A quarter of FttN customers on NBN 100 and NBN 50 plans are not receiving the speeds they pay for. Credit:Graham Denholm

Belong is the latest Australian telco to stop selling 100Mbps NBN plans to homes connected via Fibre to the Node or Basement, as those technologies are struggling to keep pace due to their heavy reliance on old infrastructure.

With the bulk of the NBN rollout due to be completed by July, around 40 per cent of Australian premises will connect to the nationwide broadband network via Fibre to the Node (FttN or Basement (FttB). FttN relies on the copper phone lines to cover the last few hundred metres to homes, while FttB runs fibre into the basement of large buildings and then relies on the building's internal copper wiring to reach each dwelling.

"A number of our customers on FttN and FttB do not have connections that are capable of achieving 100Mbps," said a Belong spokesperson.

"It is often the case that customers that sign up to these plans will be subsequently notified that they cannot achieve top speed and end up downgrading to a lower plan or leaving."