Yesterday, Neville Ray, President of Technology at T-Mobile, shared more information about the cause of T-Mobile’s outage on Monday:
Many of our customers experienced a voice and text issue yesterday, specifically with VoLTE (Voice over LTE) calling…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.
We have worked with our IMS (IP Multimedia Subsystem) and IP vendors to add permanent additional safeguards to prevent this from happening again and we’re continuing to work on determining the cause of the initial overload failure.
So, I want to personally apologize for any inconvenience that we created yesterday and thank you for your patience as we worked through the situation toward resolution.