FCC Public Safety and Homeland Security Bureau Seeks Comment on Effects of June 15, 2020 T-Mobile Outage on Public Safety Entities, Government Entities, and Consumers
From T-Mobile's statement:
"The trigger event is known to be a leased fiber circuit failure from a third party provider in the Southeast. This is something that happens on every mobile network, so we�ve worked with our vendors to build redundancy and resiliency to make sure that these types of circuit failures don�t affect customers. This redundancy failed us 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."
Other notable national telecommunication failures
AT&T - January 15 1990, AT&T Long Distance Network Collapse
MCI Worldcom - August 1999, Multi-day frame-relay network failure
Centurylink - December 27, 2018, 37-hour nationwide outage