Can An Old Dog Learn New Tricks?
Wireline network operators are grappling with how to best provision the network for the connection speeds required to support bandwidth-intensive Triple Play services. By 2016, customers could be demanding services requiring 100 Megabit per second (Mbps).1 However, many existing networks are far from optimally provisioned to support speeds approaching the magical 100 Mbps rate. Fiber-to-the-home promises virtually unlimited bandwidth, but is not always cost-effective or logistically feasible to deploy for many network operators.
Newly developed DSL acceleration techniques may provide viable, cost-effective upgrade paths for fiber-to-the-node (FTTN) networks. Chief among them, VDSL2 vectoring shows promise. While not yet widely deployed, the International Telecommunications Union published a vectoring standard (ITU-T G.993.5) in 2010, and a handful of OEMs have recently launched vectoring equipment and systems.
Vectoring employs technology similar to that found in noise-cancelling headphones to mitigate far-end crosstalk (FEXT) interference, thus improving the transmission rate of VDSL2 to fiber-like performance. It is implemented at the DSLAM and the customer premises (modem) via VDSL2 vectoring chipsets. The technique has doubled or more downstream transmission speeds in Europe1 and reportedly can boost speeds to 100 Mbps on single-pair loops reaching as far as 1,800 feet from the DSLAM equipment.2
Vectoring can be implemented in conjunction with another acceleration technique, pair bonding, in which service to a home connects through two bonded wire pairs instead of one. Pair bonding entails assigning two DSLAM ports to each customer and is limited to homes where two pairs are already deployed. The technique can extend the reach of benefits reaped through vectoring up to 3,400 feet.2
Unfortunately, vectoring and other acceleration techniques cannot solve all of the industry’s service problems. In fact, communication service providers now realize that once they strip away the crosstalk with vectoring, noise caused by other issues lurking in the network become more apparent.3
In order to fully realize the benefits of vectoring, the copper network between the DSLAM and the subscriber must be maintained and in some cases upgraded. Proper bonding and grounding, high-quality connectivity and upgrading the blocks and block tails in cross-connect cabinets can improve the transmission rates in existing copper networks to better realize the full potential of investments in DSL acceleration. In addition, cabinet expansion solutions can provide a cost-effective way to upgrade existing cabinets to support high-capacity networks.
Upgrade existing terminals to utilize smaller-gauge DSL drops and Cat5 connectivity.
Low-pair-count cabinets installed near the customer allow for tool-less, quick, robust field termination of copper blocks.
Building entrance terminals should feature high-density, discrete, protected copper connectivity.
Bonding and Grounding Are the Basics -- Like “Sit” and “Stay”
A first step in conditioning the network for vectoring is assuring proper, high-quality bonding and grounding. POTS and DSL lines are generally robust enough to withstand a certain level of transmission noise. However, video services, such as IPTV, are highly sensitive to noise. Bonding and grounding are often overlooked but can affect the quality of video transmission, even in vectored circuits. One missing ground wire connection or loose nut on a bonding strap anywhere in the copper plant can cause excessive noise on the line, leading to pixelation, macroblocking, or complete loss of video.
Distribution cables are bonded and grounded at many points along the copper pathway: at cross-connect cabinets, to the MGNV (multi-ground neutral vertical) on electric utility poles, at network interface devices (NIDs), and in building utility closets. Proper bonding and grounding reduces power influence and prevents interference from high-frequency (AM) radio waves. At a minimum, National Electrical Code (NEC) and the National Electrical Safety Code (NESC) directives and industry standards for telecommunication bonding and grounding should be followed precisely. Connecting to the power company multi-ground neutral every 1,000 feet and at the end of the cable run or exposure can greatly reduce noise, including power influences.
Updated Training Techniques Help
Beyond that, replacing old, corroded bonding and grounding components with high-quality shield bond connectors and ground braids from a trusted manufacturer can help create secure connections and minimize noise. Lower-grade connectors and cables abound. They may save money in the short-term, but network operators will pay in the long-run when these products deteriorate too quickly and leave the network exposed to service interruptions, dissatisfied customers and expensive
Look for shield bond connectors specifically designed to create a stable, low-resistance electrical connection between the metallic shield of the communication cable and the bonding bus bar or ground wire source. A high-quality shield bond connector is made from tin-plated brass for corrosion resistance and is slightly curved. The curved design exerts a continuous spring force on the sheath after clamping, helping ensure a secure, reliable connection. For grounding straps, braided conductor rated to a #6 AWG equivalent and made of tin-plated copper offers mechanical strength, protection from corrosion and low DC electrical resistance as well as low-impedance electrical path to ground for stray AC/RF noise. Once again, seek out a trusted manufacturer for the most robust products.
Ensuring That Old Dog Performs Consistently
Network operators can deploy the highest category cable available and the very best active electronics. They can implement the most cutting-edge DSL acceleration techniques. However, if it’s all connected by old or subpar connectivity equipment (i.e., modular and discrete splices, closures, terminals, cross-connect blocks and protection) a network cannot realize its full potential in terms of transmission speeds (rate) and signal quality (reach).
Connector contact integrity is critical to ensure reliable service, not only at the time of installation, but over the life of the connector. A loose or deteriorated connection can cause a high-resistance open condition, attenuating the VDSL2 transmission or causing an electrical imbalance in the cable. This can leave the twisted pair more susceptible to noise and cause service errors. The fix often turns into a labor-intensive process because the offending connector can be difficult to pinpoint.
Again, the problem comes down to the age and quality of the equipment. Many network operators have upgraded to high-twist, high-capacity cable, yet they continue to use obsolete connectivity components designed to support Cat3 in field applications, negating much of the benefit gained from upgrading the copper plant.
Some who do replace their connectivity often choose inferior-quality products that put their network at risk of transmission troubles. Low-quality connectors use inferior materials and/or manufacturing processes and tolerances. These products may not last as long or provide the same high-quality transmission characteristics as superior products.
For instance, a poorly constructed insulation-displacement contact (IDC) element can lead to unreliable connections down the road. Moreover, block terminals that require special tools for proper connection also require ongoing calibration of those tools over the functional lifetime of the connectivity device to maintain the originally specified terminal performance, complicating network maintenance.
Every connection point in the FTTN/xDSL OSP copper network marks an opportunity for signal degradation. Indeed, some loss occurs at every connection point -- that’s unavoidable. However, loss can be minimized. Replacing aging connectivity components with high-quality, robust, high-twist-compatible connectivity equipment that is easy to install can help ensure reliable connections, reduce noise and simplify maintenance. A small investment in high-quality connectors delivers a big payoff in terms of long-term network reliability and reduced truck rolls.
Cabinet Expansion Helps Old Dog Stay Safe
DSL acceleration techniques will often require larger pair counts in cross-connect cabinets. Pair bonding, for example, could theoretically double the number of pair counts coming out of the remote terminal. Traditionally, this means identifying rights-of-way, wading through regulatory processes, pouring concrete pads and installing new cabinets in neighborhoods where residents may see them as an eyesore.
There’s a better way. Cabinet expansion and retrofitting techniques exist that allow operators to increase pair count within the existing footprint. Extension panels and frames can be used to enlarge the enclosure. Existing blocks can be retained and expansion blocks added to deploy pair bonding. Cabinet expansion can increase the capacity of a cabinet by 50 percent and without interrupting service.
WithVDSL2 reaching for 100 Mbps per second, existing copper networks may soon reach their limits. DSL acceleration techniques, such as vectoring and pair bonding, show great promise in boosting the bandwidth of existing copper networks to current performance requirement levels competitive with fiber. This is great news for operators who wish to leverage their investment in their copper OSP. However, acceleration techniques alone cannot deliver the highest speeds possible. Copper infrastructure must be conditioned to improve signal and reduce noise. By investing in high-quality infrastructure products for their copper distribution networks, wireline operators -- and their customers -- will realize more benefits from DSL acceleration.
1. Graham Finnie, “DSL Acceleration: Making it Work” whitepaper, Heavy Reading, June 2012.
2. “Vectoring: Accelerating the Delivery of Ultra Broadband Services” pocket guide, ADTRAN, October 2012.
3. Stephen Wilson, “DSL acceleration: Simple concept, complex reality” blog post, Informa, December 2011.
Robert Mertz is a product marketing manager, 3M Communication Markets Division. He has more than 30 years of experience in telecommunications in the United States and Europe. David Senum is a product marketing manager, 3M Communication Markets Division. He has more than 35 years of experience in telecommunications and semiconductors. For more information, visit www.mmm.com/telecom.
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