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Issue 20 Articles

Voxbone logoAn Overview of
G.993.5 Vectoring

Extract from one of the latest Broadband Forum's Marketing Reports (White Papers)

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Current broadband penetration approaches 600 million lines worldwide and continues to grow at a rate of over 12% per year [4]. As is shown in Figure 1, DSL remains the dominant broadband access. VDSL2 (ITU-T G.993.2 [6]) provides a growing proportion of both the DSL component as well as the final leg of the broadband access connection in solutions listed by Point-Topic in Figure 1. Not only is deployment of broadband increasing rapidly but also the bandwidth and quality of service requirements of the applications demanded by users continues to increase. While relatively recently bandwidths in the range of 5 to 10 Mbps toward the customer were considered to provide an acceptable premium broadband service, today significantly higher bandwidths are required to support requirements for services such as High Definition IPTV and bandwidth requirements continue to increase as application capabilities evolve. Bandwidths considerably in excess of 30 Mbps toward the customer premises are necessary to deliver the emerging advanced services.

Figure 1 - Broadband access-connections for Q4 2011, (source Point Topic: 2011 Year End report - 2012)
Figure 1 - Broadband access-connections for Q4 2011, (source Point Topic: 2011 Year End report - 2012)

In 2010, ITU-T published the G.993.5 Recommendation, Self-FEXT Cancellation (Vectoring) for use with VDSL2 transceivers[5] , informally known as G.Vector that allows DSL connections to meet these enhanced requirements. VDSL2 deployments based on this new Recommendation facilitate achieving the quality of service required for premium services such as multiple channels of HDTV (MR-180 [3]). Systems based on the G.993.5 Recommendation have the potential of being deployed in the field as an enhancement to existing DSL deployments thus reducing capital investment cost as well as simplifying operations at the network operators.G.993.5 achieves its improvements by canceling, using a mathematical process known as Vectoring, the majority of DSL's crosstalk noise. Since the DSL Lines in a cable no longer interfere with each other the total throughput of each line and the total throughput of all lines in the cable is significantly increased. G.993.5 is capable of supporting connection speeds in excess of 100 Mbit/s at distances up to 500m (1500 ft) from a fiber fed DSLAM using VDSL2 on typical telephone wiring1. Even with loops as long as 1200m (4000 ft) rates toward the customer (‘downstream’) that exceed 40Mbps over a single copper pair are supported.

With its potential for increased bandwidth using VDSL2 technology, G.993.5 is being considered by a number of carriers to enhance their DSL based network services. MR-257 provides an introduction to this vectored VDSL2 technology, its applicability and the opportunities and issues raised by its field deployment.

DSL access over copper twisted pair provides many advantages for the Network Operator. These include operational ease of deployment, reuse of existing copper infrastructure thereby reducing the include operational ease of deployment, reuse of existing copper infrastructure thereby reducing the resource requirements to deploy new fiber, and ease the termination at the customer's premises. Reuse of existing copper has many advantages. Data throughput over DSL is dedicated rather than shared to the customer and DSL’s use of fiber to connect remote DSLAMs reduces fiber-deployment by sharing it between 10's to 1000's of customers connected to a remote DSLAM. In many cases, especially ‘brown-field’ situations, the resource requirements for deploying fiber all the way to the customer’s premises can exceed the benefits of the enhanced services to the Network Operator and thus the deployment of fiber does not occur. In such situations DSL over copper for the final segment of the broadband connection may be the only viable broadband solution. However unless DSL supports the bandwidth requirements for the newly emerging services, the economic situation described above results in a large group of ‘have-nots’ whose broadband service is second rate compared to those served by fiber solutions. The ITU-T G.993.5 Recommendation, Self-FEXT Cancellation (Vectoring) for use with VDSL2 transceivers[5] , informally known as G.Vector, provides a solution to this problem. As G.993.5 compliant equipment is developed the potential for improved bandwidth over VDSL2 connections is large. However the Network Operator deploying G.993.5 must address a number of operational and architectural issues in order to realize the benefits of Vectored DSL. Among these issues are (1) dealing with complexities in cable and binder management introduced by vectoring, (2) selecting which lines will benefit most from vectoring and (3) ensuring that noncrosstalk related noise that cannot be canceled is ameliorated by DSL Quality Management (DQM) techniques.

Conclusion

Vectored DSL as defined in ITU-T Recommendation G.993.5 supports line speeds of greater than 100 Mbps on loops up to 500 meters in length, enabling the most advanced application services to be carried over copper. With appropriate placement of DSLAMs, use of management tools and techniques such as bonding of Vectored lines and use of DQM techniques, Vectored DSL becomes an important tool for network operator to provide broadband services such as IPTV to all their customers. Although deployment of Vectored DSL raises new operational issues for the network operator, the management tools provided in both in the ITU-T Recommendation and in the work of Standards Development Organizations such as the Broadband Forum are ensuring that G.993.5 is emerging as a complete ecosystem that will quickly enable its potential. The emergence of Vectored DSL provides the DSL based service provider with the tools that facilitate supporting the bandwidths required for higher valued premium services over their existing copper based networks and helps ensure that deployment of DSL increases as Broadband Services continue to evolve.

The full version of this report is available from:
www.broadband-forum.org/marketing/download/mktgdocs/MR-257.pdf

Comments or questions about this Broadband Forum Marketing Report should be directed to: info@broadband-forum.org.

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