What Is G. fast?
The name G.fast is an acronym for Fast Acess to Subscriber terminals. The letter G, stands for the ITU-T G series of recommendations. G. fast is a digital subscriber line (DSL) protocol standard for local loops shorter than 500 m, with performance targets between 100 Mbit/s and 1 Gbit/s, depending on the loop length.
In G.fast, data is modulated using descrete multi-tone (DMT) modulation, as in VDSL2 and most ADSL variants. G.fast modulates up to 12 bit per DMT frequency carrier, reduced from 15 in VDSL2 for complexity reasons.
What Is VDSL?
VDSL is an acronym for very high speed digital subscriber line. It is a digital subscriber line (DSL) technology providing data transmission at a faster rate when compared to asymmetric digital subscriber line (ADSL).
VDSL offers speeds of up to 52 Mbit/s downstream and 16 Mbit/s upstream, over a single flat unteisted or twisted pair of copper wires using the frequency band from 25 kHz to 12 MHz. These rates mean that VDSL is capable f supporting applications such as high-definition television as well as telephone services (voice over IP) and general internet access, over a single connection. VDSL is deployed over existing wiring used for analogue telephone service and lower speed DSL connections.
Also Read: Difference Between SDMA, TDMA, FDMA And CDMA
Difference Between VDSL And G.fast In Tabular Form
| BASIS OF COMPARISON | VDSL | G. FAST |
| Meaning | Very high Bit Rate Digital Subscriber Line. | Fast Access To Subscriber Line. |
| Frequency | Up to 30MHz | 2 to 106 MHz 2 to 212 MHz planned for future profiles. |
| Maximum Data Rate | 100 Mbps in both upstream and downstream (VDSL 2). | 1Gbps over distance of 70 meter, 800 Mbps over distance of 100 meters. 500 Mbps over old shielded type of cable (distance of 100 meters). |
| Modulation Type | DMT (Discrete multi-tone modulation) e.g OFDM (Orthogonal Frequency Division Multiplexing). | Frequency Division Multiplexing (FDM). |
| Duplexing Method | FDD (Frequency Division Duplex). | TDD (Time Division Duplex). |
| OFDM | Approximately 250 µSec (in 17MHz profile). | Approximately 20µSec |
| Vectoring Method | Using ITU-T G.993.5 | Supported along with adaptations required for high frequency. |
| Transmit Power | It depends on profile, 14.5 dBm. | 4 dBm |
| FEC Type | RS Coding (Reed Solomon coding), trellis coding. | RS Coding (Reed Solomon coding), trellis coding. |
| Bits Per DMT Frequency 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 |
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