T-Mobile US may have repaired network and restored voice and data services after an hours-long outage on June 15, but the Deutsche Telekom-owned operator will be more than aware that it will take somewhat longer to mend the reputational damage caused by the loss of service.

At least the operator appears to have identified the root of the problem, following erroneous reports of DDoS attacks that circulated on Twitter.

In a blog attributed to T-Mobile's president of technology, Neville Ray, the "trigger event is known to be a leased fiber circuit failure from a third party provider in the Southeast."

Redundancy measures built in to protect customers apparently failed, and "resulted in an overload situation that was then compounded by other factors. This overload resulted in an IP traffic storm that spread from the Southeast to create significant capacity issues across the IMS (IP multimedia Subsystem) core network that supports VoLTE calls".

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According to Ray, everything should now be back to normal, although the operator is still trying to work out what caused the initial overload failure.

It's clear the matter is far from over. The Federal Communications Commission (FCC), which not long ago approved T-Mobile's merger with rival Sprint despite widely held concerns, has already indicated it plans to investigate how and why the outage took place.

In a tweet, FCC chairman Ajit Pai described the network outage as "unacceptable", and said the FCC is launching an investigation. "We're demanding answers – and so are American consumers," Pai said.

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— Anne Morris, Contributing Editor, special to Light Reading