How did the outage happen during an upgrade?

It's been a week since an Optus outage left hundreds of customers unable to call triple 0 in an emergency.

But while there’s been widespread outrage in the days since, is anyone really holding the telco to account for the deadly error? 

Today, technology expert from Melbourne University Suelette Dreyfus on Optus's astonishing failure.

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Dr Suelette Dreyfus, Senior Lecturer at the University of Melbourne in the Department of Computing and Information Systems