A device that all lines on an Ethernet segment are plugged into. 10Base-T and 100Base-T Ethernets are star networks and require a hub for operation. The earlier 10Base5 and 10Base2 Ethernets are bus networks, but are often wired into a star configuration using a central hub for improved troubleshooting. A hub is also known as a "multiport repeater" and is sometimes called a "concentrator." See hub.