Then we have to sent a bell boy (Mr.Siam) to knock the door instead of call to the room. // No complain about wake up call from guests.
ENG checked the systems and found the PABX card was error, they have to reset. The telephone system was back to normal at 21:37.
(ENG reported to me that that PABX card was effected from 10th Fl. to 25th Fl.)