NBN Co has revealed a quarter of its fixed wireless cells - about 1730 - nationwide are capable of wholesale speeds of less than 12Mbps during the “busy hour”.

The network builder provided for the first time a more detailed breakdown of what its fixed wireless network is capable of.

It said that 46.08 percent of cells “averaged wholesale access speeds during the busy hour … above 25Mbps”.

A further 29.16 percent of fixed wireless cells were capable of average wholesale access speeds of between 12Mbps and 25Mbps in the “busy hour”, while 18.39 percent were capable of access speeds between 6Mbps and 12Mbps.

The proportion of cells that only achieve 6Mbps or less in the “busy hour” has previously been disclosed.

NBN Co has come under criticism in recent months for the performance of its fixed wireless network.

The network builder only defines a cell as congested once users connected to it average 6Mbps or below during the peak hour.

Due to long lead times in upgrading cells, some will see average speeds dip below 3Mbps, at which point the congestion is officially classified as “unacceptable”.

NBN Co cautioned about reading too much into the new set of numbers.

“This data does not reflect actual speeds experienced by end users,” it said.

“Actual speeds experienced at any point in time are determined by a range of factors including the speed tier purchased, available CVC, number of simultaneous users, and the bandwidth provisioned within the networks of retail service providers.”

But numbers released separately by retail service providers appear to show that actual performance is considerably below the wholesale average.

In March, Telstra revealed around half of NBN fixed wireless users on 12Mbps and 25Mbps plans saw 40 percent or less of the speeds they paid for in the evening peak.

Aussie Broadband similarly had 1600 of its fixed wireless customers submit a total of 29,000 speed tests, and found that 25Mbps and 50Mbps users “averaged less than half their ordered speed for half the day”.

“The only time they were likely to experience close to full speeds was somewhere between 2am and 5am,” Aussie Broadband - a company that has fast built a reputation on low contention ratios - said.

As retail confidence in NBN Co’s fixed wireless broadband product has dipped, many retailers are staying clear of offering the highest-tier 50Mbps plan, which was launched back in December 2015.

Telstra, for example, still does not offer a 50Mbps service, maxing its fixed wireless offerings out at 25Mbps.

NBN Co said that the “average busy hour speed across all cells on the fixed wireless network over the month of February was 25Mbps”.

Given all major RSPs have been stung for selling NBN fixed-line connections that were incapable of hitting maximum retail plan speeds, it appears likely they are holding off on offering 50Mbps fixed wireless plans to avoid a repeat of that situation.

The new release of NBN fixed wireless numbers is also likely to fuel calls to standardise the metrics used to define congestion on this part of the NBN.

Aussie Broadband has been particularly vocal on the mix of definitions in the market.

The ACCC currently asks RSPs to define congested periods as the evening peak - between 7pm to 11pm - whereas NBN Co mostly talks about congestion only in the “busy hour”.

Properly defining what congestion looks like on the fixed wireless network could give users better clarity on what sort of performance they should expect.

“On an operational level, we are regularly told by NBN Co that a 25Mbps service that regularly slows down to 13Mbps is acceptable,” Aussie Broadband said.

“Our concern is that none of the thresholds - even the highest one at 13Mbps - would be acceptable to customers.”