Major outage at operator with millions of subscribers: Cause of the problem under investigation

NTT Docomo, Japan's largest mobile operator, reported nationwide outages affecting voice calls, mobile data and SMS services, with the disruption also hitting other carriers that rely on its network infrastructure. The company said it is still investigating the cause of the failure, which struck a subscriber base of tens of millions. The incident matters because Docomo's network underpins wholesale access for rival operators, so a single fault can cascade across Japan's telecom market. Investors will watch for Docomo's root-cause disclosure and any regulatory response from Japan's communications ministry over network resilience.