Switch is a device which combines separate LAN segments and provides packet filtering between them. The LAN switch is a device with count of ports, each of which may cooperate with the Ethernet network. Although they provide the same opportunities to connect with network cables as hubs, it is better to the extent that they increase the efficiency of the whole network. This is so as a result of the extension of data bandwidth (maximum capacity of data networks). Instead of sharing the entire available bandwidth among all users, as in the case of a hub, switch assigns each connected network device specific part of the band. For example, each hub 10 Mb / s will make the whole bandwidth of 10 Mb/s to all connected devices. A corresponding switch will assign the bandwidth to each device individually, which will significantly increase productivity. A further increase in efficiency can be achieved by introducing switches which allow you to handle bi-directional connections. An operation of switches is based on possibility of storing the MAC address of each machine on the local area network and information about which port communicates with the device. Switches resemble hubs (ang. Hub), but unlike them, the incoming data are addressed only to the port on which the device to which the packet is addressed. Such action is possible due to the fact that the switch "learns" the MAC addresses of devices connected to it. Associations, MAC address - physical port, are stored in the device memory which could normally accommodate 4096, 8192 or 16384 entries (array of size 4KB, 8KB or 16KB).
Switches collision domain are limited to one port. Therefore, unlike hubs, switches operate in full-duplex mode which allows for simultaneous transmission of data in both directions. Also, switches enable the creation of virtual LANs or network logically separated from larger physical network. Virtual Network allows you to group different devices regardless of their physical location. VLAN is created by assigning the appropriate switch ports. One port can belong to only one virtual network. Frames in virtual networks are marked accordingly, so that the switch "knows" to which ports can be forwarded.
The most sold switches have 4, 5, 8, 16, 24 or 48 ports.