HDSL2 issues move toward resolution

Vendors working toward the HDSL2 standard for single-pair high bit-rate digital subscriber line seem determined to avoid a winter of discontent. With seven weeks until the next standards committee meeting, the major vendors last week marshalled a tide of goodwill to drown out the earlier buzz of a technology war in the making.

ADC Telecommunications and Level One Communications, partners in HDSL development, updated industry watchers on HDSL2's development and said vendors are close to agreeing on a line code scheme to meet the spectral compatibility requirements for the standard.

Other HDSL vendors, including Adtran, Siemens, PairGain, Rockwell, Globespan and Paradyne, confirmed the cooperation.

"There's no big line code fight going on. This is the way the process is supposed to work," said George Zimmerman, chief scientist at PairGain.

Spectral compatibility of HDSL2's line code with existing services is the only unresolved issue. Adtran and Siemens have supported pulse amplitude modulation (PAM), while PairGain, ADC, Level One and Rockwell backed a variation on PAM called overlapped PAM transmission with interlocking spectra. The platform basis for both line codes is Adtran's partially overlapped echo transmission technology.

"You can use any modulation scheme on a line code. We will work to make sure it meets HDSL's spectral compatibility requirements," said Keith Atwell, HDSL product manager at Adtran.

In fact, HDSL2 planners have committed themselves, with some carrier influence, to reaching a consensus on the most spectrally compatible line code at the next T1/E1.4 meeting Dec. 8-12 in Sacramento.

"There was a divergence in line code interests that made problems for the ADSL standard. We want to work together to avoid that," said Mike Rude, senior project engineer at ADC and the lead editor for the HDSL2 standard.

"Vendors are less cantankerous about this standard," added John Griffin, director of marketing at ADC.

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