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What Does T-Carrier Mean?

The T-carrier system is a fully digital transmission system developed by Bell Labs and introduced in the US in 1962 with the T-1 line, which supported digitized voice transmission through pulse code modulation (PCM) and time-division multiplexing (TDM), which greatly increased the number of telephone calls that a given telephone network was capable of handling at one time.


Techopedia Explains T-Carrier

T-carrier systems are commonly used by telecommunications companies, most commonly the T-1 line, with a transfer rate of 1.544 Mbps, and the T-3 line, with a transfer rate of 44.736 Mbps, for providing Internet access to homes and businesses. The T-carrier system makes use of four wires: a pair is used for receiving data and the other pair is for transmission, making it a full-duplex transmission system.

The T-1 digital stream is made up of twenty-four 64-Kbps channels, which are further multiplexed. The four wires being used for the T-1 system originally made use of twisted pair wires, but now some variations make use of coaxial cables or even optical fiber.

T-carrier technology was already in use in the US by 1962, but it was not until 1983 that AT&T introduced it to the general public as a communications product, which was initially aimed at voice data but increasingly found use in general data transmission. Because of its good qualities, T-carrier technology is still being used today by Internet service providers (ISPs), specifically the T-1 and the T-3 lines.

Variations of the T-carrier system are as follows:

  • T-1: 24 channels and 1.544 Mbps of bandwidth
  • T-2: 96 channels and 6.312 Mbps of bandwidth
  • T-3: 432 channels and 44.736 Mbps of bandwidth
  • T-4: 4032 channels and 274.176 Mbps of bandwidth

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Margaret Rouse
Senior Editor
Margaret Rouse
Senior Editor

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.