Carl Weinschenk spoke with Arun Hiremath, the director of central office marketing for Ikanos.
Digital subscriber line (DSL) technology has been on the endangered species list for years. It has one attribute, however, that keeps vendors and service providers hard at work: It is in most homes and businesses in the world. Arun Hiremath told IT Business Edge blogger Carl Weinschenk that vectorized VDSL is the next step for the technology. DSL, Hiremath said, is far from dead.
Weinschenk: So, I take it, you don’t feel that DSL is on the way out.
Hiremath: There was a feeling that DSL was almost done. What happened during the last couple of years was that the use of vectoring -- a crosstalk-canceling technology that was thought to be a very exotic -- became more feasible. Ikanos was one of the pioneers that showed that it can be done for a reasonable cost. During the last year most of the carriers have seen that vectoring can be used for the mass market.
Just to give an idea of the delta: VDSL came along in 2004 or 2005 and held the promise 100 megabits per second down and 50 megs up to a half a kilometer range. But when carriers put it in the field, crosstalk drove the performance down drastically. It wasn’t meeting its promise. Vectoring VDSL cancels that crosstalk and allows you to get the performance very close to what you get in a single line performance with nothing else on the line. It’s called effects-free.
Weinschenk: So that allows it to continue to be a useful tool.
Hiremath: What happens is you have fiber termination – fiber-to-the-node or micronode, fiber-to-the-curb or basement or all the way into the house – using the old copper that is vectorized. That is one-tenth the cost of an all-fiber approach. In the Americas, AT&T’s U-verse and Verizon’s FiOS are two examples. Verizon is using fiber-to-the-home and AT&T to a point just outside the home. With vectorized VDSL you get 100-plus megabit per second downstream at half a kilometer, and about 40 megs up. We have shown it is possible. We have shown it in the lab using real-world cables.
Weinschenk: Is it true that an apples-to-apples comparison is not possible, though, because this only is being done in the labs?
Hiremath: How the fiber deployment plays out depends on how the specific carrier deploys. If they have used GPON and split bandwidth for different users from the OLT it will be less than 1 Gig for each customer. You can get more than a gigabit if you have dedicated fiber to every house. Typically, if you use regular GPON and other technologies that split bandwidth to various users, you can anywhere from 30 megs to one gig.
Weinschenk: So what does the decision-making process look like?
Hiremath: There are two major factors affecting their decision. There is no dedicated fiber to every household. So it takes two things to create that: money and time. We discussed the money element. It’s that one to 10 ratio. The time element involves logistic challenges to reach every household with every fiber. For some single family houses there are challenges for digging the street. In cities the challenges are even more severe and if you are wiring apartments getting fiber to every house becomes a bigger challenge still.
Weinschenk: Are you saying that vectorized VDSL is the equivalent of fiber, or just that the gap is closing?
Hiremath: The gap between the two is much less. For example, before vectorization, 100 meg sustained at a half kilometer was almost unthinkable on cooper. Now in many places it can be done. And in many countries, including the U.S., ist is common to have more than one twisted pair of copper in the home. You now can combine the two pairs to get double the bandwidth. Channel bonding becomes more important because you can cancel the cross talk.
Weinschenk: Is this happening?
Hiremath: Vectoring is part of an ITU standard agreed to three years back. The carriers are now going to start seeing it as usable in mass deployment.
Weinschenk: What is coming next?
Hiremath: There is a new discussion in the technologies bodies for how to get one gig over copper, perhaps for very short distances. Perhaps just from the pedestal onward. The goal is to use all these techniques and expand the frequencies to enable the use of copper for the last 100 meters. It’s called G.fast.
It still is in the standards bodies. We expect it to become a standard at the end of 2013 or in early 2014. Typically after standardization we see products in the field in 18 months, so that takes us to the latter part of 2015 before we see the first products with G.fast. It will be at the central office and in CPE gear.
Weinschenk: So DSL – through vectorized VDSL – is having a bit of a rebirth, in your opinion.
Hiremath: We see announcements from major carriers that say they are going with vectored VDSL. The National Broadband Network of Australia said that they wanted to go all the way with fiber but changed it a month or so ago and now are saying that they will save time and money by changing to vectored VDSL. Deutsche Telekom also said that they are using vectored VDSL for their network in Germany. And there are many other announcements during the last six months saying that vectored VDSL is what makes sense.