A networking switch is the central device in a wired or wireless local area network (LAN). It receives signals from each computer on the network via Ethernet cables in a wired network or radio waves in a wireless LAN. In both cases, the switch directs traffic across the LAN, enabling the computers to talk to each other and share resources.
All computers included in the LAN must contain a network interface card (NIC). The card assigns a unique address to the machine in which it is installed. This address is called a Medium Access Control (MAC). A wired NIC accommodates an Ethernet cable, which runs to a port on the back of the networking switch. If the NIC is wireless, the card will feature a small antenna transmits signals to the wireless switch, which also bears an antenna rather than ports. Whether wireless or wired, the switch acts as a relay, reading traffic packets as they arrive from the various machines and directing the packets to the proper MAC address.
A networking switch runs in full-duplex mode, meaning a machine on the LAN can receive and transmit data at the same time. This is much faster than a networking hub, an alternate device that serves the same purpose but operates in half-duplex mode, allowing each machine or node either to send or receive at any given time. Another key difference between a switch and a hub is that the switch sends traffic discriminately, using addresses to direct traffic packets exactly where they are supposed to go. A networking hub, on the other hand, broadcasts all traffic on the network to all nodes, relying on filters within each machine to discard packets not addressed to it. This makes networks that use a hub particularly vulnerable to "packet sniffers" or eavesdropping.
For the above reasons, a networking switch is considered superior to a networking hub, but the device is also not foolproof. It can be "tricked" into accommodating packet sniffers, but the methods used to trick the switch will leave telltale traffic signatures, unlike the passive methods that can be used on a hub. Anti-sniffing software can be installed on a switched network to detect packet sniffers.
Network switches are inexpensive devices, but the do increase in price with the number of ports featured. For those with cable modem or DSL service, a broadband router with a built-in switch and firewall can be used in lieu of a stand-alone switch.