Zhone Technologies unveiled new IP DSLAMs this week in accordance with the vendor’s strategy of using two technologies to help carriers offer advanced services over their current copper infrastructure: VDSL2 for short loops -- under 5,000 feet -- and bonded ADSL2+ for longer loops.

This week Zhone introduced the Bitstorm HP, a 24-port one-rack-unit VDSL2 IP DSLAM designed to deliver 100 Mb/s symmetrically, and the Bitstorm RP, a 48-port ADSL2+ device that enables two bonded copper pairs to carry up to 25 Mb/s over 10,000 feet.

“The basic returns [on VDSL] beyond 5,000 feet are not quite there,” said Uttam Singh, Zhone’s director of vertical solutions. “The VDSL2 specs say [it reaches] up to 12,000 feet, but the rates are just not there.”

Part of what allows Zhone’s gear to deliver 100-Mb/s symmetrical speeds is that it operates at a higher frequency, 30 MHz, than other forms of DSL. The chips, based on Discrete Multitone (DMT) modulation, also allow for more customization of how upstream and downstream bandwidth is used, maximizing efficiency to yield greater throughput. In some cases, carriers can be apprehensive about making these customizations where VDSL lines might sit in the same binder groups as other non-VDSL lines, fearing crosstalk issues. But as more pure-VDSL is deployed by itself in the basements of multidwelling units, carriers can feel more comfortable tweaking up speeds.

“As these boxes move inside the building, they’re a lot more open to customization,” Singh said.

VDSL costs a bit more than other technologies, Singh admits, but in addition to the ample throughput, it also carries other benefits by virtue of being based on Ethernet rather than legacy ATM technology. “It’s all VLAN-centric,” he said. “You’re not spending time doing ATM segmentation for the last few thousand feet. You can carry [quality of service] transparently to the customer premises device.”

Perhaps most importantly, Singh said, VDSL2 is the ideal technology to deliver video over existing copper networks. It can reliably carry three high-definition television signals, along with basic high-speed Internet service, over 2400 feet, or two HD signals over 3500 feet, he said.

Zhone doesn’t yet offer bonded VDSL2, which AT&T has vowed to deploy later this year.