In 2015, NBN Co will begin moving into the so-called multi-technology mix rollout of the National Broadband Network (NBN) that will see the company abandon much of the fibre rollout in favour of fibre to the node and hybrid fibre-coaxial (HFC). It is still unclear, however, what premises will get what technology.

(Image: Screenshot by Josh Taylor/ZDNet)

Last year, Communications Minister Malcolm Turnbull directed NBN Co to use the most cost-effective technologies to deliver a minimum of 25Mbps to every premises by 2020. This will mean that a large portion of premises that had been slated to get fibre to the premises under the former Labor government will now instead get the NBN via fibre to the node, fibre to the basement, or hybrid fibre-coaxial.

Which areas will get what technology has yet to be announced by NBN Co, and CEO Bill Morrow has said that the company will determine, area by area, which technology is most suitable.

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"When it comes to the technology that is going to be used for a neighbourhood, it is not that simple; you can't call it out now and do rough estimates," he said in 2014.

"We might say this area is for fibre to the node, but until you actually get out there and do the survey properly to see what kind of condition [the copper] is in, you're not going to be sure.

"The fact is, we're going to give you a technology that gives you what that minimum service level is. We commit to that, we're going to do it as soon as we can, and we're going to let you know as soon as feasibly possible."

Some light has been shed on the planning process that NBN Co is now developing, with an internal slide released by NBN Co under Freedom of Information this week (PDF). The slide shows that the planning process around the multi-technology mix model is broken up into five steps.

Firstly, NBN Co will scope out the exact area the next stage of the rollout is covering using the geospatial data that NBN Co has obtained to plan the rollout.

Next, NBN Co will look at each of the potential technology choices for that area, the cost for each technology in that area, and estimated revenues and net present value for that area.

NBN Co will then choose the technology that maximises net present value and "propose a practical rollout profile and suggested sequence to maximise cash flows within a set of agreed constraints".

This indicates that a specific area is likely to get one technology based on what is the best value for the area. For example, it is unlikely that in an HFC area, NBN Co would use both HFC and fibre-to-the-node services.

NBN Co will then calculate the costs and financial metrics based on the timing of costs and revenues in that area, and validate the rollout against peak funding requirements.

The company will then create data to explain to the public and NBN Co's stakeholders why a technology was chosen for that area.

The slide is the first glimpse into NBN Co's new rollout methodology, which is expected to kick into gear later this year following further trials of fibre to the node and HFC, and the regulatory approval of the amended agreements with Telstra and Optus.

ZDNet sought further comment from NBN Co, but had not received a response at the time of writing.