub specified in the OSI model?

A hub operates at the Physical layer of the OSI model, which is the first layer. This layer is responsible for the actual transmission of raw data bits over a physical medium. A hub functions as a basic networking device that connects multiple Ethernet devices, making them act as a single network segment. It receives incoming data packets on one port and retransmits them out all other ports without any filtering or processing, thus operating purely at the physical level.

The Physical layer encompasses the hardware aspects of networking, including the cables, switches, network interface cards, and hubs. Its primary focus is on the medium of transmission and the signals used for communication, ensuring that data can physically travel between devices. This is why the role of a hub is clearly defined at this layer, distinct from the functions of the other layers in the OSI model, which handle more complex processing and data handling tasks.