"While severe network disruptions affected all Portuguese operators during the blackout," mobile customers on Digi's network were significantly more likely to experience a complete loss of service," the study states.

According to the document, "up to 90% of Digi's subscribers were without mobile coverage for more than 24 hours. The outage exposed critical gaps in redundancy across multiple layers of infrastructure, from mobile sites at the edge to the core, potentially reflecting the limitations of this operator's less mature network build" in Portugal.

On the other hand, the MEO (Altice Portugal) network "demonstrated significantly greater resilience throughout Portugal during the blackout, demonstrating how robust and widely deployed battery backups can significantly mitigate and delay the impacts of power outages."

According to Ookla, "at the peak of the service interruption, between six and eight hours after the power loss, Meo subscribers were, on average, half as likely to lose service as NOS subscribers, four times less likely than Vodafone subscribers, and six times less likely than Digi subscribers."

In this sense, "tens of thousands of MEO subscribers likely remained connected for calls, messages, and data throughout April 28th." According to a study by Ookla, during the blackout on April 28th of this year, the Digi mobile network was the most impacted, while the MEO mobile network was the most resilient.