NTT Docomo communications outage resolved after about 14 hours; cause was “switch congestion,” with no signs of unauthorized access - ITmedia NEWS

　NTT Docomo announced on November 6 that the outage affecting mobile phone services for “5G SA (Standalone)” subscribers, which had continued nationwide since around 11:18 a.m. on November 5, was restored at around 1:20 a.m. on November 6. Affected users had difficulty using voice calls, data communications, and SMS for approximately 14 hours.

　The cause was congestion at a switch accommodating “5G SA” subscribers. 5G SA is an option that communicates using only dedicated 5G equipment and is promoted as a service that enables smooth communications even when 4G communications are congested.

　Docomo stated that, based on its investigation to date, including before and after the outage, it had not identified any signs of unauthorized access or events indicating a cyberattack.

　Users other than 5G SA subscribers and MVNOs using Docomo lines were unaffected. Emergency calls were also unaffected.

　The response measures have been completed, but Docomo advises users who are having difficulty using the service to try restarting their mobile phones or turning airplane mode on and off. Users who changed their network settings to 4G as an interim measure are being asked to restore the settings.