Japanese MNO KDDI’s network went down at the weekend, reportedly leaving around 40 million people unable to connect.

KDDI’s mobile network went down very early on Saturday morning and carried on over the weekend, according to a series of updates on its site. The outage seems pretty widespread and according to various reports up to 40 million people may have been left without service.

In the early hours of Saturday morning the operator tweeted: “From 01:35 today, it is difficult to use our communication service. We are currently working on recovery work, but we have updated the information on the causes / effects that are known at this time. We deeply apologize for any inconvenience caused to our customers.”

The advice as the operator tried to the get the network back up and running was to use landlines and if you don’t have one (as is increasingly the case as people rely on their mobiles more), to use a payphone: “Since it is difficult to use emergency numbers, please use landlines or public phones. Due to communication problems, the KDDI Customer Centre and other inquiries are currently very crowded. We apologize for the inconvenience, and thank you for your patience.”

By this morning it seemed to be getting back to normal with regards to data, though voice calling was still experiencing issues, with another statement explaining: ‘Data communication is generally recovering nationwide. In addition, due to measures such as flow control, it is still difficult to use voice calls. We deeply apologize for any inconvenience caused to our customers.’

In terms of the cause of the outage, KDDI said ‘Traffic congestion has occurred in the VoLTE switchboard due to a facility failure before dawn on Saturday.’ The Japanese power grid has been under huge strain apparently, thanks to the a significant heatwave in recent days. Its hard to say whether these two items are related but it seems plausible.

In November last year it was reported fellow Japanese operator NTT suffered a system failure which left 13 million disconnected. Apparently, that took about 29 hours to resolve and was described as a ‘serious incident’ by the communications ministry.

Network outages happen of course but they don’t usually last as long as a weekend, which if you don’t happen to find yourself with a landline or near a phone box could prove hugely disrupting. And more than that if you need to get hold of someone in an emergency situation.

Perhaps in response to what seems to be a larger that usual outage, the KDDI share price took a modest hit, but appears to be back on the up as Monday progresses.

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