Switch

A mechanical, electrical or electronic device which opens or closes circuits, completes or breaks an electrical path, or select paths or circuits. Switches work at Layers 1 (Physical) and 2 (Data Link) of the OSI Reference Model, with emphasis on Layer 2. A switch looks at incoming data (voice data, or data data) to determine the destination address. Based on that address, a transmission path is set up through the switching matrix between the incoming and outgoing physical communications ports and links. Data switches (e.g., LAN (Local Area Network) switches and packet switches) also typically contain buffers, which can hold data packets in temporary memory until the necessary resources are available to allow the data packets to be forwarded. Voice switches, of course, don't, because you can't delay voice. Switches work link-by-link, with multiple switches typically being involved in complex networks; each switch forwards the data on a link-by-link (hop-by-hop) basis. Routers are highly intelligent data switches which are capable of setting up paths from end-to-end, perhaps in consideration of the level of privilege of the user and application. Routers commonly are used at the edges of complex data networks, where intelligence is required to set up appropriate network paths. Although such intelligent decisions impose some delay on the packet traffic, they are made only at the ingress and egress edges of the network. The routers often instruct switches in the core of the network, where speed is of the essence-switches aren't as intelligent as routers, but they are faster and less expensive.