In 2016, G.fast looked very promising.
Thousands worked at developing and deploying.
It wasn't enough.
Most carriers are investing
in fiber or 5G instead.
Dark Blue: Firm commitments from incumbent: BT (10M), Belgacom, Australian NBN, Swisscom, Austria, Bezeq Israel, Chunghwa Taiwan, Telus Canada, Telekom South Africa, SK Korea, (U.S.) AT&T, Century, Frontier, Windstream, Belgium, Omantel
Mid Blue: Smaller carriers in Germany, Norway, Finland, Japan
- Published: 22 December 2014 22 December 2014
- Vplus delivers speeds exceeding 300Mbps on a single copper pair
- Vplus offers unmatched throughput, density and cost on 200-500m copper loops
- Vplus is a simple extension of existing standard VDSL2 vectoring technology
Vplus is a perfect match for operators who need to deliver the highest possible speeds in a cost-effective way on medium-length loops. Vplus is a new technology that
- Delivers aggregate speeds of 200Mbps and more over traditional copper telephone lines at distances up to 400 meters, and 300Mbps on loops shorter than 200m
- Extends the frequency range used by VDSL2 17a vectoring to 30MHz to achieve these higher speeds
- Can be mixed with existing VDSL2 17a deployments to fill the gap between VDSL2 vectoring (100Mbps aggregate at 700m) and G.fast (500Mbps+ aggregate at 100m)
- Offers higher speeds (up to double) compared to VDSL2 on loops shorter than 500m
- Offers longer reach (higher bit rates beyond 200m) and higher density (100-200 subscribers) compared to G.fast
- Lowers operator costs compared to G.fast
VPLUS FILLS THE GAP BETWEEN VDSL2 VECTORING AND G.FAST
Figure 1 illustrates the typical performances you can expect from VDSL2 vectoring, G.fast, and Vplus.
Aggregate bit rates (upstream + downstream) are used for a fair comparison between technologies. G.fast performance is based on the ITU-T G.9701 standard (approval of which is expected in December 2014), i.e., using up to 106MHz of spectrum, and excluding VDSL2 (17a) spectrum to illustrate a mixed technology deployment.
In terms of bit rate, Vplus fills the gap between VDSL2 vectoring and G.fast. At loop lengths between 200 and 400 meters, Vplus delivers 200+Mbps and outperforms both VDSL2 vectoring and G.fast.
At shorter distances (less than 200m) Vplus does not match G.fast’s speeds, but still delivers up to 300Mbps. So even on short loops, Vplus makes a strong case for operators who need to deliver up to 300Mbps.
On longer loops, Vplus falls back to VDSL2 17a vectoring performance.
HITTING THE TARGET
As a general rule for FTTx, the deployment cost per subscriber and bit rates increase as the “x” moves closer to the end-user. As seen in Figure 2, each xDSL technology has a “sweet spot” area in which it performs best. Choosing the right technology to hit the cost, density and bit rate targets is the goal.
G.fast uses a very wide frequency range, up to 106MHz (to be compared with 17MHz for VDSL2 17a) to deliver 100s of Mbps (up to 1Gbps). This very wide spectrum and the associated very high bit rates require much more processing resources for the transceiver and vectoring functionality than VDSL2, limiting the achievable density of a G.fast design.
At the same time, these high frequencies are only effective over very short distances (typically 250 meters or less). Consequently, G.fast nodes will have a very low port density – typically 16 subscribers or less per system – and will get deployed very close to the home. This results in a high CAPEX cost per user. On the other hand, G.fast will enable a faster adoption of FTTH services, avoiding the need to rewire every front yard and multi-dwelling unit.
In contrast, existing VDSL2 17a vectoring is optimized in terms of bit rate, density and cost for FTTN deployments with loops in the range of 500m to 1000 meters. Since VDSL2 17a is widely deployed today, it offers a fast and cost effective upgrade path to 100+Mbps with vectoring.
Vplus, with its 30MHz spectrum, supports both longer loop lengths (200Mbps over 400 meters) and denser solutions (up to 200 subscribers) compared to G.fast. This makes Vplus the best solution for high-speed FTTN/FTTcurb deployment over medium loop lengths.
In fact, Vplus reach is a very good match for many existing FTTN deployments, and can provide a quick and easy upgrade path for operators that are already deploying VDSL2.
COMPATIBILITY WITH EXISTING VDSL2 VECTORING DEPLOYMENTS
Using frequencies up to 30MHz for VDSL2 is of course not new. That is exactly what the VDSL2 30a standard profile does. However, the 30a tone spacing is different from the 17a tone spacing preventing cancellation of crosstalk between 17a and 30a lines. This makes upgrades of the existing 17a deployments to 30a unattractive as it would require a full swap of the VDSL2 CPE installed base.
Figure 3. VPLUS allows mixed vectoring with VDSL2 17A
Vplus overcomes this limitation by using the same tone spacing as 17a. This allows vectoring across Vplus and 17a lines, and thus mixed deployments and a smooth introduction of Vplus. Since only tone spacing changes, existing 30a band plans can be reused. Alcatel-Lucent has brought Vplus to the ITU for adoption as a straight forward amendment of the VDSL2 standard.