G.fast is a more promising technology than originally expected, said BT Wholesale executive Colin Bannon at the Big Telecom Event in Chicago yesterday.
Manufacturers have targeted G.fast to support speeds of about 500 Mbps over copper phone wiring over a distance of about 100 meters. But Bannon said BT has been testing the technology in the laboratory and has been able to support speeds up to 1 Gbps over distances of 350 meters (approximately 1,100 feet). The company also has done small field trials of the technology. Bannon also noted that BT expects to see enhanced performance from G.fast after manufacturers implement modifications to their products that the carrier has recommended.
“I think we’re onto a winner here,” said Bannon in a presentation to BTE attendees.
The 350-meter distance is important because BT recently modernized its infrastructure to include cabinets at that distance from individual homes as part of a big push to boost broadband speeds and availability across the United Kingdom. The company has been pushing fiber deeper into its network to support higher broadband speeds for end users, but was only looking at G.fast for customers who were closer to the fiber endpoint than 350 meters.
“A technology we were planning to look at for four million sites [is] potentially workable over longer distances,” said Bannon. G.fast, he said, is “supremely promising not only for short range but for those cabinets we just spent three billion on.”
Within the next 10 years, Bannon anticipates that BT might use G.fast to support plans to make broadband speeds up to 500 Mbps available for most of the U.K. and to also support a premium offering of 1 Gbps.
G.fast Technology Tweaks
The product modifications that BT has requested from G.fast manufacturers include:
- Enable higher bits per tone (i.e. 15 vs. 12)
- Increase the transmit power (i.e. 8dBm)
- Increase the vectoring group sizes (>= 96 ports)
- Optimize the frequency usage with VDSL
- Lower noise floors (i.e. <-150dBM/Hz vs. 135 or 140)
BT is planning several field trials of G.fast for this summer including bringing service to 4,000 users in two locations. The company also has deployed the technology to 100 multi-dwelling units.
Bannon noted that in BT’s field trials, customers have experienced broadband speeds of up to 700 Mbps over distances of 50 meters and speeds of 500 Mbps over distances of 150 meters.
And after manufacturers make the modifications BT has requested “it’s going to get a lot better,” Bannon said.
I'm wondering about the "up to 1 Gbps over distances of 350 m" statement. Even for a lab value, that's 4-5 times the best rates I've seen quoted at similar distances. Unless they are bonding several pairs, and boosting the transmit PSD well beyond the standard, I'm skeptical. Has anyone seen anything similar, or know what the conditions were to achieve such results?
G.fast, as specified today, clearly has the ability today to meet the telco’s requirements of 350 meters – but not at 1Gbps over that distance. We believe this might have been a misunderstanding by the reporter. Now the article does point out that BT would like “tweaks.” These changes would need to be reflected in amendments to the standard, but if they were implemented, BT would be able to achieve their quoted target of 500Mbps — all without bonding. With bonding (which is possible with G.fast), the potential is obviously greater.
My understanding is that achieving 1 Gbps over 350 meters using G.fast does indeed require tweaks. BT experimented with various tweaks to boost the technology's performance, such as those summarized in the bullets.
Thanks for reading.
Joan, thanks for the clarification of understanding. It would be helpful to further understand if:
1.The speeds claimed by BT are bi-directional or unidirectional;
2.Performance results from BT field trials were consistent with the lab results;
3.BT believes potential interference with and from other xDSL services can be avoided in production;
4.The stability of the service speed can be provided over time and subject to changing environmental and electrical conditions; and
5.Bonding is needed to achieve the 1Gbps speed.
K/R
David