network switch

What is a network switch:

• Switches operate at Layer 2 of the OSI Model, the Data-Link Layer. This is in contrast to routers, which operate at Layer 3 of the OSI Model, the Network Layer.
  
• A switch stores the MAC Address of every device which is connected to it.
  
• The switch will then evaluate every frame that passes through it. The switch will examine the destination MAC Address in each frame.
  
• Based upon the destination MAC Address, the switch will then decide which port to copy the frame to.
  
• If the switch does not recognize the MAC Address, it will not know which port to copy the frame to. When that happens, the switch will broadcast the frame to all of its ports.

Another Definition:
A network switch is a device that provides a switching function in a data communications network. Data communication in a computer network involves the exchange of data between two or more entities interconnected by communication links and sub-networks. A network switch is an intermediate station which interconnects the communication links and sub-networks to enable transmission of data between the end stations. Switching involves transferring information, such as digital data packets or frames, among entities of the network. A switch functions as an interchange and provides path switching for data being transported over a network. Typically, a switch supports one network protocol (e.g. Ethernet), meaning that the switch manages data in a particular format. Switched local area networks use a network switch for supplying data frames between network stations or other network nodes (such as routers or gateways), where each network node is connected to the network switch by a media. A network switch for routing packets between network buses includes a set of input switch ports for receiving packets arriving on the network buses, a set of output switch ports for forwarding packets outward on the network buses, and a switch fabric for routing packets between the input and output switch ports. Each input switch port includes a memory for storing packets arriving on a network until the switch fabric can forward them to an output switch port. The input port may convert each packet arriving on a network bus to a sequence of cells of uniform size which can be efficiently stored in uniformly-sized buffer memory storage locations until the input port can forward them in proper sequential order through the switch fabric to one of the switch's output ports. Each output switch port may also include a memory for storing packets it receives via the switch fabric until the port can forward them outward on a network bus. Each output switch port stores each cell sequence arriving from an input port in its own buffer memory. The output port later reassembles them into the packet from which they were derived, then forwards the packet outward on an another network bus.