Vendors, Researchers Get 'Passive' Aggressive

Carl Weinschenk

Passive optical networks (PONs) are networks in which signals are not amplified after a point that is fairly distant from its destination. The absence of amplifiers and other active devices can make PONs less expensive and more reliable than actively driven networks.

Work is ongoing to further enhance those advantages, especially the lower cost. Light Reading reports on a significant project, albeit one that may not bear fruit for a decade. The GreenTouch consortium, the site reports, is working on a way to reduce the power draw of PON networks by a factor of 1,000. The technology they are developing, called bit-interleaved PON (Bi-PON), focuses on the endpoint where the signals enter the home or business.

The savings is realized by only sending traffic intended for the particular end point. In current systems, all PON traffic is available to every optical network unit (ONU). At that point, the ONU - which often is on the side of a house in a residential system - determines what is needed.

The consortium, which includes Bell Labs and IMEC, proposes using time-division multiplexing (TDM) to assign timeslots to ONUs that request data. Only that data - not the whole load - is sent to the ONU. Light Reading reports that the ONU power draw is reduced from about 2 watts to about 100 milliwatts. The path to actual products won't be quick, though. The Light Reading piece paraphrases Peter Vetter, who is GreenTouch's principal Bi-PON investigator:

Commercialization would be tricky, because the ONUs and the central office need to be talking to each other continually, in a more advanced dialogue than they have today. Any commercial version would be about a decade away, Vetter thinks.

The Enterprise Networking Planet story on the project notes that the consortium is running shorter-term initiatives:

In the interim, there are improvements to PON and ONU deployments that GreenTouch is also working on that provide an enhanced sleep mode that regulates the power based on usage activity. The enhanced sleep mode can work with existing equipment and can potentially be deployed by service providers this year.

GreenTouch isn't the only project aimed at evolving PON architectures. In Europe, the Sardana project - which is described at the Science Daily site as "Scalable advanced ring-based passive dense access network architecture" - focuses on updating the topography of how the signals are trafficked from the source to the end point. Thus, the gains are realized in a significantly different way than in the GreenTouch initiative. It seems logical to think that the two can work together to drive efficiencies even deeper.

Though the Sardana project is closer to realization than the GreenTouch initiative, it still isn't here. Early this month, Mindspeed Technologies released a product that actually is available. The M02150 is described in great detail in the press release. It is, however, an explanation that is best understood by people in the field. The product is described in the release headline as a "complete 10-Gigabit passive optical network physical media device chipset solution."

PONs, at their heart, are simple: The longer and more end points signals that can be sent without amplification, the better off both the carrier and customer are. On top of that rather simple idea, however, rests a tremendous amount of complexity. It is that complexity the vendor community clearly is embracing.

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