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Switch is a device that filters and transmits data packets in a network. A switch is like a lever or a button. Switches operate at level 2 (data link layer) or sometimes at level 3 (network layer) of the OSI model and hence can support any protocol. Local Area Networks that use switches to join segments are called switched LANs.
A switch keeps track of the machine addresses of all the devices attached to it. By this it knows as to which device belongs to which port and controls the flow of traffic data. Switches learn the location of devices connected instantaneously. When a frame arrives, the switch is aware which port it has to send it to, thereby reducing the network response time. The trip from a switching point to another in a network is termed as hop and the time it takes to decide where to transmit the data packet is called its latency. Latency is the price paid for the flexibility that switches bring to the network. A switch allocates the full bandwidth to each of its port. In this way, the users always the get the maximum speed available. Hence a switch is considered better than a hub (bandwidth is shared among its ports) in terms of performance of the device. Switches are located at the gateway levels of a network, where one network can connect to another (core switches) or at the sub network level where data is transmitted near to its origin or destination (desktop switches).
Switch is generally required for large networks (about more than 50 users). Switches can also be connected to each other in order to increase the number of devices connecting to the LAN. Different models of switches are available depending on the number of connecting devices.
Ethernet switches are the most common type of switches used in networks and have four to eight connections, while corporate switches support as high as 32 to 128 connections.