RFVDSL vs. G.fast: A Detailed Comparison
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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.
| Specifications | VDSL | G.fast |
|---|---|---|
| Full Form | Very High Bit Rate Digital Subscriber Line | Fast Access to Subscriber Terminals |
| Frequency | Up to 30 MHz | 2 to 106 MHz, 2 to 212 MHz planned for future profiles |
| Maximum Data Rate | 100 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 Type | DMT (Discrete Multi-Tone Modulation) e.g., OFDM | OFDM (Orthogonal Frequency Division Multiplexing) |
| Number of Subcarriers | 4K (in a FFT) | 2K (in 106MHz profile) |
| Duplexing Method | FDD (Frequency Division Duplex) | TDD (Time Division Duplex) |
| OFDM Symbol Time | Approximately 250 µSec (in 17MHz profile) | Approximately 20 µSec |
| Vectoring Method | Using ITU-T G.993.5 supported, along with adaptations for high frequency | N/A (implicitly supported) |
| Transmit Power | It depends on the profile, typically 14.5 dBm | 4 dBm |
| FEC Type | RS Coding (Reed Solomon Coding), trellis coding | RS Coding (Reed Solomon Coding), trellis coding |
| Bits per DMT Carrier | 15 (in VDSL2) | 12 |
| Impulse Noise Protection | Available in VDSL2 | Available |
| Standard | ITU-T G.993.2, ITU-T G.993.5 | ITU-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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