The speed can be reached at distances of up to 70 metres, which would be useful for the new NBN fibre to the node model. But it's still a prototype. Bell Labs says the technology demonstrates how existing copper access networks can be used to deliver 1Gbps symmetrical broadband access services.
Marcus Weldon, president of Bell Labs, said that achieving 1 Gbps symmetrical services – where bandwidth can be split to provide simultaneous upload and download speeds of 1 Gbps – is a major breakthrough for copper broadband.
“It will enable operators to provide Internet connection speeds that are indistinguishable from fibre-to-the-home services, a major business benefit in locations where it is not physically, economically or aesthetically viable to lay new fibre cables all the way into residences. Instead, fibre can be brought to the kerbside, wall or basement of a building and the existing copper network used for the final few metres.”
The Bell Labs tests used a prototype technology called XG-FAST, an extension of the G.fast technology standard currently being finalised by the ITU. When it becomes commercially available in 2015, G.fast will use a frequency range for data transmission of 106 MHz, giving broadband speeds up to 500 Mbps over a distance of 100 metres.
In contrast, Weldon said XG-FAST uses an increased frequency range up to 500 MHz to achieve higher speeds but over shorter distances. Bell Labs achieved 1 Gbps symmetrical over 70 meters on a single copper pair. 10 Gbps was achieved over a distance of 30 meters by using two pairs of lines (a technique known as ‘bonding’). Both tests used standard copper cable provided by an unnamed European operator.
“Our constant aim is to push the limits of what is possible, with breakthroughs that are ten times better than are possible today,” said Weldon. “Our demonstration of 10 Gbps over copper is a prime example: by pushing broadband technology to its limits, operators can determine how they could deliver gigabit services over their existing networks, ensuring the availability of ultra-broadband access as widely and as economically as possible.”
The primary factors influencing broadband speeds over copper are:
- Distance: the longer the copper connection between the access node and the customer’s telephone socket, the slower the broadband speed. This is dictated by attenuation.
- Frequency: the wider the frequency range, the faster the broadband speed that can be achieved. The Shannon Limit dictates the maximum possible speed for a given medium and frequency spectrum.
- Higher frequencies attenuate more quickly than lower frequencies, meaning there are diminishing returns in speed as the frequency range increases.
During testing, Bell Labs showed that XG-FAST technology can deliver 1 Gbps symmetrical services over 70 metres). This was achieved using a frequency range of 350 MHz. Signals at higher frequencies were completely attenuated after 70 metres. In practical situations, other significant factors that can influence actual speeds (not taken into account during these tests but which have been studied extensively elsewhere) include the quality and thickness of the copper cable and cross-talk between adjacent cables (which can be removed by vectoring).