Major Japanese mobile phone carrier NTT Docomo Inc.'s nationwide service disruption last month hit over 12.9 million users, the company said in a report submitted to the communications ministry Wednesday.
The company said in the report that the system failure which began on Oct. 14 affected the voice communications of about 4.6 million people and data communications of about 8.3 million people. NTT Docomo had said at the time of the incident that a total of 2 million customers were left with no access to both voice and data services at one point. It revised that figure down to 1 million in its report.
The ministry, which believes the large-scale service disruption amounted to a "serious incident" under telecommunications business law, plans to decide administrative punishment on the unit of Nippon Telegraph and Telephone Corp. after carefully examining the report.
Eight NTT Docomo executives will voluntarily return part of their remuneration. President Motoyuki Ii will pay back 20% of his pay for a month. "We once again apologize" for the trouble, Senior Vice President Hiroshi Kobayashi told an online news conference.
In the service disruption, which occurred on the evening of Oct. 14, NTT Docomo customers could not register location information for two hours and 20 minutes, and the company's services were entirely unavailable for many of them.
The disruption was fully resolved around 10 p.m. on Oct. 15. The firm took 29 hours and six minutes to fully restore its services.
The issue stemmed from work to switch computer servers for devices using internet of things, or IoT, systems, including taxi fare payment terminals and vending machines. The problem was partially caused by workers failing to thoroughly follow the required procedures.
Confusion grew further as the firm informed customers that the service disruption had been fixed although connection difficulties were continuing, according to the report.
"I hope that the company will work hard to prevent a similar incident and that the entire industry will share the lessons" of the latest event, communications minister Yasushi Kaneko told a news conference Wednesday.
Among rival mobile carriers, SoftBank Corp. caused a major service disruption in December 2018, affecting some 30.6 million users.
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