What is G.fast Technology: Features and Specifications

G.fast is a broadband access technology designed to deliver gigabit speed internet services over existing copper telephone lines. By utilizing higher frequency bands and advanced signal processing techniques, G.fast provides fiber like performance while reducing deployment costs and accelerating high speed broadband availability. This page explains G.fast technology basics, comparison of G.fast with VDSL.

G.fast is a technology designed to coexist with VDSL2, adding enhanced capabilities for high speed data communication over digital subscriber lines. It is primarily intended for local loops shorter than 500 meters. The specifications for G.fast are outlined in ITU-T G.9700 and ITU-T G.9701.

G.fast Technology Features

Here are some key features of G.fast technology:

• Speed: Offers speeds ranging from 150 Mbps to 1 Gbps, depending on the loop length.
• TDD Duplexing: Employs Time Division Duplexing (TDD), where both downstream (DS) and upstream (US) communications utilize the same frequency band but different time intervals for transmission. It supports low-power states, and the DS/US ratio can be easily adjusted.
• Bandwidth: Supports a bandwidth of up to 100 MHz.
• DMT Modulation: Uses Discrete Multi-Tone (DMT) modulation with 2048 subcarriers, a subcarrier spacing of 51.75 KHz, and allocates 12 bits per subcarrier.
• PHY Layer Retransmission: The Physical (PHY) layer supports retransmission, improving resilience against impulse noise while maintaining low latency.
• Vectoring: Supports vectoring, which helps to cancel far-end crosstalk.
• Forward Error Correction (FEC): Supports FEC with trellis coding and Reed-Solomon (RS) coding, as defined in G.993.2 VDSL2, along with retransmission block interleaving as defined in G.998.4.
• Network Time Transport: Provides transport of network time and time of the day.
• Loop Length: Designed to operate over loop lengths of 250 meters using a 24 AWG (American Wire Gauge) pair of wires.
• Broadband Forum Architectures: Supports TR-156 and TR-167 broadband forum architectures.