Editing T-carrier (section)

{{short description|Carrier system for digital transmission of multiplexed telephone calls.}}
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[[File:Network Interface Unit.jpg|thumb|right|Left: A [[66 block]]; center and right: Cabinets containing [[Smartjack]] [[network interface device]]s for T1 circuits]]

The '''T-carrier''' is a member of the series of [[carrier system]]s developed by AT&T [[Bell Labs|Bell Laboratories]] for [[digital transmission]] of [[multiplexed]] [[telephone call]]s.

The first version, the '''Transmission System 1''' ('''T1'''), was introduced in 1962 in the [[Bell System]], 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&nbsp;Mbit/s) data rates, such as T2 (6.312&nbsp;Mbit/s) with 96 channels, [[Digital Signal 3|T3]] (44.736&nbsp;Mbit/s) with 672 channels, and others.

Although a ''T2'' was defined as part of AT&T's T-carrier system, which defined five levels, T1 through T5,<ref name=TxDefs.net>{{cite web
   |url=https://r12hiw.netlify.app/t1-t2-t3-speed-comparisons.html
   |title=T1 T2 T3 Speed Comparisons|date=11 January 2020}}</ref> only the T1 and T3 were commonly in use.<ref name=T1T3.No_T2>1999 ad: On the left, in an aisle seat, a man who very much "filled" his airline seat while on the right side of the aisle is a height-challenged man whose shoe toes barely reach the floor {{cite magazine
|title=Is there a comfortable place between T1 and T3
|magazine=Digital Link
}}</ref><ref name=TxDefs.net/>