Wednesday, 06 December 2017 05:01

HFC network will need work to be fit for NBN: experts Featured


Technical experts who have closely followed the rollout of the NBN say Telstra's HFC network will need considerable work done on it to meet the needs of NBN customers.

Last week, NBN Co, the company rolling out the national broadband network, said that network issues would mean a delay in HFC connections of anything from six to nine months.

Dermot Cox, an HFC expert and business consultant, told iTWire the HFC platform was fine, but "running out of capacity, yes. In need of field workforce training, yes; in need of robust NBN Co workforce craft practices, yes".

"My observation is that NBN Co's engineering needs time to catch up, increase the bandwidth from 750MHz to 862MHz, finalise plans to deploy new cable modems and turn on DOCSIS 3.1 early in 2018," he said.

"They need to update some HFC amplifiers and do node splits (reduce the customers in a node-serving area) in those areas of hot demand: again, normal everyday events for a network operator, but for NBN Co they have to move much faster than Telstra ever did…"

Cox said because massive new connections had been connected recently, NBN Co had to use the bottom end of the bandwidth spectrum. "...this low end spectrum is susceptible to ‘noise', and so caused some cable modems to reset. This is no different to other broadband technologies."

He said that as far as he was concerned, the key insight in NBN Co's announcement was the reference to customer experience. "Anecdotally, it hasn’t been as smooth as say how Foxtel or Telstra delivered new Pay TV or cable broadband services to its customers via their construction partners; across the same platform," he explained.

Damien Ivereigh, chief executive of Tasmanian ISP Launtel, said his understanding was that there were multiple issues. "Some are physical connectivity (poor cables, bad joints etc). However, the biggest issue seems to be that the bandwidth that has been allocated to NBN Co to avoid the existing Telstra Foxtel services has turned out to be less capable than expected. The HFC is a bit like the copper PSTN services there is a 'co-existence' period where the NBN has to 'share' the bandwidth with Foxtel until the Foxtel services are turned off.

"Whether they already have some technical solution to this problem or it's a 'go back to the drawing board' moment to come up with one, I am unclear. Given that the issue seem to be a transition one, rather than a long-term one, I have no reason to believe that NBN Co will end up scrapping (use of) the HFC altogether. Indeed, there are enormous political pressures on NBN Co and the government not to scrap it. (Prime Minister) Malcolm Turnbull extolled the virtues of using the HFC network on numerous occasions."

As iTWire reported on Tuesday, Turnbull was the one who championed the idea of using cable to get the NBN project completed faster.

Mark Gregory, an associate professor in the School of Engineering at RMIT University, said the problem had arisen because there was a mismatch between older equipment in the HFC network and the new ARRIS equipment.

"NBN Co has rushed to add customers before completing the upgrade to the new equipment and adding DOCSIS 3.1, hence many of the issues. The Telstra network should be able to be used when the upgrade is completed, not before," he said.

"The Telstra Foxtel cable network was built to have about a 30% connection rate in the suburbs where it was rolled out. The cable was not connected to multi-dwelling unit buildings (apartments) and some streets and cul-de-sacs were bypassed. The Telstra/Foxtel HFC deal means that Foxtel retains access to the HFC and this limits the frequency bands available for NBN traffic."

Gregory was of the opinion that the HFC network should have had remediation work carried out prior to being used to connect consumers to the NBN. "The NBN is anticipated to have about 70% to 80% connection rate in a suburb, which requires the HFC network to be rebuilt with more fibre, nodes and coaxial cables," he pointed out.

"To provide the capacity needed for this connection rate, the upgrade to DOCSIS 3.1 is required and the equipment for this upgrade is not expected to become available to NBN Co until Q2 2018."

He said the figures provided by NBN Co were "designed to be difficult to understand", and it was "the ongoing secrecy and lack of transparency that should be of concern to consumers".

While the NBN Co chief executive Bill Morrow has pledged that the six-to-nine-month HFC delay would not have an impact on the 2020 deadline for completion of the network, Gregory said this was unlikely.

"The overall effect of the delay is to push back the earnings from HFC connections and potentially cause NBN Co to miss the 2020 deadline for completion," he said.

"It is highly unlikely that the NBN will be completed in 2020. NBN Co has previously reported the cost for remediation work and the DOCSIS 3.1 upgrade so the key outcome of the delay is that NBN Co's revenue forecasts for 2018 to 2021 are now inaccurate as the HFC connection revenue will be frozen at its current level until new connections occur in Q2 2018," he said.

Gregory, who has been a critic of the multi-technology technology mix which was introduced by the Coalition Government in 2013, said the HFC network could have had remediation work completed so that consumers without reasonable broadband in HFC areas could be connected as an interim solution while fibre-to-the-premises was rolled out elsewhere.

"At the point the FttP rollout was completed outside the HFC areas, the HFC network should be replaced with FttP utilising an aerial/underground build approach," he added.

Rod Tucker, Laureate Emeritus Professor at the University of Melbourne and a member of Labor's Expert Panel that advised on the NBN, said while NBN Co had not provided a detailed technical explanation for the delay, it seemed that the root cause was the need to juggle allocation of RF spectrum on the coaxial cable part of the network.

"This has been necessary because Foxtel continues to use part of the RF spectrum for their pay TV services. As a consequence, NBN Co was forced to use a previously untested portion of the spectrum," he said. "Unfortunately, it appears that some coaxial connectors and even some amplifiers have not behaved as expected in this previously untested regime.

Tucker said it was surprising that NBN Co did not see this problem coming. "It seems likely that NBN Co didn’t thoroughly test their HFC technology system before installing it in the field. And it is even more surprising that it took so long for the company to admit that they had a problem," he said. "The fact that they are talking about a six-to-nine-month delay underlines the fact that the problem is serious and potentially expensive."

But he expressed "reasonable" confidence that NBN Co would be able to fix the problem and eventually deliver a DOCSIS 3.1 service that operated as it should. "But at what cost?" he asked. "In hindsight, and taking into account the money wasted when the Optus HFC network was ditched, it may well have been cheaper in the long run for NBN Co to not use HFC in the multi-technology mix."

Robin Eckermann, an adjunct professor at Canberra University and one of the people behind the TransACT network, said he had interpreted the delay as relating to the need to "tighten up" on certain engineering aspects of Telstra's HFC network to assure its performance – "most likely relating to minimising exposure to noise ingress".

"Noise ingress and the shared nature of the capacity were two major considerations when we were confronted with the choice between HFC and FttK/VDSL for implementing TransACT's vision of an open, advanced full-service network back in 1996," he said. "Coax cable has a finite capacity that is shared among all users – so a major determinant of performance potential is the number of users on each coax segment.

"Because the HFC networks were engineered first and foremost for broadcast video delivery, maximum cost-efficiency was achieved by engineering large serving areas, with amplifiers boosting the signals over longer distances. However, coax also works like a giant antenna, picking up interference in the area - and amplifiers boost both the signal and the noise. This sets practical limits on segment length and hence the maximum number of users that could be served from one HFC node."

Eckermann did not anticipate fundamental problems that would undermine NBN Co's intentions to use HFC as one of its delivery technologies – "though installing lead-ins to homes that have never been connected is an additional cost that doesn't generally apply when re-using Telstra's copper in FttN or FttK areas".

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Sam Varghese

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Sam Varghese has been writing for iTWire since 2006, a year after the site came into existence. For nearly a decade thereafter, he wrote mostly about free and open source software, based on his own use of this genre of software. Since May 2016, he has been writing across many areas of technology. He has been a journalist for nearly 40 years in India (Indian Express and Deccan Herald), the UAE (Khaleej Times) and Australia (Daily Commercial News (now defunct) and The Age). His personal blog is titled Irregular Expression.



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