G.fast: A Powerful Weapon for Telcos

Carl Weinschenk

Approval of G.fast digital subscriber line (DSL) technology is an early Christmas present for the telephone industry. It potentially offers tremendous advantages for these companies, which are facing ever-tougher competition from cable MSOs, Google Fiber – and other independent providers – and wireless operators.

G.fast gives further life to the massive amount of legacy copper cabling that dominates the last mile of telephone networks. The standard, which received its final approval from the International Telecommunication Union (ITU) earlier this month, increases capacity and flexibility by radically expanding the spectrum into which data is packed to 106 MHz and using a more pliable modulation scheme.

G.fast is built for speed, not distance. The standard is operational at 400 meters, experts say, but is clearly designed to provide the most benefits – and therefore a justifiable ROI – at loop lengths of about 250 meters.

Now that the standard is established, two related processes start. Interoperability testing, which is held in a series of colloquially named “plug-fests,” will ensure that equipment produced by different chipset and consumer premise equipment manufacturers works together. The first is scheduled next month, with three others expected during the first half of 2015.

The second is a certification process, which is run under the auspices of the Broadband Forum. There are no formalized times for the “cert testing.”

Both the plugfests and certification program are being run by the University of New Hampshire InterOperability Lab (UNH-IOL). Field trials also are expected in 2015. Michael Weissman, the vice president of marketing for chip maker Sckipio, said that he expects commercial hardware deployments during the second half of the year.

A Faster Standard

The increased capacity more or less eliminates copper as the weak link in hybrid fiber/copper networks. G.fast even helps in scenarios that are dominated by fiber: Fiber-to-the-premise (FTTP) builds invariably have pockets of subscribers in difficult or expensive to reach areas. G.fast will be used in these scenarios to ensure that no subscribers are left behind. “[G.fast] will accelerate fiber-to-the-home because it alleviates problems with some of the households,” said Keith Russell, the senior product marketing manager for Alcatel-Lucent.

G.fast also is more easily managed. Early versions of DSL could be self-installed by telcos’ subscribers. The industry got away from that as the copper loops got longer. G.fast’s shorter loop lengths mean that self-installs again become possible.

As if all that isn’t enough, G.fast also transfers a key cost to subscribers: The short loop facilitates reverse power feed (RPF). That’s a fancy way of saying that homeowners supply (and foot the bill for) running the demarcation points between the fiber and copper infrastructure. The overall power consumption – regardless of who is footing the bill – also is reduced, said Les Brown, the associate rapporteur for G.fast at the ITU-T.

Data Networking

A Reimagining of DSL

All of these benefits are based on a fundamentally different approach to the challenge of providing high levels of data over copper. Previous versions of DSL employed modulation techniques based on code division multiple access (CDMA). In such scenarios, data flows simultaneously in both directions. G.fast divides channels into 50 MHz wide blocks and uses a technique – discrete multitone modulation – that is based on time division multiplexing (TDM). In TDM, traffic flows in each direction sequentially. The upstream and then the downstream have the entire digital platform for minute amounts of time. This is far less complex and provides a tremendous flexibility and control. Traffic can flow symmetrically or asymmetrically – in equal or different quantities – as the operators sees fit.

This approach also makes it more likely that the treacherous copper in the home can be traversed. “You have all the different jacks in each room and all those things,” said Lincoln Lavoie, the senior engineer of Broadband Technologies at UNH-IOL. “It is not tuned for high speed communications. G.fast is very adaptable in how it works and will fund the optimal way…It will avoid bands that are funky or dirty.”

The transition to G.fast is a big deal, but not without challenges. Kourosh Amiri, the vice president of worldwide marketing for Ikanos, says that the three main concerns – which will only be assessed after field trials – likely will be the implementation of RPF, whether G.fast will be able to support previously deployed VDSL technology, and whether the real costs of installation are manageable. “Nobody can tell the success rate until the carrier field trials, most of which are scheduled in 2015,” he said.

Those field trials also will provide service providers with an idea of how to best extend their networks. Some may have fiber close enough to the premises they want to serve to easily transition to G.fast. Others may have dark fiber available to come within the 250 meters, Weissman said. In still others, the promise of G.fast may lead to a rebuild decision.

Weissman said that the low-hanging fruit will be in urban areas with a high density of MDUs. In such scenarios, fiber likely is geographically close. But actually reaching subscribers – some of whom live in apartments hundreds of feet from the fiber cabinet in the basement -- is difficult and expensive. “The place of highest urgency for G.fast is high density environments,” he said. “Now you can implement G.fast with very little investment.”

The bottom line is that the telephone industry has a lot riding on G.fast – and that the future will start taking shape with next year’s field trials. “I think it’s a significant change, quite significant,” Brown said.

Carl Weinschenk covers telecom for IT Business Edge. He writes about wireless technology, disaster recovery/business continuity, cellular services, the Internet of Things, machine-to-machine communications and other emerging technologies and platforms. He also covers net neutrality and related regulatory issues. Weinschenk has written about the phone companies, cable operators and related companies for decades and is senior editor of Broadband Technology Report. He can be reached at cweinsch@optonline.net and via twitter at @DailyMusicBrk.

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