Triple-Play Broadband By DSL A No Go? CO Chip Set Says Not So

The broadband triple play via DSL isn't practical, but it is possible. That said, the Pharos chip set from Centillium Communications streamlines ADSL performance to bring voice, video, and data over the existing plain-old-telephone-service (POTS) structure. Designers can use it to upgrade most DSL central-office (CO) equipment.

While current ADSL rates in the U.S. theoretically extend to 6 Mbits/s, rarely does the average consumer get more than the typical 1.5 Mbits/s. The Pharos chip set implements the Annex A ITU-T standard, which covers DSL over POTS, including ADSL2, ADSL2+, and the forthcoming ADSL2++ (see the figure). It also supports Annex B standards for ISDN in Europe and Annex C ISDN in Japan.

ADSL2 provides up to 12 Mbits/s downstream and 1.2 Mbits/s upstream. ADSL2+ supplies up to 24 Mbits/s downstream and 1.2 Mbits/s upstream. Not yet a full standard, ADSL2++ provides 50 and 3.75 Mbits/s, respectively. Ranges to 8 km are possible based on the cabling.

Designed for CO DSLAM line cards, the set consists of a single 12-port digital processor chip and a two-port analog front-end chip. The front-end chip integrates line drivers and other components, such as tone and metering filters, that reduce the total component count. Pharos also offers superior characteristics that enable quality-of-service like dual latency, dynamic rate repartitioning, and seamless rate adaptation.

Service providers can use the set's patented dual- and single-ended line-testing circuits to perform remote diagnostics, troubleshooting, and provisioning. This virtually eliminates maintenance and truck-roll costs.

With an available PC, carriers can manage, test, and evaluate signal-to-noise ratio and other critical line conditions. Low power consumption and on-chip power management will permit more ports per DSLAM while also lowering overall costs.

The Pharos chip set is available now in engineering quantities. Customer samples will be available near year's end. Contact Centillium for preliminary pricing.