Alcatel-Lucent (Euronext Paris and NYSE: ALU) says its Bell Labs research group has demonstrated aggregate 10-Gbps transmission across 30 m of copper plant using a prototype variant of the G.fast technology currently the subject of ITU-T standardization. The lab demonstration points to the potential of G.fast and its variants to enable carriers to match fiber to the home (FTTH) speeds using already installed copper cabling.
The G.fast specifications are expected to define a variety of distance/data rate combinations, topping out at the data rate end at 500 Mbps over 100 m. However, the specifications also will leave room for vendors to stretch beyond those figures with proprietary approaches, and most technology developers interested in employing the specifications expect to produce G.fast-based systems that will support at least 1 Gbps downstream (see, for example, "Alcatel-Lucent demos 1-Gbps G.fast with Telekom Austria").
The Bell Labs prototype, dubbed XG-FAST, operates at different frequency ranges than the 106 MHz the specifications will call out. Alcatel-Lucent says that XG-FAST can support an aggregate of 2 Gbps over 70 m at a frequency of 350 MHz on a single copper pair. This “aggregate” is the combination of upstream and downstream data rates; the time-division duplex (TDD) technique G.fast employs enables time slots to be allocated to upstream and downstream traffic to share this total data rate aggregation. So the 2-Gbps aggregate could translate into a symmetrical 1-Gbps service or a service with a faster downstream rate at the expense of a slower upstream rate.
For the aggregate 10-Gbps transmission, Bell Labs combined 500-MHz transmission with bonding of two pairs. Again, this could translate into a symmetrical 5-Gbps service.
However, Alcatel-Lucent points out that Bell Labs researchers obtained both the 2-Gbps and 10-Gbps results in a lab environment, and that real-world performance may not be as robust in all circumstances. The quality, age, and type of copper could affect performance, as could cross-talk from adjacent cables. Vectoring technology could mitigate this last factor, however, as it does with VDSL2.
“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,” offered Federico Guillén, president of Alcatel-Lucent’s Fixed Networks business via a press release. “XG-FAST can help operators accelerate FTTH deployments, taking fiber very close to customers without the major expense and delays associated with entering every home.”
The ITU-T should complete the G.fast specifications this year. Alcatel-Lucent predicts that commercially available products based on the ITU-T specifications should become available next year. The company did not discuss a timeframe for commercialization of the XG-FAST technology.
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