Home Business IT Business Telecommunications 400Mbps VDSL rings touted as cut-price alternative to FTTH


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400Mbps VDSL rings touted as cut-price alternative to FTTH

The Coalition might have another weapon in its battle to push alternative technologies against the Government's $43b, predominantly FTTH, National Broadband Network: a UK company claims to have technology that can deliver up to 400Mbps over existing copper, at less than 10 percent of the cost of FTTH.

The technology, from Genesis Technical Systems, exploits the topology of the local copper access network to overcome the distance limitation of VDSL2. According to Wikipedia "VDSL2 deteriorates quickly from a theoretical maximum of 250Mbps at 'source' to 100Mbps at 0.5km and 50Mbps at 1km'¦From 1.6km its performance is equal to ADSL2+."

In most urban telephone networks around the world, groups of homes, up to 50, are served by street corner pillars, or distribution points (DP) generally less than 150 metres from connected homes and two pairs run to each house. From this DP the 100 pairs are connected back to the Exchange, over distances up to several kms.

There are two distinct components to the Genesis technology: standard DSL bonding and its proprietary ring architecture. Bonding techniques are used so that instead of each subscriber having a dedicated pair back to the exchange, all the pairs from the exchange to the pillar are bonded together.

So for example if the pillar is close enough to the exchange to get ADSL2+ at 10Mbps, and 24 pairs are combined, 240 Mbps, downstream can be delivered to the pillar to be available to all houses connected to that pillar.

In the Genesis system there is a VDSL2 modem that is connected to the 'first' house on the pillar over one of its two pairs. In that house is what Genesis calls its home gateway - a two port VDLS2 modem that terminates the first pair from the pillar, regenerates the signal and sends it back down the second pair to the pillar.

In the pillar a jumper connects this pair to the first pair of wires going to the second house and sends the signal back out. Each and every house is connected in this way creating a ring in which the longest distance the VDSL2 signal has to travel is the sum of the distance between the pillar and two 'adjacent' houses - perhaps 300 metres maximum.

And because this is a ring topology signals can travel in both directions, doubling the bandwidth available at each house compared to a singly VDSL2 connection.


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According to Genesis the key to making its technology commercially viable is that it is able to operate without the equipment installed at the pillar needing its own power supply.

Genesis VP and CTO, Stephen Cooke, told ExchangeDaily: "We can power our pedestal based unit - we call it a convergence node - from the exchange, but a 24 port remote mini DSLAM [to support standard VDLS2] would need mains power, fans, batteries, heating ventilation and air conditioning. We don't need that."

He said Genesis had estimated the cost of its technology at five percent of FTTH in urban areas. "It could be as high as 10 percent but it's unlikely to be more. In rural areas we are probably one percent of the cost of FTTH."

Genesis is claiming bandwidth of "up to 400Mbps". This is the total of upstream and downstream bandwidth and Cooke said: "We have total control of how that bandwidth is split, and that is the subject of one of our patent applications."

The available bandwidth has to be shared between all users on a ring and Genesis recommends a maximum of 16. According to Cooke, "Our technology is flexible enough that you can put any number of houses between those end points economically but we recommend that you limit it to about 16 because each house introduces a little delay."

He said also that QoS capabilities were built into the technology so that users who had paid for a premium service would receive latency-critical applications like voice and video with priority over other application.

"We use an existing technology from optics RPR- resilient packet rings - that was built to encapsulate ethernet. We took that and put it over copper. It supports efficient multicast and quality of service.

"If users are all using high demand services, yes there will be contention but if they are using a mix of traffic those that have paid for higher grade of service wil experience no degradation.


Cooke said that the technology could also be used to improve bandwidth over copper in rural areas where the network topology is rather different and distances from the exchange much greater.

"In rural situations the cable comes out of the exchange, goes down a road to the first group of houses and then the same physical cable continues on down the street to the next group of houses with a DP [distribution point] at each group of houses.  That situation allows us to re-bond the signal at each DP, thereby 'saving' the available bandwidth at the first DP and passing it along to the DPs further down the road'¦.We could not achieve the 400Mbps that we can in more urban/suburban environments out to 7km from the exchange, we should still be able to achieve 5-10Mbps which would be much better than the zero bits/second that they can get now."

The technology is still some way from commercialisation. Cooke told ExchangeDaily: "We have finished our home gateway prototypes and shown them in two major European telco labs and shown that the bandwidths we claim our possible.

"The next stage is lab trials. We have given this to the major European incumbent telcos for them to play with in their labs without us watching. If they like it they will trial it in their networks."



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