Prank call rejection system for home country direct service

This paper describes a prank call rejection system, which rejects prank calls to KDD Japan Direct/sup SM/, a home country direct service. The system issues an announcement in Japanese which instructs KDD Japan Direct/sup SM/ customers to speak a key-word in Japanese. If the system recognizes the key-word, then it switches the line to a telephone operator. If not, the call is assumed to be a prank call and the line is cut off. We developed a prototype prank call rejection system and evaluated it over several months in phases. Results showed that over 93% of prank calls were rejected while only 2% of customer calls were rejected. The figure for rejected calls includes cases in which customers did not speak the key-word. Almost all customers rejected in the first call, however, tried to place a call again and successfully spoke the correct key-word. The commercial system was developed and has been in operation at the KDD International Switching Center since March 1996.