itb-nz logo
Story image

Evolution to Fibre to the Home – the Chorus way

01 Oct 2009

In its final plan for ultra-fast broadband the government rejected Telecom’s proposals, but it didn’t shut the door on the incumbent. In the days following the announcement ICT Minister Steven Joyce made it clear that the Invitation to Participate will allow for both national and regionally based network proposals.The sticking point for Telecom is that if it wants to participate at an infrastructure level, it can’t offer the retail services on the same network unless it structurally separates its network division Chorus.But setting aside this – admittedly major – stumbling block, the revised plan has made it technically possible for Chorus to say that its Fibre to the Node (FTTN) roll-out is a logical stepping stone on the path to Fibre to the Home (FTTH) for 75% of the population – the government’s target for ultra high-speed broadband delivery.This is because the government is now flexible about network design.Point to Point (PTP) vs Passive Optical Network (PON) deploymentsPut simply, a fat backhaul fibre pipe is rolled out to an aggregation point (it could be an exchange or a cabinet). If individual fibres are deployed to individual premises, that’s a PTP deployment. If an optical splitter is used to divide the bandwidth inside a single fibre so it can be parceled out among several premises, that’s a PON deployment.In the draft proposal released in March there was a declared bias in favour of PTP over PON. But the final plan, released last month, states that as long as there is provision for open access, the government is essentially agnostic about network design:“The forms of open access at the passive layer are inextricably linked with the type of network architecture selected for the passive layer. While Passive Optical Network (PON) fibre access network architecture does not lend itself to unbundled line access as naturally as the Point-to-Pont (PTP) architecture, there are methods for providing open access to PONs and further methods are being developed.”Chorus PON deploymentChorus favours PON deployments because the structure of its network is hierarchical, and PON lends itself to a kind of trickle-down approach.There are four different types – or Tiers – of exchanges in the Chorus network:Tier 0 – contain data centres and support highly centralised functionsTier 1 – highly interconnected, accommodate regionally centralised functionsTier 2 – large exchanges that serve no more than 120,000 customer connectionsTier 3 – suburban exchangesIn the new FTTN network, Feeder Cables run from Tier 2 and Tier 3 exchanges. These are fat fibre pipes that are deployed to roadside cabinets. From these cabinets run Distribution Cables which deploy individual copper pairs to homes and businesses.In a Chorus PON network, additional fibre aggregation cabinets would be built, which would push out fibre directly to the home – see the above illustration, based on an area in the Auckland suburb of Avondale.In a PON deployment a fibre aggregation cabinet would house passive splitters that divide the light in one fibre connection and parcel out the bandwidth in equal amounts. The number of homes served by a single fibre connection can vary, but the most common PON deployment is 1-32 or 1-64.Dhyberg acknowledges that the Feeder Cables are not designed to connect up customers – they are designed to connect an exchange to a roadside cabinet. So new infrastructure would have to be built, but he points out that Chorus already has the ducting in the ground and he says digging up the street to lay cable is about 70-80% of the cost in deploying FTTH networks.CompetitionThe government is now satisfied that PON can be used to deliver competition at the “dark fibre level” – a competing telco could put its own optical splitter at the aggregation point in a fibre network, just as it deploys its own DSLAM in a copper network.“In these cabinets you could have multiple splitters – one for Telecom, one for TelstraClear, one for Vodafone,” says Dhyrberg. “All they need to do is have their own bit of feeder fibre from there to any one splitter.”This means there is no technical reason that competition can’t occur at the basic infrastructure level, but there is an economic one. The FTTH/PON network Dhyrberg advocates would see the addition of new cabinets that would become aggregation points serving a smaller number of users. In other words, an exchange serves thousands of users, a cabinet serves hundreds and the mini- cabinets that Chorus is proposing will serve tens of customers.“Once you’re getting down to only delivering customers to 100 metres, the number of customers is quite small, so it really becomes an issue of the economics of it,” says Dhyrberg.When asked if a Chorus FTTH network could deliver competition, Dhyrberg replied: “To what extent is that policy objective paramount versus cost? You can do anything with the right amount of money. Any of these issues is absolutely solvable; it comes down to how much you are prepared to pay for competition.”Transition from copper to fibre servicesDhyrberg says that ISPs deliver the vast majority of their services over copper, so transitioning to fibre is likely to take some time. “If you came along and said right, everyone is swapping over to fibre; everyone would be in an absolute flap because you have to rebuild your systems so you could deliver it over fibre.”The ideal would be to provide a concurrent copper and fibre service, something that Chorus is already onto.“We’ve got our guys with their thinking hats on, thinking about how we design new cabinets that will give us this dual copper and fibre capability, and we’ve got Eaton (the company building the cabinets for the FTTN) working on plans now. I’ve seen their concept plans and they look quite clever really,” says Dhyrberg.Chorus is also working with Ericsson to use its micro-ducting technology that enables copper or fibre to be blown through underground ducting. They’ve trialled the technology on new subdivisions and they’re tackling the first brownfield deployment in the Auckland suburb of Manurewa this month.Vector is undergrounding its power cables, which means the telephone power poles will disappear, so Chorus is taking the opportunity to install Ribbonet micro-ducting – little plastic tubes or ducts – from the street to the house.Ericsson managing director Jeff Travers says once the tubes are in place, an engineer will go into the home and use a vacuum gun to blow copper down the duct – a exercise that only takes “a couple of minutes”.Dhyrberg calls the process “beautifully simple”. He estimates the cost to deploy the micro-ducting is around $1000 a home, and there are 1100 houses in the Manurewa brownfield trial. He says the cost is more than they would have spent using traditional methods, but it’s future-proofed.“If someone comes along and says ‘I want one of these groovy new services that you get delivered over fibre’, all we have to do is send a guy around, he pulls out the piece of copper out of the tube and blows fibre down the tube. You don’t have to dig up the street; it’s already been done.”

Travers says the technology was developed many years ago for British Telecom, but it’s only been installed to date in Scandinavia and some Asian countries.“Most of the world is not going much further than FTTN or Fibre to the exchange themselves. Going FTTH is early days all over the world.”