The retiring head of the company charged with building and operating the National Broadband Network has rejected suggestions he was forced out by the company's chairman.

NBN Co chief executive officer Mike Quigley says he is retiring from corporate life after four years leading the rollout of the network.

When asked by The World Today's Peter Ryan about speculation he was being forced out, Mr Quigley did not give a direct answer.

But he later said his decision to leave did not come as a result of discussions with NBN Co chairman Siobhan McKenna.

Mr Quigley said he has a very good relationship with Ms McKenna.

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"It's four years next week since I've been in this role, and it's a pretty tough role... we also announced in the last week or two our results from our revised forecast and we hit all those forecasts, so now is the right time to hand on to someone else," he said.

NBN plans compared Fixed line speeds 100mbps (1000mbps in future) 25-100mbps Satellite speeds 12mpbs-25mbps 12mpbs-25mbps Fibre to home 93% of premises 22% of premises Fibre to node 0% of premises 71% of premises Finished by 2021 2019 Cost $44 billion $29.5 billion Read our explainer on the network differences

Mr Quigley will continue to serve as CEO until the board appoints his replacement.

Opposition communications spokesman Malcolm Turnbull has been highly critical of Mr Quigley's performance, and believes he has been pushed.

"We know the [NBN Co] chairman Siobhan McKenna has been trying to sack him for some time, and he's been protected by Stephen Conroy, she's had headhunters out to find replacements, so finally he's left," Mr Turnbull said.

Earlier Ms McKenna paid tribute to Mr Quigley's work.

"NBN Co has been fortunate to have Mike as chief executive over the past four years. His intellect, tenacity and knowledge of telecommunications products and network architecture have taken NBN Co from a policy vision to a successful operating entity," she said.

"The directors are proud of Mike's achievements."

NBN rollout hit by controversies over delays, asbestos scares

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The NBN has been dogged by a series of problems, including rollout delays, and, most recently, an asbestos scandal.

Mr Quigley has acknowledged mistakes have been made.

Sorry, this video has expired Turnbull says Quigley pushed from NBN post

"In a project of this magnitude you're constantly having to make judgements and make calls, and you invariably make mistakes along the way, but what I'm pleased about is we've made the right decisions in some of the big decisions," he said.

"I think that criticism, we have to take on board, and we have to keep questioning ourselves. And I think that’s why I think the scrutiny that we do see from our critics is something that's important."

Mr Quigley came out of retirement to become NBN Co's founding chief executive.

"My job was to lay the foundations for the NBN for the next 30 years. That job is largely complete," he said.

"The role of the next CEO will be to build on these foundations.

"The ramp-up in construction and the news last week that the company had passed more than 200,000 premises with fibre gives me further confidence that the NBN build can be delivered by 2021 in line with the projections in the company’s corporate plan."

Albanese, Wong issue their thanks

The Federal Government has thanked Mr Quigley for his role in establishing NBN Co.

Communications Minister Anthony Albanese and Finance Minister Penny Wong released a joint statement saying Mr Quigley was "eager to join the project because he understood the importance of nation-building infrastructure that is essential for our nation's economic future".

"Mr Quigley can be tremendously proud of what he has achieved."

Sorry, this video has expired Albanese praises outgoing NBN Co chief

Mr Turnbull says he does not think a replacement should be appointed before the election.

"I would be amazed if the board appointed a new chief executive six, eight, nine weeks out from an election," he said.

"That would be an act of hubris and recklessness, that, I would be astonished if they were going to do that."

Potential asbestos exposure linked to the network is being investigated across the country.

Telstra has taken responsibility for potential exposure at several sites.

But Comcare's Paul O'Connor told Senate estimates earlier this year that he believed the asbestos problems are the result of a breakdown in the NBN’s contract and management chain.