NBN Co urged to over-provision downlink on all services

NBN Co is facing renewed pressure to over-dimension all its broadband services to make them capable of reaching the topline speeds that they promise.

The Australian Competition and Consumer Commission (ACCC) put its weight behind over-dimensioning this morning; Telstra has made similar overtures directly to NBN Co.

The ACCC’s concern stems from the latest broadband speed monitoring report, which highlights the “percentage of maximum plan speed used by protocol overhead” for the first time.

The report has a habit of raising one new issue or insight every time it is published; the last time it was a new metric that shamed retail service providers (RSPs) whose services underperformed advertised speeds.

Now, the ACCC seems keen to offset the effect of the protocol overhead - the amount of bandwidth used up in carrying data packets and ensuring they reach their intended destination.

Even the earliest retail service providers (RSPs) to connect customers to the NBN noticed the maximum achievable speed on a 100Mbps plan was around 95Mbps, owing to overhead.

However, it is only recently in NBN Co’s wholesale pricing review that the network builder has offered to offset the impact of overhead on some plans by over-provisioning them.

Currently, NBN Co is planning to do this for a new range of asymmetrical higher-end plans - its proposed 100/20Mbps and 250/25Mbps products.

The company said last month that it intended to “over-dimension the downstream speed of both” products to allow for protocol overhead.

In the case of 100/20Mbps, NBN Co has indicated it will actually provision the product as 110/20Mbps, thus giving users the prospect of hitting 100Mbps on a plan marketed as 100Mbps.

It’s not clear how much the 250Mbps service would be over-provisioned to perform similarly.

What is clear, however, is that there's an appetite for this thinking to be applied to all NBN services, not just a selected few.

“NBN Co should apply the proposed ‘over-dimensioning’ approach (to account for end user speed impacts due to protocol overheads) consistently across all speed tiers,” Telstra said in a submission to NBN Co’s pricing review.

It appears the ACCC is ready to back this, noting its broadband speed measurement report “shows that consumers can never make full use of their plan speed even outside busy hours, with NBN speed tests never exceeding much more than 95 percent of the plan speed.”

“This is the case for all NBN speed tiers,” the ACCC’s report states. [pdf]

“This is because headers, or tags, are added to consumers’ communications when they are sent over a network, to ensure the communications are sent to the right network addresses.

“The current capacity does not appear to allow for this extra data, preventing the communications from being sent at the maximum plan speed.

“NBN Co could resolve this if it allowed services to run five percent faster before enforcing speed limits.”

The ACCC report noted that overhead typically accounted for between 4.5 percent and 4.9 percent of bandwidth.

Within each NBN speed tier, the highest observed speed for any whitebox [device used to measure speeds] was 95.5 percent,” the report stated.

“This suggests that around four percent to five percent of maximum plan speed is used up by protocol overhead.”

An NBN Co spokesperson indicated the company is open to over-provisioning the downlink on more - but not all - plans.

"It’s important to note that NBN Co operates as a wholesale layer 2 service provider – and the protocol overhead, which causes the degradation to the download speeds received by customers, occurs at the layer 3 retail service," the spokesperson said.

"Based on the industry’s interest in this feature, NBN Co is considering expanding its proposed scope of works to over-dimension the downstream speed of the 50/20, 100/20, 110/40 and 250/25 product tiers.

"NBN continues to consult with RSPs and is working through the technical aspects required to sufficiently over-dimension key product tiers to compensate for protocol overhead so that more customers may receive faster download speeds.

"The company will announce the final outcomes of its four-month consultation process towards the end of this month."