Vectored DSL - How It Works

Cancelling noise can double short loop speeds. Telco networks are generally built with 25 lines joined together in a binder like the picture. Each active wire generates crosstalk "noise" which interferes with the lines around it, reducing their speed. Cancel the noise and the lines can run faster. In practice, speed doubles to 70-100 meg down, 10-40 meg up, over short loops up to about 300 meters. Up to about 100 meters, a related standard G.fast, promises 200+ megabits. Bond two pair and you inexpensively (less than $125/home) double the speed again. As loops get longer, the crosstalk noise becomes less of a factor and the speed is limited more by the resistance of the copper wire itself and other kinds of noise, like AM radio. Over about 1,000 meters, vectoring has almost no impact. So vectoring matters if and only if you have a box fairly close to the customer. These "neighborhood nodes" can be small; you can connect 48 homes with a "pizza box" DSLAM. The boxes themselves are usually connected by fiber to the exchange. "Fiber" is a magic word and a brilliant AT&T lobbyist came up with the name "fiber to the node," FTTN. It worked; AT&T's node DSL build, U-Verse, got major government concessions. Stanford Prefessor John Cioffi and his former student George Ginis developed the idea back in 2002. The name comes from the vector mathematics used to calculate the noise cancellation. They couldn't demonstrate at the time because the calculations for 25 pairs running at 100 megabits were impractical. As Moore's Law improved chip performance, demonstration systems from ECI and Lantiq began showing in 2009. By 2011, Alcatel demonstrated production-oriented systems that were tested in 2011-2012 at carriers including Swisscom and Belgacom. The results were outstanding, confirming the 70-100 meg speeds. European carriers including Deutsche Telekom and Telecom Italia abandoned fiber plans and switched to the much cheaper vectored DSL. By late 2012, numerous problems emerged from early field trials. Carriers including Belgacom and Deutsche Telekom decided to delay substantial deployments until late 2013 or even 2014. Everyone is confident the problems will be quickly resolved with minor changes in the gear and the software managing the networks. Deutsche Telecom remain confident of deploying 12M to 24M lines in four years. The Germans in particular are anxious to deploy quickly because the cable guys are kiling them. DOCSIS 3 in Europe can offer "up to 200 megabits" down because EuroDOCSIS uses 8 MHz channels. Kabel Deutschland's standard offer is "twice the speed of Deutsche Telekom DSL for the same price." Kabel committed to early deployment of gigabit DOCSIS, perhaps by yearend 2013. Deutsche Telekom's estimate of cost is EUR 6 billion for 24 million homes, less than $450/home passed. Telecom Italia and AT&T have lower estimates. I use a figure of "about $400" for short discussions. VDSL DSLAMs sold for an average price of $38/port in 2012, although if you aren't buying in the millions you'll likely pay a much higher price. Adding vectoring raises the bill of materials by only a few dollars per port, but first to market Alcatel is looking to charge a 100% premium for vector. As Huawei, Adtran, ECI, Calix and others ship systems, the price will come down. Those DSLAMs need to be installed in field cabinets and connected by fiber to the exchange. Most customers need new modems. But at $50/month, three year revenue for VDSL is $1800. The investment is so quickly paid off it fits within the typical telco capex budget. The saving compared to fiber is at least $500/home and possibly $1500-$2000/home. Thursday, 04 April 2013 16:03 First tier telecomm accessories supply Original Article here