FEATURE FTTDP
which reduces the available bandwidth. Acceleration technology, in particular vectoring, must be employed. ‘Te higher the frequency, the more cross talk that you are going to get, so it’s a given that G.fast will require vectoring as part of the solution,’ said Kelly. Alcatel trialled G.fast technology in 2014 and ‘with G.fast at a distance of 100m we managed to get just 60Mbps. Tat’s ridiculously low, and the reason for that was cross talk. When we added vectoring into the mix, we actually got 500 Mbps on the same cable. Tat’s a big difference,’ said Vanhastel. Conventional deployment models are not
always suitable for complete coverage as Vanhastel highlights: ‘FTTH, FTTC, and FTTB were the three main models until maybe a year ago. Now, with the emergence of VDSL2 vectoring and G.fast with vectoring, we’ve started to see these “in-between” models. All these FTTdp models are appearing because operators simply need them; they need toolkits with all the solutions, so they can select the best one’. However, G.fast only delivers high-speed
broadband over a relatively short distance – typically no more than 200 to 300 metres – and so one distribution point can serve only a relatively few subscribers. Tus, the challenge of being able to get a return on the investment remains, even with fibre to the distribution point, as Kelly explains: ‘At the distribution point, I still need power for the equipment. I have typically got somewhere between eight and 25 subscribers to spread the cost of the installation across. You can’t put a cabinet out at that location to address 20 customers you’ll never get a return on your investment.’ ‘Adtran have been pushing sealed outside plant
DSLAMs for 12 years,’ Kelly continued, ‘a fully sealed waterproof piece of equipment that can be put on a pole or it can be deployed underground.’ Te big benefit with both of those applications is that you don’t need a cabinet’ said Kelly. One of the biggest costs with deploying large cabinets is the power required, as Kelly explains: ‘In the UK, the installation of a local AC power supply can cost anything from £3,000. If there are civil engineering works and road digs involved, anything up to £20,000. If you had to incur that cost to address between 8 and 20 customers you would never get a return on that investment.’ Te answer is equipment that consumes less power and is less costly than deploying a large cabinet. Te proposed solution to this is reverse
powering: ‘Te device that goes into the customer’s premises to terminate the broadband signal has the capability of providing a small current back over that line, which assists in powering the equipment,’ said Kelly. ‘Tere is a lot
24 FIBRE SYSTEMS Issue 3 • Spring 2014
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The challenge of being able to get a return on the investment remains, even with fibre to the distribution point
of focus within the industry to see if reverse powering will be a means of sidestepping that install power cost.’
FTTdp fits with fibre deployment strategies ‘FTTdp with G.fast is seen as complementary to a longer-term FTTH strategy because ultimately what they are doing is pulling that fibre closer and closer to the customers,’ said Kelly. He continued ‘Tey [service providers] are doing it in an incremental phase that allows the operators to get a return on their investment. So they can take the investment in smaller chunks, recover a return, and then slowly get to that FTTH phase.’ Tis provides the advantage of being able to reuse the existing fibre optic cable infrastructure that had been deployed for FTTC or FTTdp. ‘Tese are not wasted or lost investments; you can reuse a big part of those investments when you go FTTH. If you bring fibres to the street corner, for cabinet deployment, obviously you can reuse that fibre,’ said Vanhastel. A further advantage of FTTdp is that there is
no need physically to gain access to someone’s home in the course of the deployment. ‘In some
countries, this is a major headache. It is a big part of the operational costs: for example, the person is not at home, so you have to make appointments. It can be very expensive to enter the home,’ said Vanhastel. Kelly has heard similar problems from Adtran’s customer base: ‘Quite oſten a lot of the challenges are very little to do with the technology itself and more to do with simple things like way-leave applications, planning permission, and missed customer appointments. Some of the operators that we speak with, talk about missed customer appointments in excess of 30 per cent.’
Longevity? Te FTTH council has advised that only FTTH is a ‘future proof’ solution, so if FTTdp is seen as a complementary solution to the ultimate FTTH strategy, its lifespan will depend on the applications. Few consumers upgrade just for the sake of it – mostly they wait until they experience a significant worsening of service. Kelly gave an example of some European
operators that have undertaken FTTH deployments and are currently offering 100Mb services to customers: ‘When they average usage across all customers on their customer base they are typically seeing maximum average usage in the region of half a megabit per second (500 kilobits).’ Although the figure might be slightly misleading because usage patterns vary depending on the other services that end users have available, the question remains: how long will it take for 500Mbps speeds to become insufficient? ‘It’s a tricky one to answer. With normal usage patterns and even taking into account things like 4K TV, I firmly believe that there is at least 20 years in the G.fast technology before it begins to come under pressure.l
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