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Long-Range, High-Speed Gfast Is Coming – BT

Iain Morris
10/21/2015
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LONDON -- Broadband World Forum -- Gfast equipment suppliers are making swift progress on developing the distribution point units and chipsets that will allow BT to deploy Gfast from street cabinets and realize its broadband network upgrade ambitions, according to Trevor Linney, the UK operator's head of access network research.

A technology that boosts the capability of last-mile copper connections, Gfast is integral to BT Group plc (NYSE: BT; London: BTA)'s long-term broadband plans, the operator having set a target of providing Gfast-based 300-500Mbit/s services to 10 million UK premises by 2020. (See BT Outlines Conditional Gigabit Vision for UK and BT Puts G.fast at Heart of Ultra-Fast Broadband Plans.)

Because it uses much higher frequencies to increase connection speeds, Gfast unfortunately loses its effectiveness over longer distances and is generally being considered where operators have extended fiber networks as far as local distribution points close to customer homes (within 100 meters). (See Copper Soldiers On: Broadband Special Report Part 1 and G.fast: The Dawn of Gigabit Copper?.)

BT, however, has previously indicated that it would be uneconomical to equip all 4 million of its UK distribution points with the necessary electronics. Its aim all along has been to deploy Gfast from many of its 90,000 street cabinets.

Until earlier this year that looked like a pipe dream, but BT's belief that Gfast can eventually meet its future needs has been growing. (See BT Gets G.fast Confidence Boost From Trials.)

To address what Linney calls BT's "ultimate use case," the operator needs vendors to produce much larger distribution point units that come with as many as 96 ports, instead of the four, eight or 16 originally envisaged and designed.

But Linney has been encouraged by his recent observations. "To go from a 16-port unit to a 96-port unit would have been quite scary to the industry a few years ago, but we now see that functionality being added to roadmaps," he said at the Broadband World Forum (BBWF) in London this week.

BT's goal is to drive the effective reach of Gfast technology to around 300 meters. "That is important because the typical distance between a cabinet and a customer home is between 300 meters and 350 meters in the UK, depending on where you are," said Linney.

Since 2008, Openreach , BT's access networks division, has been deploying additional fiber, power and electronics infrastructure at tens of thousands of its cabinet locations and those investments should help the operator to reduce the cost and time it takes to roll out Gfast technology.

Besides sounding a bullish note on distribution point units, Linney also expressed confidence about developments in the Gfast chipset market.

"We're working through international standards to improve Gfast so that it operates at higher speeds on longer copper loops," he said. "We are confident the hardware we need will be ready."


The rollout of gigabit broadband access networks is spreading. Find out what's happening where in our dedicated Gigabit Cities content channel here on Light Reading.


Demonstrating Gfast at BT's BBWF stand, Linney said there were a number of other reasons behind BT's decision to commit to the emerging technology.

The initial standard extends the frequency range over which broadband signals are carried to 106MHz, meaning Gfast can already support "hundreds of megabits per second" in ideal circumstances.

Moreover, the use of spectrum guard bands will allow BT to deploy Gfast without causing any disruption to existing VDSL services. "It's ready to go into the network without requiring customers to upgrade their modems or change their CPEs unless they wish to move to the new service," said Linney.

Speaking during a separate presentation at BBWF, Neil McCrae, BT's chief network architect, also indicated that New IP technologies such as SDN and NFV -- while currently focused on the enterprise segment of the market -- could in future support the rollout of Gfast to UK homes.

"There is a model we've developed with the Broadband Forum [a broadband specifications group] that we will deploy with broadband services," he told conference attendees. "As we move through technology generations that will make it easier to migrate customers and move them around." (See What the Broadband Forum Did Next.)

From the very outset, Gfast rollout will also incorporate technologies for improving the customer experience that BT has gradually been introducing into its VDSL deployment. That includes vectoring, which boosts connection speeds by reducing the crosstalk or interference between the different lines in a telephony cable. (See Vectoring: Some Va-Va-Voom for VDSL.)

XG.FAST trials
Keen to highlight the full potential of copper, BT has also announced that during trials of an experimental technology called XG.FAST -- carried out with France's Alcatel-Lucent (NYSE: ALU) -- it was able to deliver more than 5 Gbit/s over copper loops of 35 meters and speeds of around 1.8 Gbit/s at distances of approximately 100 meters.

"The delivery of 5 Gbit/s over 35 meters, which coincidentally is the typical distance of our final drop, just shows the potential of copper to deliver higher speeds," said Linney. "It's a signpost that copper has more to give."

Responding to questions from Light Reading, Linney said that BT does not currently have any commercial plans to use XG.FAST and indicated the technology would not help BT to provide ultra-fast broadband services over longer distances.

"Given that it's a 500MHz system, I don't think it will be going too far away from the fiber," he said.

Light Reading has also learned the chipset being used in the 5Gbit/s trial is not from a commercial supplier but is an in-house FPGA (field programmable gate array) prototype from Bell Labs , the R&D arm of Alcatel-Lucent.

Lab testing of XG.FAST has been carried out at BT's Adastral Park research facility in the UK and Alcatel-Lucent's labs in Antwerp, Belgium.

— Iain Morris, Circle me on Google+ Follow me on TwitterVisit my LinkedIn profile, News Editor, Light Reading

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