Panasonic KX-TD500 System Reference Manual page 1457

3.36 Digital trunk failure (RAI signal reception)
Error Code
Possible cause of
the malfunction
Countermeasures
Note
71xx xx=01 to 40 : Slot number
T-1/E-1 card (physical number xx) received the RAI (Remote Alarn indication)
signal sent from the Central Office.
Ask the T-1/E-1 carrier to check the line conditions. Or, check the equipment in
other switching system which your T-1/E-1 lines are connected with.
None
15-E-39