Next-Gen ADSL Comes into View

ADSL2 and ADSL2+ Products Expected this Year

Next-generation ADSL equipment expected to hit the market late this year could help rev up telco implementations of video services.

"They will certainly help enable video a great deal," says Tom Starr, president of the DSL Forum. "This is allowing much higher bit rates to all the loops."

Starr is referring to technologies called ADSL2 and ADSL2+.

The original ADSL standard, on which installed equipment is based, specifies a downstream bit rate of 6mbps and a reach of around 10,000 feet.

The ADSL2 standard (also known as G.992.3), approved by the ITU last October, offers "modest improvements" in bit rate and longer loop reach, and other added features, says Starr. The highest bit rate specified in this standard is 8mbps downstream and 800kbps upstream. The reach on ADSL2 depends upon multitude of factors, but for basic service rates of 384kbps downstream offers reach of about 16,000 feet.

Other benefits of ADSL2 beyond rate and reach include increased robustness against RF interference, bridge taps and more. ADSL2 also provides an expanded line diagnostic capability. When there's trouble, the modem can measure attenuation, signal-to-noise ratio on both ends of the line, and more. Improved power management through ADSL2 means the equipment goes into a sort of sleep mode when no traffic is running over it, which results in a dramatically reduced power requirements and less heat in the cabinet, which is particularly useful in remote terminal applications, says Starr.

Yet another next-generation version of ADSL, called ADSL2+ (or G.992.5), also has been defined in the DSL Forum and ITU, notes Starr. That recommendation, which builds upon ADSL2, was consented to by the ITU in January. ADSL2+ offers rates of up to 20mbps downstream and 800kbps upstream at relatively short loop lengths.

An addendum to ADSL2+ called annex L provides about 2,000 feet additional reach over the first generation ADSL, says Starr. "By the end of the year we will have this extended range annex L, which on long loops gets you out to about 18,000 feet, which is the length at which, in the U.S., you end up with loops with loading coils," says Starr. Since loops with traditional loading coils are not suitable for DSL, annex L takes ADSL about as far as it will ever be able to go, explains Starr.

Starr says most vendors will wait and deliver ADSL2, ADSL2+ and annex L all in the same products at the same time. "Maybe some will come out with ADSL2, that's possible, but some will just make the big leap," he says. To pave the way for those products, the DSL Forum is staging interoperability demonstrations of ADSL2 chipsets. The group already has done one such demon, and expects to do another June 23 at the University of New Hampshire Interoperability Laboratory.

Matthew Byrd, vice president of marketing at Net to Net Technologies Inc., says the company's chip vendor, GlobespanVirata Inc. has reference designs for its ADSL2 chipsets available now and chipsets should be ready later this year. That means systems using those chipsets should hit the market in the fourth quarter of this year or the first quarter of next year, says Byrd.

Net to Net has Ethernet-based ADSL equipment on the market that can deliver 10.5mbps downstream. That version of ADSL uses S = 1Ž2 or U0 (upstream zero band) technology to get the additional upstream bandwidth over ADSL's traditional 6mbps downstream, he explains. "That's part of the currently available and ratified ADSL standard," he says.

Next Level Communications also sells a 10.5mbps downstream ADSL solution, which it markets as ADSL+. The company came out with that product nearly a year ago, says Geoff Burke, director of marketing services. At least a dozen customers have purchased or are now testing that ADSL+ system, which can support two streams of video as well as high-speed Internet and voice services.

ADSL+ is not a standard and does not relate to work out of the ITU or the DSL Forum. "ADSL+, as Next Level defines it, is an enhancement of the ADSL standard," says Burke. "It allows greater downstream capacity, optimized for video. It's compatible with VDSL, ISDN ... because it's strictly aligned with the ADSL standard." Burke says ADSL+ does not extend the spectrum outside the range of ADSL, but says enhanced spectrum defined in ADSL2 and ADSL2+ is not compatible with ISDN.

Still, Burke calls the ADSL2 standard "interesting," but adds that Next Level's ADSL+ implementation today through its chipset allows ADSL to operate outside its traditional spectrum. "We have linecards that deliver our ADSL+ solution," he says. "In that chipset you can do enhanced spectrum ADSL2 implementation. In doing that it's a matter of a software change for us. We have the ability to do it today."

Other Video over DSL News

• Next Level Communications last month unveiled new equipment called the Broadband Services Access Multiplexer-Single Shelf Enclosure (BSAM-SSE), which helps telcos deliver digital TV and high-speed Internet. The BSAM-SSE can be placed on top of existing networks in remote cabinets used to deliver local phone service in suburban neighborhoods. Delivery of these types of broadband services was restricted to customers served with equipment in a central office -- greatly reducing its reach. Manitoba Telecom Services will be one of the first telcos to deploy the BSAM-SSE. The product will contribute to the rollout of its large-scale deployment of the Next Level Full Service Access Platform in Winnipeg.

• Net to Net Technologies recently introduced a new microDSLAM with 12 integrated ADSL ports. Available now, the product sells for about $5,995.

• Net to Net Technologies also tells xchange it is developing new video over DSL products that use loop bonding to deliver 20mbps downstream over two pairs at 10,000 feet. "This gives you VDSL rates at ADSL distance," says Matthew Byrd, vice president of marketing at Net to Net Technologies Inc. He adds the solution also will support POTS over both lines.

• mPhase Technologies Inc. is teaming with Lucent Technologies Inc. to deliver a VDSL solution. The combined Lucent-mPhase solution has three key elements: mPhase's digital set-top box which was recently refined by Lucent Technologies' Bell Labs; Lucent's Stinger DSL Access Concentrator as the transport mechanism; and mPhase's Traverser Broadcast Television Switch, which provides video networking intelligence to enable video services over a DSL infrastructure. A prototype will be available by mid-year.

• Tut Systems, which acquired VideoTele.com, in February made the first big announcement since the companies joined forces in November. The M2-400 is a new video edge device (a codex with satellite mux/demux). The company has had a product called the M2 series on the market for about five years. That product was ATM-based; the new M2-400 is IP-based. The product will be generally available this month.

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