DSL Prime: VDSL's Problems

Crossover and backward compatibility issues mean that ADSL2+ is being deployed even though VDSL should be the superior technology.

by Dave Burstein of DSL Prime and Future of TV [January 12, 2007]

"In 2002 Whitacre directed his chief financial officer, Stephenson, to chop the company's $11 billion in capital spending set for the coming year. Cut it to $5 billion, he instructed, and use the savings to shore up the balance sheet "—Forbes on AT&T's primary strategy.

Joe DeLuca's new chips double VDSL speeds by bonding two lines, and Conexant is pricing them so the doubled line will cost a carrier only $2-3 per month. DeLuca is selling double port modem chips for only $6 more than single port. You also $12 for an extra CO port, the maintenance on the extra line, and some additional Internet traffic expense. Still, over 3-5 years the cost is modest. 3 to 7 million of AT&T's targeted 19 million Lightspeed homes are not getting the targeted 25 megabits down with current equipment. Paul Reynolds of BT also tells me he's interested. Plenty of extra copper most places, as Bill Smith identified 57 percent unused at BellSouth. At least 6 months and probably more from chip samples to a field-proven solution for AT&T.

Dayanidhi Maran of India has just raised the minimum download speed for DSL to two megabits, recognizing that anything less than that isn't truly broadband in 2007. Standard video needs almost that much, so it's a practical minimum. The increased demand persuaded Alcatel to promise a $600 million investment in India and exemption from layoffs. That means the U.S. will receive a higher share of the coming Alcatel-Lucent layoffs. Long before the Lucent deal, Serge Tchuruk said the only thing preventing heavy U.S. layoffs was fear of AT&T reaction while Lightspeed was already a year late. A year later, still bugs to swat and missing features, but the Alcatel employees are now very, very afraid.

Nothing in this issue about "net neutrality" as a courtesy to "Blue", an industry veteran once a friend. He unsubbed saying, "You've finally lost it . . . please drop." Much to come, as I find myself with 15 minutes of fame in the middle of this one, even doing an ex parte.

At the end of this issue is a review of stories in the works, some of which may be interesting enough for you to comment. Some of them are actually posted on a "drafts" page. It's an experiment in journalism with reader's help. I've also included excerpt's from Chris Anderson of Wired on how a publication can be "radically transparent." Ideas welcome.

Correction: VDSL "Crossover" Not Close
ADSL equivalence mode and interoperability disappointing
VDSL is working well for highspeed service from the basement, deploying rapidly in Japan. From the neighborhood node, DT has 3M homes passed and AT&T over a million, with both intending to rapidly expand. So the niche will expand, but I have been unable to find a carrier regularly using VDSL gear for customers over 5,000 feet, despite a VDSL standard designed for that choice.

Yet another carrier has told me DSL Prime's enthusiasm for an early switch to all VDSL2 service is premature. "I'd never get 72 ports on a line card with VDSL2, and the power problems are hard to solve," their DSLAM designer tells me. Density, heat, power are proving very resistant to improvements. Prices are staying high, 2 or 3 times the $6 or less ADSL2+ chips can go for. TI isn't competing for the high end, and several other announced chips have not come to market.

From 5,000 to 12,000 feet, the goal was equal performance. The actual VDSL chips were considerably slower (up to 20 percent) to customers at those ranges. Only one profile (8b) allows full downstream 20.5 dBm power; all profiles reduce power by several dB and result in less maximum performance.

"Deployable interop will take more time to settle," an chip engineer laments. "All vendors are upgrading VDSL2 firmware rapidly. Production designs are changing rapidly." Carriers deploying now must use modem and DSLAM chips from the same vendor, and may be locked into that vendor for several years to maintain compatibility. The DSL Forum and UNH are working on the problem.

My prediction, "20 percent of dollar volume will be VDSL by the end of 2006, I believe," is almost surely wrong. Currently, only deployments under 5,000 feet are going to VDSL. Those with a substantial portion of lines over 5,000 feet are going for ADSL2+.

Conexant Looking to Resolve VDSL Problems
New chips and bonding
They're smiling in Red Bank and San Diego. The new Conexant VDSL chips are sampling and headed for production, with positive responses from customers including Alcatel. The Accelity-2 DSLAM chips can support a higher density port line card, DeLuca claims, and are priced at $12/port. They've measured the ADSL2+ performance at within 10 percent of comparable ADSL2+ only chips. They support bonding, and claim complete non-blocking performance. The four new cpe chipsets are priced from $24 to $30 each in volume quantity, with the higher price including two bonded ports. DeLuca believes the on-chip processors are fast enough to eliminate the external network processor that currently adds to the cost of most IPTV grade modems. Both sampling now, production soon. Field tested bonded gear sometime after that.

Copyright 2007 Dave Burstein.
The DSL Prime Newsletter is reprinted with permission.

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