VDSL vs. G.fast: A Detailed Comparison

vdsl
g.fast
dsl
data transmission
networking basics

This article compares VDSL and G.fast, highlighting the key differences between these digital subscriber line (DSL) standards used for data transmission. Let’s dive into the details!

Main Differences Between VDSL and G.fast

The following table summarizes the primary differences between VDSL and G.fast.

SpecificationsVDSLG.fast
Full FormVery High Bit Rate Digital Subscriber LineFast Access to Subscriber Terminals
FrequencyUp to 30 MHz2 to 106 MHz, 2 to 212 MHz planned for future profiles
Maximum Data Rate100 Mbps in both upstream and downstream (VDSL2)1 Gbps over a distance of 70 meters, 800 Mbps over a distance of 100 meters, 500 Mbps over old shielded cable (100 meters)
Modulation TypeDMT (Discrete Multi-Tone Modulation) e.g., OFDMOFDM (Orthogonal Frequency Division Multiplexing)
Number of Subcarriers4K (in a FFT)2K (in 106MHz profile)
Duplexing MethodFDD (Frequency Division Duplex)TDD (Time Division Duplex)
OFDM Symbol TimeApproximately 250 µSec (in 17MHz profile)Approximately 20 µSec
Vectoring MethodUsing ITU-T G.993.5 supported, along with adaptations for high frequencyN/A (implicitly supported)
Transmit PowerIt depends on the profile, typically 14.5 dBm4 dBm
FEC TypeRS Coding (Reed Solomon Coding), trellis codingRS Coding (Reed Solomon Coding), trellis coding
Bits per DMT Carrier15 (in VDSL2)12
Impulse Noise ProtectionAvailable in VDSL2Available
StandardITU-T G.993.2, ITU-T G.993.5ITU-T G.9700, G.9701

Key Takeaways

  • Frequency: G.fast utilizes a significantly higher frequency range than VDSL, allowing for greater bandwidth.
  • Data Rate: Consequently, G.fast offers the potential for much higher data rates, exceeding 1 Gbps in optimal conditions, while VDSL2 is capped at around 100 Mbps.
  • Distance: G.fast’s high data rates are typically achieved over shorter distances compared to VDSL.
  • Duplexing: VDSL employs FDD, while G.fast uses TDD, impacting how upstream and downstream traffic are managed.
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