Deployment of New xDSL Technologies, Challenges and Opportunities

Deployment of new xDSL technologies, including vectored VDSL or G.vector, Super Vectoring or VDSL2 35b and G.fast is a significant opportunity for broadband service providers as it opens many opportunities for offering new services and enhanced revenue streams. Vectored VDSL and Super Vectoring can deliver rates in the order of 250 Mbps while G.fast is targeting 1Gbps at a significantly lower cost compared to fiber-to-the-home (FTTH) installations. A number of studies suggested that the deployment cost is lower at least by a factor of five for vectored VDSL and by a factor of two for G.fast. Although the deployment cost of these new xDSL technologies is estimated to be substantially lower relative to FTTH, it still represents a major investment, which service providers need to carefully plan, deploy and operate in order to maximize their return on investment (ROI).

Service providers upgrading their access network to vectored VDSL or G.fast are faced with various challenges for achieving their desired ROI. The main challenges can be summarized briefly as in the following:

  1. Service qualification: Service providers require reliable projections for data rates that can be delivered for these new services. They rely primarily on attenuation-based qualification rules that predict the achievable rates based on loop attenuation inventory. However, this approach does not take into account the effect of non-crosstalk (alien) noises, physical loop impairments, and inaccuracy of loop inventory data on accuracy of the predictions. As a result, such attenuation-based qualification rules usually have high false positive rates (sunk costs), or if designed conservatively, they would suffer from large false negative rates (lost opportunities).
  2. Outside Plant “grooming”: Service providers require identifying and resolving pre-existing line faults that potentially limit or deteriorate the expected performance gain of these new technologies.
  3. Greater needs for stabilization: Vectoring removes Far-End Crosstalk (FEXT) among the vectored group of lines exposing them to alien and impulsive noise sources that were hidden under FEXT before vectoring. Moreover, G.fast employs a much wider bandwidth compared to VDSL2. This makes G.fast exposed to a bigger set of interference and impulse noise sources that can have serious detrimental impact on the service stability. These additional noises need to be managed to avoid any detrimental impact on the stability of the lines.

DSL Expresse (DSLE) Module Summary

ASSIA’s DSL Expresse™ offers the following various tools and modules to help address these challenges:

  1. Service Recommender and Predictor Module: ASSIA’s Service Recommender Module estimates the viable rates and services that can be offered reliably with new xDSL technologies. With potential shortcomings of attenuation-based qualification rules in predicting services with vectored VDSL and G.fast, ASSIA’s Predictor Module is a reliable tool required to enable the service providers to operate the new lines at the maximum possible rates stably.
  2. Diagnostics module: This diagnostics tool helps to identify loop faults and provide precise guidelines on maintenance actions needed in the outside plant and in-house wiring to enable these new technologies. Loop impairments limit gains from these vectored technologies. Because these technologies transmit over a larger bandwidth and also, they use vectoring to remove crosstalk, the impact of loop impairments is significantly higher on the performance compared to ADSL or VDSL. Moreover, with customer self-installation of CPE equipment, various in-house wiring issues are not cleared and would potentially deteriorate the performance, significantly in some cases; thus, there is a need to identify and resolve wiring and/or noise issues to maximize the gains offered by vectored services. ASSIA’s Diagnostics Module is also capable of analyzing the crosstalk coupling measurements among the vectored group of lines (in addition to DELT data) to identify faults and issues that would impact the performance. The crosstalk analysis provides additional guidelines for cleaning up the faults and wiring issues.
  3. Profile Optimization: The Profile Optimization Module manages and improves the stability. With potential exposure to other sources of non-crosstalk noise, there is a need for this profile optimization tool to monitor and if needed to address the impact of such alien and impulsive noises and avoid any detrimental impact on the stability and performance of the new services. Moreover, as lines are pushed toward their limits in these new deployments, the stability issues become more prominent and would negatively impact the experience of the customer if not properly addressed. G.fast employs G.inp physical-layer retransmission mechanism as standard for offering a more effective protection against impulsive noises. For vectored VDSL, G.inp is an option. ASSIA strongly recommends deploying vectored VDSL together with G.inp physical-layer retransmission mechanism and optimizing the configurations of G.inp for these new deployments to improve the stability of the lines. Unmanaged use of G.inp for both cases may hide performance issues (e.g., throughput drops) that would impact the user experience negatively.

Although any upgrade to a new advanced technology can be challenging and costly even when it leverages already installed copper lines, the use of tools like the modules outlined above available by ASSIA, can make the transmission much smoother while also yielding a higher return on investment.