Telstra has blamed a software fault for its second widespread network outage in a month, which left customers unable to make calls or use mobile data.
The telecommunications giant said a software fault triggered multiple elements across its 4G network to fail, and a further fault caused an interruption on its back-up hardware, which resulted in customers dropping back to the 3G network.
There was then a significant disruption to 3G voice and data services as the network became flooded with data traffic.
Telstra is yet to disclose how many customers were affected by Monday's outage but said it took about two hours to restore full service.
A map produced by fault tracking site Aussie Outages on Monday showed the problem affected a number of hubs around the country, including in Sydney, Hobart, Brisbane, Melbourne, Perth and Adelaide.
The company said it is still investigating the root cause of the software fault and is working closely with technology vendors on the specific element of software which triggered the issue.
"Our teams have worked around the clock to restore services and to investigate why the redundancy in our network did not prevent customer impact, for which we are deeply sorry," Telstra said on Tuesday.
"We will continue to closely monitor network stability and performance."
Telstra group managing director networks, Mike Wright, on Monday apologised to customers, but denied the disruption had anything to do with outrage problems earlier in the month where customers were unable to make or receive calls following issues with the 4G network.
Earlier in May, Telstra customers were affected by issues with the company's 4G network caused by technical changes made ahead of upgrades to equipment in Melbourne.
A couple of days later, triple-0 voice calls were affected across three states after a Telstra cable running between the regional centre of Orange and Bowral in southern NSW was damaged by what appeared to have been a lightning strike.
The issue resulted in problems with calls to the police, ambulance and fire brigade numbers in NSW, Victoria, Western Australia, South Australia and Tasmania.
Telstra shares are at a seven year low, and were trading 2.9 per cent lower at $2.72 by midday on Tuesday.
