Inside NBN’s fibre to the curb rollout

NBN eyes dual-mode DPUs for G.fast FTTC deployment

Although it is still early days for the roll out of fibre to the curb, NBN says that its efforts to ensure a smooth migration process from the legacy copper network to FTTC have paid off when it comes to end user satisfaction.

But although the company is quick to talk up the performance characteristics of the technology, including a relatively easy upgrade path to gigabit speeds, NBN says that the additional challenges in rolling out FTTC, particularly compared to fibre to the node (FTTN), mean that it’s not ready dump its use of FTTN.

NBN formally launched FTTC services in April. Currently around 1.5 million premises are expected to be connected using the technology.

Connecting homes and businesses FTTC involves two key construction challenges for NBN: Rolling out its Distribution Fibre Network significantly closer to households, and ensuring that the pits where the fibre meets a household’s copper are of an adequate size and in good nick.

Like FTTN, FTTC involves using a home or business’ existing phoneline. However instead of having copper run to a pillar that connects to a powered node (which can serve up to 384 premises), the copper only runs a relatively short distance to a telecom pit on the footpath outside the premises.

In the pit, the copper is connected a distribution point unit (DPU). The DPUs are then connected to fibre. Unlike the nodes used for FTTN, the DPUs don’t require independent power: FTTC uses a reverse power system, relying on the electricity supply of the end user's premises. The reverse power technology relies on a home being only connected by up to 150 metres of copper (with NBN assuming an average of 50m additional within a home, for a total of 200m).

NBN's FTTN rollout on average involves copper lines of 450 metres and in some cases almost a kilometre, cutting back significantly on the reach and complexity of the DFN in areas served by the technology. (The trade-off is that the longer the copper involved, the lower the maximum possible speed for a particular dwelling.)

When the company’s construction partners can use existing ducts to haul fibre it is less of a logistical challenge. But if the ducts are inadequate or don’t exist, the company needs to bore holes to haul the PVC piping through.

The speed for boring tends to average 60 to 70 metres per day — once existing gas, electrical and water conduits have been located (and according to NBN, the ‘Dial Before You Dig’ data can be wildly inaccurate; technology such as ground radar is used before any boring begins).

In some areas where existing services are particularly complicated, in the inner-Sydney suburb of Haymarket for example, that speed can dip to as little as six metres per day.

For FTTC, NBN is deploying up to two DPUs in a single pit, each of which can connect four premises. NBN chief network engineering officer Peter Ryan told Computerworld that the company is finding that “not most but a lot” of the pits either need remediation work to deal with asbestos or are older style pits that are too small to house the DPUs and need to be replaced.

In some cases, the company has also had to build copper extensions from the main pit to secondary pit and then connect to a home.

Ryan said that NBN has put a lot of emphasis on ensuring a smooth migration for those households that are connected via FTTC. Once a DPU is dropped in to the pit, the fibre connection back to the exchange is tested and the DPU is registered to that location and integrated into NBN’s network. The network operator then needs to identify which piece of copper running into the pit belongs to which house.

“Once we’ve identified that and we’ve integrated the DPU back into our network, we literally cut our DPU into that piece of copper,” Ryan said. (Before that happens, however, NBN needs to check that there aren’t any medical alarms or other so-called ‘special services’ relying on the connection, because of the potential dire consequences of an outage.)

Essentially, the FTTC migration process involves a household being connected to two live networks: Even once a DPU is installed and a home connected to it, until an NBN FTTC service is activated, legacy copper services will still operate — a situation Ryan said was “unique”

For FTTC, NBN has used a “self-install” model for end users. Missed appointments by technicians connecting homes to the new network in the past have been a key source of frustration with the NBN migration process. With FTTC, however, end users can be sent the NBN box that provides a connection to the network and switch over when they want to.

“We’ve seen really high success rates” for self-installs on FTTC, Ryan said. The NBN executive attributed that to the effort put into getting construction right as well as to efforts by the retail service providers (RSPs) to make it easier for their customers.

As soon as a modem is plugged in, traffic is directed off the Telstra copper network on to the NBN fibre network. “The moment we detect data flow on that line we complete the activation and close the order,” Ryan said.

“That all sounds pretty complicated but so far we’re seeing a success rate of over 80 per cent… which is actually, for an early stage technology, phenomenal.”

Surveys show a high level of satisfaction with the self-install process, he said.

“In fact, in the early deployments of our technologies… historically what we see is a drop in satisfaction as we get through teething problems and [then] we bring that back,” Ryan said.

With FTTC NBN hasn’t seen that teething process reflected in customer satisfaction, he added.

“We’ve challenged ourselves to deliver a great customer experience from the get-go and thankfully we are starting to see that.”

Preparing for G.fast

Under the government’s current statement of expectations, NBN is mandated to deliver wholesale speeds of 25 megabits per second to all households and at least 50Mbps to 90 per cent of fixed-line premises “as soon as possible”.

NBN says that it is focused on completing the National Broadband Network but that there are viable upgrade paths for its fixed-line services.

The company will begin trials of the G.fast standard over FTTC this year.

“The great thing about [FTTC] is the ease of upgrade to gigabit speeds,” Ryan said. “And it’s not something that’s years away – it’s something that’s live, being tested right now and we will start to deploy into the field next year. That puts us in a position where if the pull from the market demands high speeds, we’ll be able to react very, very quickly and upgrade locally in order to deliver those customer speeds.

At the moment, the DPUs installed by NBN only support VDSL, with connections topping out at a theoretical max of 100/40Mbps.

However, the company is trialing ‘dual-mode’ DPUs from Nokia that will support both VDSL and G.fast, allowing a ‘zero touch’ switchover when there is demand for gigabit speeds (a customer would need to obtain a new modem, but there would be no need to make any changes in the pit).

(Netcomm Wireless and Adtran are also supplying DPUs for the NBN rollout.)

For FTTN, the upgrade path would be a shift to FTTC.

The company would install a small optical line terminal in a node and roll fibre from the node closer to the premises. The method could potentially be used to connect individual premises or a whole area to FTTC.

“We just take the fibre out as far as we want to either to specific houses, businesses or to overbuild areas with an FTTC technology,” Ryan said.

“It’s all about building fibre deeper and deeper and we’ve already done a lot of the hard work going from the exchange to the neighbourhood entry point and then it’s just leveraging off that,” he told Computerworld.

Updated to clarify that the dual-mode DPUs being trialled by NBN are supplied by Nokia.

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Tags broadbandNetworkingnbn coNational Broadband Network (NBN)

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Rohan Pearce

Rohan Pearce

Computerworld
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