Ratified by the International Telecommunication Union (ITU) in February, ADSL2+ boosts the speed and range of existing ADSL lines, with on-paper potential for 25 Mbit/s at distances of about 6,000 feet -- real performance varies depending on the surrounding environment [ed. note: and dealer preparation charges, local taxes, and licensing fees]. The technology would also extend the reach of 384-kbit/s ADSL service to about 16,000 feet.
Better speed and reach always sound good, but the real target is video. "With enough video compression, you can have up to three video streams running on ADSL2+," says Angelo Stephano, vice president of marketing for GlobespanVirata Inc. (Nasdaq: GSPN).
Video would give ADSL an entry in the fabled (and by now clichéd) "triple play" of voice, data, and video services (see Telcos Tackle Triple Play ). More important, it would be a counterbalance to cable, which has gotten its own triple play going by offering voice services.
"We're seeing genuine interest [in ADSL2+] because the cable guys are getting penetration in voice," says David Benini, DSL marketing manager for Aware Inc., a company that develops technology for chip makers.
Very high speed DSL (VDSL) was supposed to help boost DSL video, but ADSL has been pumped up enough to become a viable alternative.
"It will take time for VDSL to be installed and deployed, because it requires a lot of different infrastructure," Stephano says. VDSL isn't completely ratified, due in part to a tiff over line-code schemes (see High Noon Arrives in VDSL Battle). Moreover, the VDSL standard isn't going to support the long reaches that ADSL can hit, and VDSL equipment will be relatively expensive for some time.
Here's a rundown of ADSL's recent makeover:
- ADSL2: Not as racy as it might sound, this provides some power savings and performance enhancements, and a bit of speed. Maximum downstream speed is increased to 10 or 12 Mbit/s, up from 8 Mbit/s. Ratified by the ITU last October.
- ADSL2+: Doubles the available spectrum for ADSL, allowing downstream transmission to use frequencies up to 2.2 MHz. The result is the 25-Mbit/s speed mentioned above.
- ReachExtended ADSL: Also called RE-ADSL or ADSL Annex L, it allows ADSL to travel more than 20,000 feet at 384 kbit/s. DSL speeds decline the farther you are from the central office, so previous 20,000-foot service would deliver speeds of just about zero.
RE-ADSL is on the verge of ratification; the ITU has frozen the spec and is likely to complete it in October, Benini says.
The kicker is that all three functions can run on the same chip. Board makers only have to produce one line card, and the equipment operators can decide which combination of these new powers to wield.
For North America, equipment using ADSL2 and ADSL2+ should arrive towards the end of the year, but some of the technology is already being deployed in other parts of the world.
For example, chips from Centillium Communications Inc. (Nasdaq: CTLM) are already being used for 12-Mbit/s service in Japan, "and we're just about to roll the 24-Mbit/s services," says Alex Aali, senior marketing manager for Centillium. "Japan has been more aggressive in rolling out high-speed services than the rest of the world, so some of these technologies will be appearing there first."
There's no ADSL3 on the horizon yet, Benini says. But the next step might be to increase the density of DSL lines in a bundle. He says researchers at Stanford University are working on Dynamic Spectral Management, "which allows you to dynamically manage the different lines in a bundle, because they crosstalk with each other, and they interfere with each other."
Some vendors are also considering quadrupling the downstream spectrum to produce 50-Mbit/s service, sort of an "ADSL2-plus-plus," Aali says.
— Craig Matsumoto, Senior Editor, Light Reading