M1 has blamed its Feb 4 outage on an unexpected congestion problem and says it has taken steps to improve its mobile network.
The telco said the problem spread to different layers of its network, interrupting the process of confirming that people making calls on it were indeed M1 customers. This resulted in many customers being unable to make calls for more than five hours.
To prevent such an incident happening again, M1 has made changes to equipment that routes the signals involved for making call confirmations. It is also looking to enhance software to better manage sudden and unexpected congestion issues.
Last week's outage occurred despite intensive network tests the telco said it had carried out.
Upgrades on it begun more than two years ago to help the telco move calls to an Internet protocol platform - which uses Internet broadband lines to transmit voice data instead of circuit switchboards. This helps to reduce the number of dropped calls, helps customers make calls faster and improve call quality.
M1 said the upgrades will also allow functioning parts of the network to more quickly take over those that are facing problems.