PURPOSE: To perform normal communication even if a fault state is generated owing to the transmission delay of a trunk line, by preventing an increase in the traffic of the trunk line from being caused, by inhibiting a signal characteristic to a polling system from being sent to the trunk circuit.
CONSTITUTION: A polling scheduling circuit 1 schedules polling for subordinate terminals TD1∼TDn. For a schedule for the polling for the subordinate terminals TD1∼TDn in the order of their suffixes, a scheduling table which stores polling signals for the subordinate terminals TD1∼TDn successively is provided. When the circuit 1 reads the polling signal for the terminal TD1, a polling indication is supplied to a polling-indication-signal generating circuit 2 together with the polling signal. This circuit 2 generates a polling indication signal, which is sent to a trunk line L1 via a transmitting circuit 3 together with the polling signal.
ISHIDA NOBUYUKI
HIROGAMI MAKOTO
HARA TOKIHIDE
WAKAYAMA IKUO
TOKI RIYUUICHI
NIPPON TELEGRAPH & TELEPHONE
OKI ELECTRIC IND CO LTD
NIPPON ELECTRIC CO
HITACHI LTD