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A network switch (also called switching hub, bridging hub, officially MAC bridge〔IEEE 802.1D〕) is a computer networking device that connects devices together on a computer network, by using packet switching to receive, process and forward data to the destination device. Unlike less advanced network hubs, a network switch forwards data only to one or multiple devices that need to receive it, rather than broadcasting the same data out of each of its ports. A network switch is a multiport network bridge that uses hardware addresses to process and forward data at the data link layer (layer 2) of the OSI model. Switches can also process data at the network layer (layer 3) by additionally incorporating routing functionality that most commonly uses IP addresses to perform packet forwarding; such switches are commonly known as layer-3 switches or multilayer switches. Beside most commonly used Ethernet switches, they exist for various types of networks, including Fibre Channel, Asynchronous Transfer Mode, and InfiniBand. The first Ethernet switch was introduced by Kalpana in 1990. == Overview == A switch is a device in a computer network that electrically and logically connects together other devices. Multiple data cables are plugged into a switch to enable communication between different networked devices. Switches manage the flow of data across a network by transmitting a received message only to the one or more devices for which the message was intended. Each networked device connected to a switch can be identified using a MAC address, allowing the switch to regulate the flow of traffic. This maximizes the security and efficiency of the network. Essentially, when replacing a repeater hub with an Ethernet switch, the single large collision domain is split up into smaller ones, reducing the probability and scope of collisions and, as a result, increasing the potential throughput. Because broadcasts are still being forwarded to all connected devices, the newly formed network segment continues to be a broadcast domain. Due to these features, a switch may be seen as more "intelligent" than a repeater hub, which simply retransmits messages out of every port of the hub but the receiving one, unable to distinguish different recipients, and greatly degrading the overall efficiency of the network. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「network switch」の詳細全文を読む スポンサード リンク
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