T-Mobile's 'significant capacity issues' led to network outage

Following an hours-long outage, T-Mobile repaired its network and restored voice and data services to its customers late Monday evening. But what went wrong?

A post on the company's website said that it was a capacity issue of some sort in the core of the network. "This is an IP traffic-related issue that has created significant capacity issues in the network core throughout the day," said a note attributed to T-Mobile CEO Mike Sievert. "Data services have been working throughout the day and customers have been using services like FaceTime, iMessage, Google Meet, Google Duo, Zoom, Skype and others to connect," he wrote.

Before Sievert's statement circulated on Twitter, one of the trending topics on Twitter was "DDoS attacks." Unfortunately, several media outlets and some random punters were erroneously reporting that several cellular networks in the US were all having outages at the same time, so we must be under attack. (We weren't.)

The folks at Nokia Deepfield team, when asked by Light Reading, surveyed their major carrier network customers and wrote that "there was nothing happening in the large wireline networks today, and nothing extraordinary was recorded anywhere." On Twitter, Cloudflare's CEO was also actively debunking the erroneous DDoS attack narrative.

That leaves us with what went wrong at T-Mobile. We don't know yet – and T-Mobile hasn't responded to a request for a news interview. A former Verizon lawyer who now has a government job posted that the FCC is opening an investigation into the six-plus hour outage, so there will at least be some publicly available, technically worded excuses coming soon.

Phil Harvey, Editor-in-Chief, Light Reading

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