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yellow alarm

One of the three alarms to indicate problems with T1 transmissions. A yellow alarm signal is sent back toward the source of a failed transmit circuit in a T1 transmission path. A yellow sends zeros in bit two of all timeslots. See also AIS, blue alarm, red alarm.

ZCS

Zero Code Suppression; the insertion of a one bit to prevent the transmission of eight or more consecutive zero bits. Used primarily with T1 facilities, which require a minimum ones density. See also ones density.