Spoke:
I realize that this article is very dated but it explains that:
“Beyond 12 MHz — and in reality you don't even get that at the loop lengths we're talking about — it's not a service that we think is going to be very valid,” he said. “We're not really interested in saying ‘what can you do at 700 meters?’”
Based on this article, it appears to me that 12 MHz was compared because that is the profile for longer loops and is what the Carriers are using in the US and Canada.
There would be no reason to compare 30 MHz applications if that spectrum is not being used.
VDSL2 standard put on fast track for U.S. market
By Vince Vittore
May 9, 2005 12:00 AM
The next gen IP network needs to be able to handle a wider range of services and applications - and service providers are going to need intelligence at the IP network core. Get more info in this live Telephony Webcast: Thursday Jan. 24 2:00 PM ET | 11 PM ET.
For a number of reasons, not the least of which was a drawn-out debate over line coding that stalled initial phases, it took the better part of 10 years for ADSL to go from the lab to a mass consumer product that could deliver 3 Mb/s for Internet access. And even now, that speed is more the exception than the rule. The time frame for VDSL2, which moves into a critical two-week development period later this month, should be less than half of that if U.S. carriers get their way.
Very high-speed DSL (VDSL) technology in its original form has been available for at least six years, and, in fact, at one time was thought to be the solution for Bell companies' video plans. However, because the first version of the technology did not go through the traditional standardization process, few vendors developed products, and only Qwest, a handful of independent telcos and, more recently, some select Asian carriers, ever deployed the technology.
VDSL2, which promises speeds of 30 Mb/s and beyond, is starting life in an International Telecommunications Union (ITU) standards committee, and most of the technical debates have been settled. More important, both SBC Communications and BellSouth, along with a group of CLECs, are pushing for the technology as soon as possible. In fact, both RBOCs are perhaps more significantly involved in the development of the VDSL2 standard than most other technologies. Some of that stems from the fact that they want to use the technology as a sort of natural expansion of their ADSL deployments.
“In pushing for VDSL2, there are a number of objectives,” said Ralph Ballart, vice president of broadband infrastructure and services for SBC Laboratories. “One is compatibility with ADSL. That's reflected in the commitment we made to use [discrete multi-tone line coding]. The standard has been created with an eye to getting rapid VDSL2 compliance by the chip vendors.”
What makes the development of VDSL2 and ADSL significantly different, though, is the competitive dynamic faced by telcos. In the mid-1990s, when ADSL was still in its formative years, cable operators had vague designs on providing residential voice service but no real solid business plans, voice over IP (VoIP) was barely in the hobbyist phase and cable modem-based Internet access was a mere novelty for a lucky few. Fast forward a decade and cable operators are gobbling up chunks of the residential voice market fast, more than 1000 service providers are vying for attention in the VoIP market and cable modems have continued to hold a 2:1 ratio lead on DSL for broadband access. In order to respond, the largest telcos have greatly accelerated their video deployment plans. And in order to do that, VDSL2 can't come soon enough.
The urgency is so great, in fact, that some vendors are already preparing “pre-standard” VDSL2 equipment, hoping to tweak the gear when the standard is approved.
“I believe that the VDSL2 chipsets will appear as soon as the standard is closed,” said Ed Eckert, director of strategic standards for chip vendor Ikanos. “We're ready to go now.”
For its part, SBC will begin testing VDSL2 equipment even if the standard is not 100% complete, as long as future upgrades can be handled by uploading firmware to the chipsets, Ballart said. In addition, the company wants vendors to begin interoperability testing soon but won't stall deployment plans without it.
“We'll be expecting that we have a substantial effort around interoperability after the standard is final, but we're not going to wait for that,” said Gene Edmon, executive director of broadband for SBC Laboratories.
Several executives involved in the standardization process say the desire for VDSL2 is so strong that some carriers in particularly competitive markets won't wait even for the close of the standardization process.
“One result may be that people don't worry about standardization, particularly some of the CLECs,” said Ken Madison, senior product marketing manager of Centillium.
“If they can deploy in three months and provide 25 Mb/s symmetrical service, they'll do it.”
And like the early deployments of ADSL, carriers won't kill time waiting for full interoperability, he added. “I don't see any carrier daring to buy CO equipment from one vendor and CPE from another because interoperability is not going to be there for another two or three years.”
So what exactly will SBC, BellSouth and others get out of VDSL2 that they don't have with the various flavors of ADSL? In a word, speed. VDSL2 as it currently stands will have at least three different versions. In one, which calls for a spectrum allocation of up to 12 MHz, carriers will be able to provide up to 30 Mb/s over loop lengths up to 6000 feet. Beyond that, there's a significant drop off, but the profile is such that most believe it will gain most significant traction among U.S. carriers.
“You basically kick ADSL's butt up to 6000 feet and keep up with it after that,” Eckert said.
Another version will allow for longer loop lengths — but not nearly the same speed — and still another flavor, which calls for spectrum allocation up to 30 MHz and may be among the last to reach standardization, will push speeds to 100 Mb/s on both the upstream and downstream paths. The latter, however, has extreme limitations in loop length and is of little interest to SBC, Edmon said.
“Beyond 12 MHz — and in reality you don't even get that at the loop lengths we're talking about — it's not a service that we think is going to be very valid,” he said. “We're not really interested in saying ‘what can you do at 700 meters?’”
In SBC's Project Lightspeed plan, fiber will be run to remote cabinets, where VDSL2-based gear will sit. The goal in most cases is to get cabinets within 6000 feet of subscribers and be able to provide anywhere from 20 Mb/s to 25 Mb/s of total bandwidth. At that level, the company could offer one high-definition video stream, perhaps two standard-definition streams and still have plenty of bandwidth left for high-speed Internet access and voice.
“There's no question that VDSL2 will allow speed in excess of that,” Ballart said. “It's nice to know that, but typically, we're talking 20 to 25 Meg for customers served out of those cabinets. Also there will definitely be MDU deployments [where cabinets are deployed in the basement of buildings]. The total strategy around that is stuff that is still being worked through.”
Though others are deploying fiber deeper into the access network, there appears to be a general agreement among U.S. and Canadian carriers to only operate up to 12 MHz right now, Eckert said.
“Instead of spending the committee's time arguing about what to do above 12 MHz, they're saying ‘let's do what we need now,’” he said. “Qwest is quite interested, and they've made it quite clear that they want this done in May.”
From May 16 to 27, the ITU will host meetings to take the next major step in the process. During those gatherings, the VDSL2 specification is expected to begin the final steps toward completion, with ratification scheduled for later this year. And while carriers often support and observe such proceedings, VDSL2 is getting what can only be characterized as “strong encouragement” from numerous service providers.
“We are getting enough pull from the service providers that we will have positive results [from the meetings],” Madison said. “It's a formidable task, but it's doable.”
Like in most standards process, getting the final pieces of the puzzle in place is a mix of politics and technology debate. At the same time, the industry is looking to the standard to be more than a stopgap measure.
“With VDSL2, I think you're going to see a technology that is going to have a long shelf life,” Madison said. “VDSL2 has everything one needs to deploy any application I can see.”
