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PRI Yellow Alarm
Yellow alarm or Remote Alarm Indicator (RAI) means that the system is receiving framing info,
but in this framing info the other side tells the system that it is not reading the system’s
transmitted framing info. Typically, this may be a broken connector in the TX part of the system
PRI cable. This could also indicate weak or noisy signal in the TX part of the system PRI cable.
PRI Blue Alarm
Blue alarm means that network on the far side of the CSU is unavailable.
Example:
The system is connected via a CSU (i.e. a Channel Services Unit’) as follows: System–
cableA–CSU–cableB–Network
If a CSU loses framing/sync from the network (example: a bad cable B), it shall no longer
send valid framing out on cable A towards the system. Instead it transmits "Blue Alarm".
Seen from a system receiving blue alarm, this means that the network on the far side of the
CSU is unavailable.