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Vplus gets more out of VDSL2 vectoring

Highlights

  • Vplus delivers speeds exceeding 300Mbps on a single copper pair
  • Vplus offers unmatched throughput, density and cost on 250-550m copper loops
  • Vplus is now standardized by the ITU-T as VDSL2 profile 35b

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 500m, and 300Mbps on loops shorter than 250m
  • Extends the frequency range used by VDSL2 17a to 35MHz to achieve these higher speeds
  • Can be mixed with existing VDSL2 17a deployments to fill the gap between VDSL2 17a vectoring (100Mbps aggregate at 700m) and G.fast (500Mbps+ aggregate at 100m)
  • Offers higher speeds (up to double) compared to VDSL2 17a on loops shorter than 550m
  • Offers longer reach (higher bit rates beyond 250m) and higher density (100-200 subscribers) compared to G.fast
  • Initially introduced by Alcatel-Lucent and now identified as profile 35b by the ITU-T

VPLUS FILLS THE GAP BETWEEN VDSL2 VECTORING AND G.FAST

Figure 1 illustrates the typical performances you can expect from VDSL2 17a 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 standard (G.9701 12/2014) , i.e., using up to 106MHz of spectrum, and excluding VDSL2 17a spectrum to illustrate a mixed technology deployment.

Vplus fills the gap between VDSL2 17a vectoring and G.fast

Figure 1. Vplus fills the gap between VDSL2 17a vectoring and G.fast

In terms of bit rate, Vplus fills the gap between VDSL2 17a vectoring and G.fast. At loop lengths between 250m and 550m. Vplus delivers 200+Mbps up to 500m and outperforms both VDSL2 17a vectoring and G.fast.

At shorter distances (less than 250m) Vplus does not match G.fast’s speeds, but still delivers over 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.

xDSL technology sweet spots

Figure 2. xDSL technology sweet spots

G.fast
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). These high frequencies are only effective over very short distances, typically 250m or less. At the same time, 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.

Consequently, (initial) G.fast nodes have a very low port density – typically 16 subscribers or less per system – and get deployed very close to the home. This results in a high CAPEX cost per user. On the other hand, G.fast enables a faster adoption of FTTH services, avoiding the need to rewire every front yard and multi-dwelling unit.

Next generation G.fast chipsets will have improved density and it is expected that also the vector processing functionality will grow, allowing future G.fast systems to scale to more ports (up to 96 ports). But its density will remain less than Vplus.

The ITU-T is currently working on an amendment 2 to the G.fast standard which aims to improve performance on loops up to 300m with targeted aggregate bitrates of 300Mps over 300m in overlay of VDSL2. This amendment will improve overall performance on longer loops but will not eliminate the density and time to market challenges that Vplus can address today.

VDSL2
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 550m to 1000m. Since VDSL2 17a is widely deployed today, it offers a fast and cost effective upgrade path to 100+Mbps with vectoring.

Vplus
Vplus, with its 35MHz spectrum, supports both longer loop lengths (200Mbps over 500m) 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, the Vplus reach is a very good match for many existing FTTN deployments. Vplus can provide a quick and easy upgrade path for operators that are already deploying VDSL2.

COMPATIBILITY WITH EXISTING VDSL2 VECTORING DEPLOYMENTS

Using higher frequencies 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.

VPLUS allows mixed vectoring with VDSL2 17A

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 (35b) and 17a lines, and thus mixed deployments and a smooth introduction of Vplus. Since only tone spacing changes, existing 30a band plans could in principle be reused (although limited to 30MHz). However, on request of operators new 35b band plans reaching out to 35MHz have been adopted by ITU-T (in Annex B of the VDSL2 standard).

Alcatel-Lucent brought Vplus to the ITU for adoption. As a result, Vplus has been standardized as VDSL2 profile 35b, described in a new Annex Q of Amendment 1 of the VDSL2 standard (G.993.2 2015). Approval was reached in November 2015.

For operators that already deploy VDSL2 17a vectoring, Vplus offers a fast and cost effective upgrade path to 300Mbps services on short loops without the need for bonding or deploying new cabinets. As existing VDSL2 17a vectoring and Vplus lines can be mixed in the same cable without performance impact, only subscribers that sign up for the premium Vplus service need to change CPE.

It's All About Coverage

Vplus can be deployed in a number of ways (Figure 4):

  • Boost short FTTN lines - In an existing VDSL2 cabinet deployment, Vplus can be used to boost the speed on medium to short lines (<550m).
  • New FTTN/FTTCurb deployments - New deployments can obviously be planned and designed for Vplus’s sweet spot in terms of loop length.
  • Boost long FTTN lines - If many loops from the cabinet are longer than 550m, the two approaches above can be combined with the deployment of smaller cabinets in between the existing cabinets, bringing all subscribers within 550m or less of the closest Vplus node.

Vplus can be deployed in a number of ways

Figure 4. Vplus can be deployed in a number of ways

THE VPLUS OPTION

Vplus provides an additional option for service providers trying to solve the bandwidth equation. Positioned between VDSL2 17a vectoring and G.fast, Vplus doubles bit rates on short loops compared to VDSL2 17a vectoring at a much lower cost than G.fast and with significantly higher density (up to 100-200 users per node).

Vplus seamlessly falls back to VDSL2 17a performance on longer loops and allows for maximum re-use of existing FTTN investments. In addition, Vplus can be mixed with VDSL2 17a vectoring in the same binder without compromise, providing a smooth evolution path from 17a vectoring to Vplus.

To contact the authors or request additional information, please send an email to networks.nokia_news@nokia.com.