O2 network outage ends: Here's what happened

O2's 3G and 4G data services restored as Ericsson blames an expired certificate for the mega-outage.

O2 has said the giant data network outage that left millions of customers unable to access the internet or other services from their phones has now ended.

The network operator said it restored its 3G data service by around 9.30pm last night, and said this morning that the 4G service has also started working again. Its data network had not been working since early yesterday morning.

"Our technical teams will continue to monitor service performance closely and we're starting the full review to understand what happened. We are really sorry for the issues yesterday," the company said.

O2 is the second largest mobile operator in the UK; the company says it has around 32 million connections to its network and also hosts virtual network operators, such as Sky Mobile and giffgaff, which were also affected by the outage. Other services that relied on the data network were also disrupted, including real-time information displays used on London's bus network.

O2 initially blamed the giant outage on a problem with software from a 'third-party' supplier, later confirmed to be Ericsson, which was also affecting other carriers around the world.

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Ericsson said the problem affected some nodes in the core network, resulting in network disturbances for customers in multiple countries using two specific software versions of the Serving GPRS Support Node - Mobility Management Entity product.

Ericsson president and CEO Börje Ekholm said the faulty software that has caused these issues is being decommissioned. The company said the initial root cause analysis indicates that the main issue was an expired certificate in the software versions installed with these customers. "A complete and comprehensive root cause analysis is still in progress," the company said.

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