T1 signals are transmitted using a scheme called Alternate Mark Inversion (AMI), where a ONE is represented by a pulse, and a ZERO is represented by no pulse. Pulses (which represent ones) always alternate in polarity, so that if, for example two positive pulses are received in succession, the receiver knows that one or more bits were either added or deleted from the original signal.

B8ZS coding is a scheme used in addition to AMI, which allows longer strings of consecutive zeroes to be transmitted, thus meeting the ones density requirement of T-1 standards which forbids consecutive strings of fifteen or more zeroes.