NTT DoCoMo Inc. and NTT Communications Corp. said Wednesday the problems with DoCoMo's international roaming services in mid-August were caused by structural defects in a networking system.
The companies said the international communications network for DoCoMo's overseas calls, provided by NTT Communications, could not evenly channel information such as callers' geographical locations to resources and had to rely on limited paths. The problem surfaced because call traffic from abroad increased during the summer vacation season.
The firms said they will soon submit a final report on the cause of the trouble and planned countermeasures to the Internal Affairs and Communications Ministry.
NTT Communications said programming remedies have already been made, while it will enhance the system's ability to deal with increased traffic volume.