A switch is a network device that selects a path or circuit for sending a unit of data to its next destination. A switch may also include the function of the router, however, a switch is more simplistic in function. Switches are great, they add network capacity and speed, but they are not a cure-all. .
Switches occupy the same place in the network as hubs. Switches examine each packet and process it accordingly rather than simply repeating the signal to all ports. Switches map the Ethernet addresses of the nodes residing on each network segment and then allow only the necessary traffic to pass through the switch. When a packet is received by the switch, the switch examines the destination and source hardware addresses and compares them to a table of network segments and addresses. If the segments are the same, the packet is dropped or "filtered"; if the segments are different, then the packet is "forwarded" to the proper segment. Additionally, switches prevent bad or misaligned packets from spreading by not forwarding them.
Filtering of packets, and the regeneration of forwarded packets enables switching technology to split a network into separate collision domains. Regeneration of packets allows for greater distances and more nodes to be used in the total network design, and dramatically lowers the overall collision rates. In switched networks, each segment is an independent collision domain. In shared networks all nodes reside in one, big shared collision domain. .
A switch performs the work of a hub, except that it registers the IP addresses of the computers plugged into it and while a hub transfers packets to every computer on the network and a switch only transfers data to specific computers. When it receives a message, it only sends it to the intended recipient. Switches cut down on unnecessary traffic broadcasts and allow you to have an affordable high-performance network. A switch also corrects traffic jam problems by ensuring that data goes straight from its origin to its proper destination, with no wandering in-between.