T-1 Carrier

What Does T-1 Carrier Mean?

A T-1 carrier is a dedicated telephone connection or a time-division-multiplexed digital transmission service that supports a data rate of 1.544 Mbps. A T-1 line generally includes 24 separate channels, each of which is able to support 64 Kbps. Every 64 Kbps channel is often customized to transport voice or data traffic. The majority of telephone companies only allow the purchase of a few of the individual channels, referred to as fractional T-1 access.


The T-carrier systems are totally digital and use time-division multiplexing (TDM) and pulse code modulation (PCM). The original T carrier system was developed by Bell Labs in the early 1960s.

Techopedia Explains T-1 Carrier

T-1 is the method that is conventionally used by the telephone companies for transporting digitized telephone communication among central offices. Since the 1960s, a single T-1 channel was able to carry 24 high-quality voice conversations. Because T-1 is fully digital, it eradicates the chance of crosstalk, which is typical among analog carrier networks where the copper pairs tend to pick up transmissions from neighboring pairs.

A T-1 physically includes two twisted pairs of copper wire. The pairs use a full-duplex configuration in which one pair sends information while the other receives information.

There are two main framing standards used by a T-1 carrier line:

  • D4 framing is the main framing standard, which was primarily used in combination with T1 networks.
  • Another framing method used in T-1 is the relatively new Extended Super Frame (ESF). ESF makes use of fewer framing bits compared to D4 and offers the best way of obtaining performance data from T-1.

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Margaret Rouse

Margaret Rouse 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 explanations have appeared on TechTarget websites and she's been cited as an authority in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine and Discovery Magazine.Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages. If you have a suggestion for a new definition or how to improve a technical explanation, please email Margaret or contact her…