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A leased line is a private bidirectional or symmetric telecommunications line between two or more locations provided in exchange for a monthly rent. Sometimes known as a private circuit or data line in the UK. Unlike traditional PSTN lines it does not have a telephone number, each side of the line being permanently connected to the other. Leased lines can be used for telephone, data or Internet services. Some are ringdown services, and some connect to a Private branch exchange. Typically, leased lines are used by businesses to connect geographically distant offices. Unlike dial-up connections, a leased line is always active. The fee for the connection is a fixed monthly rate. The primary factors affecting the monthly fee are distance between end points and the speed of the circuit. Because the connection does not carry anybody else's communications, the carrier can assure a given level of quality. An Internet leased line is a premium internet connectivity product, delivered over fiber normally, which is dedicated and provides uncontended, symmetrical speeds, full-duplex. It is also known as an ethernet leased line, DIA line, data circuit or private circuit. For example, a T-1 channel can be leased, and provides a maximum transmission speed of 1.544 Mbit/s. The user can divide the connection into different lines for multiplexing data and voice communication, or use the channel for one data circuit. Leased lines, as opposed to DSL, are being used by companies and individuals for Internet access because they afford faster data transfer rates and are cost-effective for heavy users of the Internet. ==History== Leased lines services (or private line services) became digital in the 1970s with the conversion of the Bell backbone network from analog to digital circuits. This allowed AT&T to offer Dataphone Digital Services (later re-branded digital data services) that started the deployment of ISDN and T1 lines to customer premises to connect.〔Microsoft Encyclopedia of Networking, Second Edition. Microsoft Press. © 2002.〕 Leased lines were used to connect mainframe computers with terminals and remote sites, via IBM Systems Network Architecture (created in 1974) or DECnet (created in 1975). With the extension of digital services in the 1980s leased lines were used to connect customer premises to Frame Relay or ATM networks. Access data rates increased from the original T1 option up to T3 circuits. In the 1990s with the advances of the Internet, leased lines were also used to connect customer premises to ISP Point of Presence whilst the following decade saw a convergence of the aforementioned services (frame relay, ATM, Internet for businesses) with the MPLS integrated offerings. Access data rates also evolved dramatically to speeds of up to 10Gbit/s in the early 21st century with the Internet boom and increased offering in long-haul optical networks or Metropolitan Area Networks. 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「leased line」の詳細全文を読む スポンサード リンク
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