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NBN to skip TCP/IP overprovisioning for 1Gbps plans

Other plans to receive up to 15% overhead to cater for higher layers of TCP/IP stack.
Written by Chris Duckett, Contributor

Users of Australia's government-owned national broadband wholesaler are set to receive up to 15% extra layer 2 capacity so that the tests the Australian Competition and Consumer Commission (ACCC) run at layer 7 can match the speeds claimed by internet service providers (ISPs).

In a test agreement [PDF] that appeared earlier this week, NBN described how it was going to allocate overhead for its new 100/20, 250/25, and 1000/50Mbps speed tiers.

The company has given its 500 to 1000Mbps plan the name of Home Ultrafast, 250/25Mbps is Home Superfast, and Home Fast is the label for 100/20Mbps. On copper-based fibre-to-the-node (FttN), fibre-to-the-basement (FttB), and fibre-to-the-curb (FttC) plans, NBN is going to use a range of between 25 to 100Mbps, and 5 to 20Mbps.

"For Home Fast and Home Superfast, NBN network management policers will provide an additional 15% overhead allowance to the AVC TC-4 downstream PIR at layer 2," the company said.

"This will allow end users to potentially achieve a downstream speed on their network approximate to numerical value of the published layer 2 wholesale downstream PIR where NBN infrastructure has capacity. Customers will need to consider this when configuring their networks."

The ACCC has previously said it wanted around 5% extra capacity to cater for TCP/IP headers.

However, for the fastest available plan, the test agreement states that 1Gbps plans will be restricted to 990Mbps due to "framing overhead".

"NBN Co intends to introduce an overhead allowance for the downstream component of most fixed-line wholesale speed tiers (with the exception of the Home Ultrafast up to 1000/50 and 1000/400 bundle discounts)," an NBN spokesperson told ZDNet in response to a question asking them to explain the difference between the overhead percentages.

"Where possible, NBN Co will provision this allowance into its wholesale speed tiers to accommodate protocol overhead, which includes the code used to ensure the correct delivery of data packets that otherwise impact a customer's broadband speed.

"NBN Co has chosen to not apply the additional bandwidth to our highest speed tier because it is already dimensioned to provide the highest possible speeds."

On an updated product roadmap released at the start of the month, NBN said it would introduce new bundle discounts for Home Fast, Home Superfast, and Home Ultrafast in May.

The roadmap also said this month the company would consult industry for an opt-in Residential Gateway Performance Program involving FttN/B modems and testing. Over the coming months, NBN intends to launch service health summaries across its copper-based technologies.

"Migration of the Weekly Line Speed reporting provided to RSPs for FTTN/B/C into a strategic framework. This is intended to enable RSPs to 'self serve' and obtain data either via B2B or manually," the roadmap states.

"This reporting framework is intended to be enhanced moving forward to provide key service health information available via the Service Health Summary and potentially expanded to other NBN technologies in future."

NBN is expecting next month to begin consultation on additional VDSL2 features that would reduce the number of resyncs due to "sudden large increases in noise".

Earlier this week, the company said it would limit the amount of maintenance it would do on its network as the company expects a surge in usage as higher numbers of people are staying home during work hours due to coronavirus-related social isolation.

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