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Trunk Line Four. Ultra high speed digital transmission line offering a total data-carrying capacity (bandwidth) of 274.176 million bits per second (Mbps) with 4,032 individual channels in the US version, 97.728 Mbps with 1,440 channels in the Japanese (J-4) version, and 139.264 Mbps with 1,920 channels in the European (E-4) version. T-4 and its variants require coaxial or fiber-optics cables or radio (microwave) media and cannot run on ordinary (unshielded twisted pair) telephone lines.

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