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The T-carrier is a member of the series of carrier systems developed by AT&T Bell Laboratories for digital transmission of multiplexed telephone calls. The first version, the Transmission System 1 (T-1), was introduced in 1962 in the Bell System in North America, and could transmit up to 24 telephone calls simultaneously over a single transmission line of copper wire. Subsequent specifications carried multiples of the basic T1 (1.544 Mbit/s) data rates, such as T2 (6.312 Mb/s) with 96 channels, T3 (44.736 Mb/s) with 672 channels, and others. ==Transmission System 1== T-1 is a hardware specification for telecommunications trunking. A ''trunk'' is a single transmission channel between two points on the network: each point is either a switching center or a node (such as a telephone). Initially, T-1 trunks were used only to connect major telephone exchanges, via the same twisted pair copper wire that the analog trunks used. If the exchanges were too far apart, a repeater boosted the signal. Before the digital T-1 system, carrier systems such as 12-channel carrier systems worked by frequency division multiplexing; each call was an analog signal. A T-1 trunk could transmit 24 telephone calls at a time, because it used a digital carrier signal called Digital Signal 1 (DS-1).〔J.R. Davis, A. K. Reilly, T-Carrier Characterization Program – Overview, Bell System Technical Journal July–August 1981, Vol 60 No 6 Part 1〕 DS-1 is a communications protocol for multiplexing the bitstreams of up to 24 telephone calls, along with two special bits: a ''framing bit'' (for frame synchronization) and a ''maintenance-signaling bit''. T-1's maximum data transmission rate is 1.544 megabits per second. Throughout Europe and most of the rest of the world there is a comparable transmission system called E-carrier, which is not directly compatible with T-carrier. 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「T-carrier」の詳細全文を読む スポンサード リンク
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