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ITU readies gigabit G.fast standard for copper's last wild ride

FM broadcasters prep 'git offa mah lawn' signs

BT splitter node

The International Telecommunications Union (ITU) has taken the first steps towards standardising G.fast, the next major DSL-based standard which vendors hope will provide a “fibre-like” experience without having to drag the glass all the way into homes.

While it's touted by vendors as a gigabit-over-copper technology, the official ITU line is more conservative. In a video discussing the standard, ITU Rapporteur for Study Group 15 Frank van der Putten says “where ADSL was about a few megabits per second to the end customer, VDSL a few tens of megabits, G.fast will be about a few hundreds of megabits to the end customer.”

The ITU Study Group 15 meeting gave first-stage approval to Recommendation ITU-T G.9700, designed to protect broadcast services such as FM radio from interference caused by G.fast deployments.

That's an important constraint for the new technology. To achieve its impressive performance over even short distances, G.fast needs more than 100 MHz of RF spectrum, compared to the sub-megahertz RF needed by ADSL and the megahertz spectrum used by VDSL variants.

While the 100 MHz-wide profile enables the very high bitrates, it's also what limits G.fast's transmission distance – and there's another problem the standards setters had to solve.

FM radio stations occupy spectrum from around 87 MHz to around 107 MHz – well within that used by G.fast. And, of course, even if they're underground, the copper plant provides a long antenna. That means any emission from the cables is going to destroy FM radio transmissions.

To avoid this, the kit (or the operator) will have to be able to “notch” around frequencies that are in use in a deployment area.

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“A key aspect will also be that G.fast wants to be a self-install technology,” van der Putten adds – by which he means the consumer kit should simply plug into existing comms connections in the home, without the need for operators to install anything new.

“Our intention, our goal is to approve the first version of G.fast, a 100 MHz wide profile, early next year,” he says in the video. That will then pave the way for interoperability testing before chipsets become available and manufacturers get busy on equipment. That would enable kit to ship in 2015.

Interestingly, van der Puttin seems to view G.fast as the last gasp for the copper network, saying in the video that the next step is “probably” fibre to the home. ®

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