A hub is a small rectangular box, often made of plastic, that receives its power from an ordinary wall outlet. A hub joins multiple computers (or other network devices) together to form a single network segment. On this network segment, all computers can communicate directly with each other. Hub, sometimes referred to as a concentrator or repeater Hub,acts as a convergence point of a Network, allowing the transfer of data packets.
Ethernet hubs are by far the most common type, but hubs for other types of networks such as USB also exist.
Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports. When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets. In other words, a hub works by duplicating the data packets received via one Port, and making it available to all ports, therefore allowing data sharing between all devices connected to the hub. Larger hubs contain eight, 12, 16, and even 24 ports.
Hubs classify as Layer 1 devices in the OSI model. At the physical layer, hubs can support little in the way of sophisticated networking. Hubs do not read any of the data passing through them and are not aware of their source or destination. Essentially, a hub simply receives incoming packets, possibly amplifies the electrical signal, and broadcasts these packets out to all devices on the network – including the one that originally sent the packet.
TYPES OF HUBS:
A passive hub serves simply as a conduit for the data, enabling it to go from one device (or segment) to another.Passive hubs do not amplify the electrical signal of incoming packets before broadcasting them out to the network.
Active hubs do perform this amplification, as does a different type of dedicated network device called a repeater.
MANAGEABLE HUBS/ INTELLIGENT HUBS
Intelligent hubs include additional features that enables an administrator to monitor the traffic passing through the hub and to configure each port in the hub. The intelligent hub typically is stackable (built in such a way that multiple units can be placed one on top of the other to conserve space). It also typically includes remote management capabilities via SNMP and virtual LAN (VLAN) support.
The switching hub actually reads the destination address of each packet and then forwards the packet to the correct port.