What are the red, blue, and yellow alarms in a T1 system?

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A7. The three different alarms are used to indicate different problems in transmission or reception of data in the T1 system. To explain the different alarms, it is necessary to have a simple T1 system model that has a T1 signal sourced from the central office (CO) through a repeater to the customer premises equipment (CPE) and back. The red alarm is actually a CPE state resulting from the detection of an incoming signal failure (i.e., from a line break). The yellow alarm is transmitted to indicate the loss of an incoming signal. In the case where the CPE is in the red alarm state, it will transmit the yellow alarm to the repeater. The blue alarm is transmitted upon loss of the originating signal or when a signal is actively disrupted. In the case where the repeater receives the yellow alarm, it will transmit the blue alarm back to the CO. Upon receiving a blue alarm, the CO will transmit a yellow alarm to the repeater to indicate the loss of incoming signal. It may seem confusing as ... more
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