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DMT Chips Win 'VDSL Olympics'

The VDSL Olympics results released earlier this week seem to declare discrete multitone (DMT) the winner in the Best Line Code for VDSL competition. But in the opposing camp, vendors supporting quadrature amplitude modulation (QAM) say the results lack real-world viability and won't necessarily hurt QAM in the markets that matter.

The Olympics, sponsored by T1E1, were a series of tests run by Telcordia Technologies Inc. and BT Exact, the research arm of British Telecommunications plc (BT) (NYSE: BTY; London: BTA). Four vendors supplied chips for the tests: Ikanos Communications Inc. and STMicroelectronics NV (NYSE: STM) on the DMT side, Infineon Technologies AG (NYSE/Frankfurt: IFX) and Metalink Ltd. (Nasdaq: MTLK) on the QAM side (see High Noon Arrives in VDSL Battle).

Each lab ran each vendor's chips through a series of mandatory tests, plus a few optional tests (which Infineon chose not to participate in). The results are scattered among 13 reports and some 500 pages.

What's at stake is inclusion in the VDSL standards being completed by three separate bodies, and it's not guaranteed that the Olympics winner will take home the gold in every case.

Ikanos is the most outspoken of the vendors tested, and officials there go so far as to declare DMT the champ not only of the Olympics, but of the upcoming standards bouts as well (see Ikanos Touts VDSL Results). "DMT has won fair and square. We have all the facts in front of us," says Richard Sekar, Ikanos vice president of marketing.

In fact, Ikanos claims carriers are beginning to drop QAM in favor of DMT, the first example being little-known Korean provider Millinet Co. Ltd.. Infineon announced Millinet's choice of QAM-VDSL earlier this week, but this morning Ikanos claimed that Millinet has dropped that deal after seeing the VDSL Olympics results (see Millinet Picks Infineon QAM-VDSL and Millinet Changes Sides). That's how the battle played out when QAM and DMT fought for inclusion in ADSL standards, Sekar says. "When DMT was selected, immediately everybody dropped QAM."

DMT's triumph came in 32 tests of maximum reach at five different speed grades -- some cases were run at 10-Mbit/s symmetric speeds, for example, while others used a split of 16 Mbit/s downstream and 1 Mbit/s upstream. The DMT chips outperformed QAM in nearly every case, reaching as far as 3,450 feet (in one of the 16/1 test cases), compared with best-case figures of 3,000 feet for Infineon's chips and 2,850 for Metalink's.

But Infineon officials point out that the tests, being a T1E1 project, were targeted for the North American market and didn't check any speed higher than 22 Mbit/s. In Asia, 50-Mbit/s technology is already being deployed, with a 10-Mbit/s upstream link, and Japan is talking about speeds as high as 70 Mbit/s.

The Olympics "didn't consider at all what's happening in Asia/Pacific today and what's being deployed," says Mark Tyndall, Infineon vice president of business development.

This leads to an ancillary argument over who's doing what in Korea, where QAM-VDSL has already been deployed. QAM vendors say they can deliver 50-Mbit/s, but Ikanos' Sekar contests that. He notes that in the optional tests, Metalink's QAM chip reached only 40 Mbit/s, whereas Ikanos' was shown to run at more than 100 Mbit/s.

Some Korean carriers have already begun advertising 50-Mbit/s services, and Sekar claims that's the result of Ikanos muscling in on the market. "Generally the QAM guys talk about Korea, but here we are, deploying," Sekar says, citing recent progress with KT Corp. (see KT Deploys Ikanos DMT VDSL).

Infineon officials say they aren't scared, and they don't think they've lost any market share to Ikanos. "We do see the Ikanos solution in some tests out there, but we don't believe it's being deployed in volume," Tyndall says.

Getting back to the Olympics results, Infineon also claims it was handicapped by having older technology. QAM-based VDSL began shipping before DMT-based VDSL, and the chips Infineon submitted were last year's models (the new versions, announced during the Olympics tests, weren't ready in time -- see Infineon, Metalink Intro VDSLPlus). The DMTers, meanwhile, were able to submit chips sweetened for the Olympics tests, Infineon claims.

Sekar has his doubts about that. "Nobody goes to the most important test of their life with an older chip," he says.

One undeniable slip-up came in power spectral density (PSD), where boundaries need to be set to prevent VDSL and ADSL from clobbering one another. Infineon's chip failed to pass several of the test cases here. Infineon officials admit their chip missed the mark but say it did so only slightly -- and that the newly announced chips should solve the problem.

The real test should come today or tomorrow, when the T1E1.4 group is expected to make its line-code decision. In the following month, two other standards groups will wrestle with the DMT vs. QAM question -- the ITU-T Study Group 15 Question 4 and the IEEE 802.3ah task force for Ethernet in the First Mile -- and it's been speculated that they will follow the T1E1 group's lead.

Whether DMT wins could depend on whether the Olympics are the sole deciding factor for T1E1.4. Tyndall notes that the Olympics didn't focus on commercial considerations such as die size and power budget. "That's a very important consideration [because] this is a consumer market and you have to compete with ADSL as well."

Whichever side wins, it's important to note that VDSL still has its share of challenges. Deployment is still relatively slow, particularly outside of Asia. And at the low end, VDSL could soon face competition from speed-enhanced versions of ADSL (see ADSL, Take 2+).

— Craig Matsumoto, Senior Editor, Light Reading

standardsarefun 12/4/2012 | 11:50:53 PM
re: DMT Chips Win 'VDSL Olympics' It seems that the IEEE 802.3ah group has also agreed to adopt DMT for copper Ethernet First Mile.

P.S. A good paper on the results of the T1E1 meeting is now on the IEEE site at: http://www.ieee802.org/3/efm/p...
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