The Federal Communications Commission (FCC) has revealed that 92 million calls were blocked during AT&T's network outage in February.
According to the FCC's report into the incident, the outage also prevented 25,000 people from contacting emergency services.
The outage began around 3:30am Eastern on 22 February and brought down a significant number of AT&T customers.
The FCC notes that the outage lasted at least 12 hours before AT&T was able to restore services.
A couple of days after the outage, the carrier said the outage occurred after it implemented a network change with an equipment configuration error.
“When you sign up for wireless service, you expect it will be available when you need it – especially for emergencies,” said FCC Chairwoman Jessica Rosenworcel.
“This ‘sunny day’ outage prevented consumers across the country from communicating, including by blocking 911 calls, and stopped public safety personnel from using FirstNet. We take this incident seriously and are working to provide accountability for this lapse in service and prevent similar outages in the future.”
Users were impacted in all 50 US states plus Washington, D.C., Puerto Rico, and the US Virgin Islands, with all voice and 5G data services for AT&T wireless customers unavailable, affecting more than 125 million devices.
This led to more than 92 million voice calls being blocked and more than 25,000 calls to 911 call centers failing.
The FCC's report also found that the outage cut off service to devices operated by public safety users of the First Responder Network Authority (FirstNet).
"AT&T prioritized the restoration of FirstNet before other services but did not notify FirstNet customers of the outage until three hours after it began, and nearly one hour after service was restored," said the FCC.
Following the release of its report, the FCC said the Public Safety and Homeland Security Bureau has referred this matter to the Enforcement Bureau for potential violations of FCC rules.
The regulator stated that AT&T failed to carry out adequate lab testing around the configuration changes and "did not identify the potential impact to the network of that or similar misconfigurations."
Following the outage, the FCC said that AT&T had taken numerous steps to prevent a reoccurrence, and has engaged in ongoing work to ensure network robustness and resilience.
"Within 48 hours of the outage, AT&T implemented additional technical controls in its network. This included scanning the network for any network elements lacking the controls that would have prevented the outage, and promptly putting those controls in place."
