A network with a central switch forms a star topology.
In computer networks, a switch - also known as a network switch or distributor - is a coupling element that connects network segments with each other. Within a segment (broadcast domain), it ensures that the data packets, so-called "frames", reach their destination. Unlike a repeater hub, which appears very similar at first glance, frames are not simply forwarded to all other ports, however, but only to the one to which the target device is connected - a switch makes a forwarding decision on the basis of the automatically learned hardware addresses of the connected devices.
The term switch generally refers to a multiport bridge - an active network device that forwards frames based on information from the Data Link Layer (Layer 2) of the OSI model. Sometimes the more precise terms bridging hub or switching hub are used; in the IEEE 802.3 standard, the function is called MAC bridge. (Packet) "Switching" is borrowed from circuit-switching technology, in fact nothing is "switched". The first EtherSwitch was introduced by Kalpana in 1990.
The device comparable to the switch on network layer 1 (Layer 1) is called a (repeater) hub. Switches that additionally process data on the network layer (Layer 3 and higher) are often referred to as Layer 3 switches or multilayer switches and can fulfill the function of a router. In addition to Ethernet switches, there are Fibre Channel switches, and SAS expanders are also increasingly referred to as switches. Fibre Channel (FC) defines a non-routable standard protocol from the field of storage networks, which was designed as a variant of SCSI for the high-speed transfer of large amounts of data. SAS (Serial Attached SCSI) is the direct successor to the older parallel SCSI interface.