Telstra has taken responsibility for more than 1,400 calls to triple zero that went unanswered earlier this year after a series of infrastructure and network failures led to a national outage.
An investigation, conducted by the Australian Communications and Media Authority (ACMA), found 1,433 calls were not connected to an operator on May 4.
The ACMA labelled the outage, attributed to a damaged cable in regional NSW, as the most serious disruption to Australia's triple-zero service since it was introduced.
"It's a very serious disruption," ACMA chair Nerida O'Loughlin said.
"Telstra worked very hard on the day to make sure that they got in touch with people who were trying to call through, but really, this has highlighted the need for Telstra to significantly improve redundancy in its network.
"We have agreed a court enforceable undertaking to ensure that Telstra continues to implement those changes to their system, which will make sure that these disruptions don't happen again."
The ACMA's report revealed almost 4,000 calls were initially affected, and while more than half of these were terminated, 1,433 could not be connected.
Hundreds of traffic lights in Victoria were also affected, and there were reports of disruptions to other telephone services and EFTPOS machines.
The investigations found a Victorian exchange experienced a partial transmission failure, which was followed by a fire outside a Telstra pit near Orange and then a software fault.
Telstra committed to improving the network by developing new protocols and using international best practice as a benchmark.
Communications Minister senator Mitch Fifield said the investigation's findings would help improve the network.
"The Government takes the safety of Australians seriously and the triple-zero service is vital in keeping our community safe," he said.
"With the measures the Government [is] putting in place, Australians can feel confident the service will have greater safeguards in times of need."
Telstra accepts responsibility for call failures
Telstra's executive of regulatory affairs, Jane van Beelen, said the outage was "complex and unprecedented" and that the telco took responsibility for the outage.
"We take our responsibility as the service provider for triple zero extremely seriously," Ms van Beelen said.
"One failed call to triple zero is one too many and we apologise for what occurred."
Ms van Beelen said Telstra conducted its own investigation and concurred with the findings presented by the ACMA.
The damage was initially believed to be caused by a lightning strike, ABC reported at the time, but investigators from NSW Rural Fire Service ruled it out.
The ACMA chair said they were "satisfied with what Telstra has done to date" and determined people were not seriously impacted by the outage.
"The investigation determined that there did not seem to be any adverse implications of the failure for people who may have been in trouble at the time," Ms O'Loughlin said.
However, during the national outage, a Redfern woman whose husband was caught in an electrical fire, reportedly jumped into a car and drove to their nearest fire station when their triple zero call went unanswered.
The husband, Apollo Karanges, reportedly suffered burns to 40 per cent of his body when he attempted to put out an electric blanket that caught fire, after emergency services did not connect.
Telstra announced they would implement further redundancy measures including improved monitoring and fault detection as well as infrastructure and software upgrades.
Ms van Beelen said they would work with emergency service operators on developing crisis plans and protocols to prepare for future outages.
