XG-FAST, a potential future development of the technology, is in the early stages of lab testing, but has exceeded expectations in trials at Adastral Park, BT’s global research and development campus in Suffolk, and Alcatel-Lucent’s labs in Antwerp.
It delivered aggregate speeds of 5.6Gbps over 35 metres of BT cable, a record for full-duplex data transmission over a standard single BT line at this distance. The technology also performed well over longer distances, with aggregate speeds of 1.8Gbps over 100 metres; a significant result, as most UK homes are within this distance of their local distribution point, be that a pole or footway box. (below, full duplex excerpt from an article by Jochen Maes and team.)
At the start of the G.fast work, they investigated the possibility of sending data both upstream and down in the same frequency. It wasn't included then. There are trade-offs: complexity, reach, robustness.