Gfast

G.fast is a digital subscriber line (DSL) technology designed to deliver high-speed broadband over existing copper telephone lines for short distances. It is intended for fiber-to-the-distribution-point deployments, where a fiber-fed access node reaches customer premises over the last few hundred meters of copper, providing a bridge between fiber and traditional copper networks.

Its modem technology uses discrete multi-tone (DMT) modulation similar to VDSL and employs techniques such as vectoring to cancel crosstalk between lines. In newer implementations, bonding can combine multiple copper pairs to increase throughput. The standard defines several channel bandwidths, with higher frequency ranges enabling higher data rates.

Hardware and topology: A G.fast modem or gateway at the customer premises connects via a short copper pair to a G.fast-enabled node in a street cabinet or distribution point. Short loop lengths and controlled loading improve performance. The technology is designed to coexist with VDSL2 and can be deployed alongside existing DSL infrastructure.

Standards and profiles: ITU-T has published G.9700 (architecture) and G.9701 (transmission) specifications. Profiles use spectrum up to 106 MHz, with later profiles extending to 212 MHz. Bonding up to multiple pairs and vectoring are supported to boost performance, particularly in dense multi-tenant environments.

Performance and limitations: The achievable speeds depend on loop length and line quality. On the shortest copper runs, peak downstream rates can approach 1 Gbps, with uplink typically lower. On longer loops, practical speeds fall to a fraction of the peak. G.fast is most effective within about 100 meters of copper.