i using the system version is R6.2 and with IAA function. one E1 ISDN trunk (without DID).
some extenal phone number can't dail into a station.(at extenal,the calling call the station through the IAA ,will hear the busy tone)
see bellow:
calling(A)---------IAA(PBX)----------------called(B)
the calling call called can hear the busy tone .
anybody can give me a management.

