Vectoring 101

by david.nunes
Dror Gonen Issue:North America 2012
Article no.:10
Topic:Vectoring 101
Author:Dror Gonen
Title:Head of the Access Line of Business
Organisation:ECI Telecom
PDF size:262KB

About author

Dror Gonen joined ECI as Head of the Access Line of Business in May 2009.
Prior to his current role, he was the CEO of Deltathree, and previous to that he was Vice President of Content Solutions at Comverse, a company where he held various roles in R&D, marketing and management.
Dror Gonen holds Bachelor of Science degrees in Electrical Engineering and Physics from the Technion, both with distinction, and an MBA from Bar-Ilan University.

Article abstract

Many operators find it hard to justify the high cost of fiber and are looking to postpone this considerable outlay, but they still need to combat subscribers churn and growing expectations of high speeds. VDSL (very high speed DSL) purports to enhance DSL, but is crippled by ‘crosstalk’. VDSL2 with Vectoring overcomes this problem. The DSLAM compensates for upstream or downstream noise and interference occurring in the cable, thus allowing higher reach, higher bandwidth and improved performance. Vectoring allows operators utilizing their copper assets for longer, yet compete in the market and even introduce more demanding services.

Full Article

We live in a world of intensive telecommunications. Everything we do is somehow connected to the way we communicate. Extending our personal lives into the office and our work life into our homes – with our Blackberries and smart phones and tablets – our lives get entwined to an unprecedented level. We take it for granted that this is the way it’s supposed to be– when we go to a coffee shop with our laptops, we expect a Wi-Fi connection. When we travel, we look for the most efficient and cost-effective way to communicate transparently – that is, as if we were still in our home networks.

As an end user, I expect the network to be ’there‘ – in my home, in my office, in the airport, in the coffee shop. As an end user, what’s behind my connection is of no importance. Sure, I need a certain amount of bandwidth to support my basic voice, data and video needs (hopefully the days of endless buffering is behind us). I am not, however, looking at my cables and wondering, is that a fiber-to-the-home connection or am I connected with VDSL2? I am looking at my bandwidth needs, and I will let my telco worry about providing the necessary network infrastructure to provide me with what I want.

From the telco perspective, of course the equation is not so simple. After all, the telco’s business is the underlying infrastructure. Most established operators are sitting on extensive copper networks, and are slowly upgrading to fiber, to cope with the demand for more services and bandwidth. These telcos’ pain point is how to deliver what I demand in terms of bandwidth and services, while keeping an eye on their return of investment. If they don’t upgrade – and conversely don’t offer the necessary bandwidth and services – their customers will probably look elsewhere for an alternative. If they upgrade too fast, before there is a mass of customers willing to pay for the extra bandwidth and services, they will be hard-pressed to justify that level of investment.

So what’s a telco to do?

VDSL Technology
In an ideal world, we would all be connected with end-to-end fiber. Fiber today provides the highest bandwidth available, either through residential GPON or enterprise point-to-point Active Ethernet, and is indeed future-ready as it will carry any future connectivity technology. Deploying fiber, particularly in residential centers, is an expensive proposition so telcos started looking at how to optimize what was already in place – their copper infrastructure.

Copper networks are very versatile, and a particular technology – VDSL, or very-high-speed DSL technology – brought promising bandwidth when initially introduced in early 2000. While it’s true that speeds of up to 100 Mbps are theoretically possible using the technology, in reality the practical rate and reach of VDSL are limited because VDSL (and its successor VDSL2) suffers from a severe limitation, namely crosstalk interference. Crosstalk interference means that VDSL2 lines are sensitive to electromagnetic noises coming from adjacent copper pairs, degrading the signal quality being transmitted through the wire.

The consequence of this limitation is that the potential bandwidth of VDSL2 is significantly reduced. If theoretical VDSL2 performance (in an ideal, no-crosstalk environment) was a viable alternative to Ethernet-over-fiber, real-life performance would still not be adequate.

This situation is changing.

The vectoring option

In 2006, a group of top DSL researchers from leading universities, carriers and vendors formed the iSmart Consortium in order to carry out research in the field of DSM (dynamic spectrum management). DSM was then a promising technology to address the limitations of VDSL technology, namely crosstalk. The result of their work eventually became DSM Level 3, or VDSL2 vectoring (ITU-T G.993.5, also known as G.vector).

VDSL2 vectoring helps wireline operators significantly mitigate crosstalk, and offer bandwidth and distance performance which approaches that of theoretical, noise-free VDSL2. It works by processing and limiting the interference that occurs between twisted copper pairs. In doing so, it enables higher-speed services to be provided over longer distances in existing copper access loops.

The performance enhancement effect that VDSL2 vectoring brings can be illustrated with two examples. Let’s look at potential offerings from our telco to its subscribers. Let’s assume that the network is composed of 0.4 mm copper wires (for those telcos with thicker copper wires, the bandwidth potential is even higher).

a. 80 Mbps premium service – before VDSL2 vectoring, telcos could not provide this kind of bandwidth to subscribers, as the degradation in quality was too high. With vectoring, all subscribers within a 400 meter radius from the street cabinet can sign up for it.
b. 50 Mbps service – before VDSL2 vectoring, only subscribers within a 400 m radius could receive 50 Mbps. With vectoring, the telco can expand the service radius and coverage to 800 m, reaching 300 per cent more subscribers.

Both these examples are illustrated in the graph below.

Vectoring-enhanced downstream bandwidth

For these reasons, vectoring is becoming the technology of choice for enhancing deployed copper to superfast speeds in the residential and business markets. In fact, market analysts are predicting that VDSL2-based networks will dominate the xDSL-based access network by 2014 and will be a major part of most next-gen access networks.

Digging deeper: how vectoring works

Vectoring addresses the issue of crosstalk interference, eventually allowing higher speeds over farther distances. Crosstalk is the electromagnetic interference caused by the simultaneous transmission of signals in copper pairs that are bundled together in a feeder cable, which can typically contain 100 or more pairs. The proximity of the copper pairs in the feeder cables causes this noise, which can lead to increased error rates and degradation in bandwidth, with results in the field limited to 24 Mbps at 1000 meters.

Let’s go a little deeper and explore how vectoring actually works to alleviate this interference.
The most common source of interference in VDSL2 networks is FEXT (Far End crosstalk). FEXT distorts transmitted signals, as the signal emanating from one pair interferes with the signal being transmitted in an adjacent pair. This increases noise levels and results in bandwidth degradation.

A vectoring DSLAM makes a number of adjustments in order to negate the effects of FEXT:
 Downstream: With the help of vectoring-friendly CPE, the DSLAM measures the crosstalk coupling introduced by FEXT and pre-codes its transmission with ’anti-noise‘ corrections.
 Upstream: The DSLAM receives the noisy transmission and uses the FEXT measurements to post-process the received signals and remove the crosstalk imposed by the other pairs.
The result is simple: more bandwidth over longer distances, for more advanced services.

The business case for vectoring

The economic justification for vectoring can be established by examining the benefits to the telco, which are:
• Increased revenue per subscriber: With its typical 50 Mbps rate, vectoring enables operators to offer very-high-bandwidth services and applications to subscribers. These premium services can bring in 20-35 per cent more revenue than standard services. They can also be delivered more affordably because there is no need to invest in a costly FTTH deployment, until there is a critical mass of subscribers willing to pay for that.
• Reduced customer churn: Typically, wireline churn exceeds five per cent per year in many markets, and the reasons for churn are often directly related to competitive offerings in those markets. Vectoring allows the telco to offer service packages that are competitive with new entrants’ or cable companies’ offerings on a price/performance basis, dramatically reducing churn and even helping to win new customers.
• Postponed investment in new fiber access infrastructure: FTTH is the ideal solution for the long term, but the massive capital outlays associated with such a deployment – between US$1,000 and US$2,000 per subscriber – make it cost-prohibitive. Additionally, long deployment schedules can result in delayed ROI (Return on Investment) while costs relating to construction issues can pose additional CAPEX implications. Vectoring is a viable option for operators who want to prolong the life of their copper infrastructure without undertaking significant new CAPEX. Despite postponing FTTH, vectoring allows them to immediately offer premium services over their existing network.

Turning challenge into opportunity

These days, telcos are facing considerable competitive challenges from new entrants or other providers. Vectoring brings a viable answer to the issue of more bandwidth over the existing infrastructure. Vectoring enables telcos to extend the life of their existing copper plant and postpone extensive capital investment in new fiber infrastructure.

With vectoring, wireline operators are now able to offer very-high-bandwidth with next-gen services to their subscribers, increasing ARPU and reducing customer churn – all while planning for the transition to fiber at a pace that’s right for them.

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