Fibre-to-the-node connections are acting as a drag on overall speed averages on the NBN, prompting calls for action to remediate problems or migrate more users onto cheaper plans.

In a surprising move - given how politically-charged debates around access technologies can be - the latest competition watchdog-commissioned broadband speed test report [pdf] breaks out data by access technology for the first time.

The move appears aimed at spurring action on consistent “underperformance” among NBN connections, which the Australian Competition and Consumer Commission (ACCC) has called out in each of its speed reports.

Critically, though, the move narrows the blame on the part of the NBN that is responsible for most underperforming connections.

The ACCC’s speed report classes a service as underperforming “if no more than five percent of the speed tests that we conducted over the service achieved a speed that was above 75 percent of the maximum plan speed.”

The commission said 13.2 percent of all speed test boxes are connected to underperforming services - the first time it has disclosed this figure.

The ACCC said today that “most” of the underperforming services are in the fibre-to-the-node footprint.

“Underperforming services, which represent about 13 percent of all tested connections and are mostly fibre to the node (FTTN), continued to significantly impact the overall download speed results,” it said.

“These services never come close to delivering the maximum speed promised, because of either limitations with some FTTN lines, or connection issues such as in-house wiring faults.”

ACCC chairman Rod Sims encouraged customers of underperforming services “to contact their internet service provider to ask whether the problem can be fixed or about moving onto a cheaper plan.”

The ACCC numbers show that fibre-to-the-premises (FTTP) and HFC customers, on average, see around 88 percent of maximum plan download speeds and 92 percent of upload speeds.

FTTN users, by contrast, see 79.6 percent of download speeds and 77.3 percent of upload speeds, on average.

It isn't clear what prompted the ACCC, nor its contracted speed test service provider, to suddenly start breaking out problems by access technology.

Certainly, the timing is curious in the lead-up to a federal election at which NBN is already being touted as a policy issue.

Federal Labor raised the possibility of an NBN writedown this week, a prospect that has been flatly rejected by the current government. Labor has also been under pressure to fix parts of the NBN, or at least deploy better access technology for the remainder, if it comes to power at the next election.

Problems in the FTTN portion of the network have long been documented.

At the end of last year, it was revealed that 1.3 percent of FTTN premises - at least 15,000 in real terms - would never reach the government’s minimum 25Mbps peak speed promise, and therefore need to be flipped to a different connection type.

It's also previously been revealed that up to 75 percent of FTTN users paying for 50Mbps or 100Mbps retail services won't ever see that “absolute” topline speed, though NBN Co claims they may get near enough to the mark not to care.

The latest ACCC report also shows the impact of peak period speed cuts made recently by the TPG group of companies.

However, in good news for TPG, customers in the ACCC’s sample saw only a minor impact from this.