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

Stuart Corner
Wednesday, 10 November 2010 09:13

Business IT - Technology

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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