'First Mile' Ethernet Hits Snags
Participants in the 802.3ah task force had hoped to settle the issue during last week's Institute of Electrical and Electronics Engineers Inc. (IEEE) meetings in Hawaii, but the matter is now slated for a showdown at the group's January meeting, in Vancouver.
Other parts of the 802.3ah standard are proceeding apace. All reports say the fiber optic portions of the group have reached early agreement; and even the copper camp has found some common ground, assigning very-high bit-rate DSL (VDSL) as the technology to support for short-reach links supplying 10 Mbit/s at distances up to 750 m.
Standards for the long-reach connection over copper, however, have hit a stalemate. Most of the chip vendors in attendance would like the standard to declare asymmetric DSL (ADSL) as the technology to use here, but carriers appear to favor G.SHDSL, a version of DSL created within the International Telecommunication Union (ITU) (see First-Mile Ethernet Camps Dig In).
The dispute does not put the entire 802.3ah effort in jeopardy, but it's likely to delay ratification of the standard beyond the September 2003 target date.
Similar disputes arose on the fiber optic side of the standard, but participants simply agreed to allow two options, assigning a different port to each one. That same two-port method should apply on the copper side, says Behrooz Rezvani, CTO of chip maker Ikanos Communications Inc., which is supporting the ADSL side.
"That's the best way to go forward. It allows Ethernet to be available in the network both to business customers and to residences," Rezvani says.
Another wrinkle is that there's a separate war over which modulation scheme to use for Ethernet over VDSL -- quadrature amplitude modulation (QAM) or discrete multitone (DMT) (see Ethernet Over Copper: Now You’re Talking). Rezvani believes the G.SHDSL camp is acting simply to defend QAM.
"This other group wants to win it all -- they want G.SHDSL [at the exclusion of ADSL], essentially. But the industry now could face a problem with that. ADSL is such a pervasive technology. It's doing very well in terms of interoperability and availability," Rezvani says.
Not so fast, say G.SHDSL supporters. According to Dan Carnine, market development manager for chipmaker Metalink Ltd. (Nasdaq: MTLK), his camp is trying to adhere to the spirit of IEEE standards, where there's typically only one physical-layer chip, or PHY, that comes out of a given project -- while the short- and long-reach copper options are bundled together in a single IEEE project authorization request (PAR). Moreover, the only reason 802.3ah includes a long-reach copper option is because SBC Communications Inc. (NYSE: SBC) requested it -- and SBC wants G.SHDSL supported there, Carnine says.
It's debatable whether the IEEE would frown on a two-PHY approach. "It depends on how you interpret certain rules in IEEE," Rezvani says. "Whether they should select only one modulation technology that spans the entire copper spectrum, that's the cause of the problem right now."
In addition, Carnine doubts there's a market for Ethernet over ADSL. His argument goes like this: North American ADSL buildouts are based on ATM, not Ethernet; Europeans can't use the ADSL PHY being suggested because it would encroach on ISDN bands; and Asia isn't interested because 90 percent of the loops there are shorter than 1 km, hence suitable for VDSL.
"There is no demand for an Ethernet-based ADSL. If there were demand, the ADSL vendors would have already developed the technology, and they would be shipping in volume," Carnine says via email.
These kinds of squabbles are common in IEEE standards, as companies try to fit existing technologies into them. The 802.17 standard for Resilient Packet Rings was similarly split before the group settled on a compromise specification. (During the Hawaii meetings, the RPR group managed to complete the latest version of its working-group ballot, a major step towards getting the standard completed.)
For now, the copper issue remains in dispute, with both sides hoping to reach settlement in January. "It all really depends on the mood of everybody at the next meeting," says Rezvani.
— Craig Matsumoto, Senior Editor, Light Reading
Want to know more? The big cheeses of the optical networking industry will be discussing first-mile Ethernet at LightSpeed Europe. Check it out at http://www.lightspeedeurope.com/conference_program.asp.