Bell Labs prototype technology also demonstrates potential for 1 Gbps symmetrical services, paving the way for fibre-speed services where fibre cannot be deployed all the way to the premises
Bell Labs, the research arm of Alcatel-Lucent, has set a new broadband speed record of 10 gigabits-per-second (Gbps) using traditional copper telephone lines and a prototype technology that demonstrates how existing copper access networks can be used to deliver 1Gbps symmetrical ultra-broadband access services.
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 curbside, 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. This is an extension of G.fast technology, a new broadband 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, 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 metres on a single copper pair. 10 Gbps was achieved over a distance of 30 metres by using two pairs of lines (a technique known as “bonding”). Both tests used standard copper cable provided by a European operator.
Marcus Weldon, President of Bell Labs said: “Our constant aim is to push the limits of what is possible to ‘invent the future’, with breakthroughs that are 10 times better than are possible today. 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.”
Commenting on the achievement, Federico Guillén, President of Alcatel-Lucent’s Fixed Networks business said: “The Bell Labs speed record is an amazing achievement, but crucially in addition they have identified a new benchmark for ‘real-world’ applications for ultra-broadband fixed access. XG-FAST can help operators accelerate FTTH deployments, taking fibre very close to customers without the major expense and delays associated with entering every home. By making 1 gigabit symmetrical services over copper a real possibility, Bell Labs is offering the telecommunications industry a new way to ensure no customer is left behind when it comes to ultra-broadband access.”
Technical background information
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 (for the cable being tested). 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).
|Technology||Frequency||Maximum aggregate speed||Maximum Distance|
|VDSL2*||17 MHz||150 Mbps||400 metres|
|G.fast phase 1*||106 MHz||700 Mbps||100 metres|
|G.fast phase 2*||212 MHz||1.25 Gbps||70 metres|
|Bell Labs XG-FAST**||350 MHz||2 Gbps (1 Gbps symmetrical)||70 metres|
|Bell Labs XG-FAST with bonding***||500 MHz||10 Gbps (two pairs)||30 metres|
* Industry standard specifications. G.fast allows for upload and download speeds to be configured by the operator.
** In a laboratory, reproducing real-world conditions of distance and copper quality.
*** Laboratory conditions.