A Network Hub is a telecommunication device which facilitates communication within networks. It is classified as a layer-one device on the OSI model. It does not discriminate or selectively forward connections, but simply repeats all communication on all ports. This enables basic networking, but can result in greatly reduced efficiency, since there can be many collisions. Also, they offer no network security, since any device connected to a hub can receive data from and communicate with any other device on that hub or any hub connected to it. Hubs are now obsolete—they have been almost entirely replaced with switches.
Passive vs. active
The first kind of hub was passive. This meant that they were unpowered devices, which simply connected data lines. However, this was a drain on the cabling, since signals could be significantly weakened when split up across multiple lines. Therefore, active hubs were soon introduced, which transmitted duplicate signals using their own power. This dramatically increased the number of supported devices and the wiring range.