The future of DSL is something that many have been worried about, especially the high performance of fiber optics and increased focus on wireless technologies. Before looking into some of the future DSL technologies, it would help to look at what DSL technologies have come and gone as well as those technologies that have come and evolved. After all, learning about the past and present is useful when predicting the future of technology.
The Rise of DSL
One of the key traits that has made DSL a successful broadband technology is the fact that DSL uses the same twisted copper wires that telephone networks use. At the dawn of the broadband era, barely a decade ago, alternatives to DSL included many solutions that not use existing wiring such as ISDN (Integrated Services Digital Network) lines and T1/T3 solutions. One of the reasons that these alternatives were not widely adopted was their pricing, which was directly tied to their use of special wiring that was not readily deployed.
Early DSL came in two basic flavors: ADSL (Asynchronous Digital Subscriber Line) and SDSL (Synchronous Digital Subscriber Line), the former mostly intended for consumers while the latter was, and still is targeted at certain businesses and enterprises with greater upstream speed requirements. While SDSL offered equal upstream and downstream speeds, it would be the high download speeds of ADSL that most consumers would eventually find attractive, and thus modern forms of DSL still offer asynchronous communication that favors faster download speeds than upload speeds.
Some forms of early DSL did not make it, such as ISDL, which used DSL technology over ISDN lines. SDSL may also be considered to be something of a failure by some standards as it is not nearly as common as ADSL and ADSL-derived standards. The one thing that these standards seem to have in common is the lack of performance for their price. Looking at modern DSL technologies, it is hard to argue that they are anything but an good value considering their performance levels. The performance offered by the least expensive DSL plans today is similar to high-end DSL plans of only a few years ago, and DSL prices have consistently gotten better over time in relation to performance.
The Current State of DSL
There are many kinds of DSL (Digital Subscriber Line) services on the market today, but VDSL (Very high speed Digital Subscriber Line) seems to be the dominant technology at this moment. VDSL is currently in its second generation, which is often referred to as VDSL2 by industry insiders. VDSL2 comes with a wide range of profiles, which means that just because two carriers offer VDSL2-class services does not necessarily mean that the underlying technology is the same, or even entirely compatible.
AT&T uses Alcatel-Lucent VDSL2 equipment in most of their curb-side cabinets, which in turn are primarily fed data via fiber optics. This put AT&T in a position to deliver their next generation of U-Verse on a VDSL technology, fiber optics, or a combination of the two. While it is unlikely that AT&T will move to FTTH (Fiber To The Home) meaning a 100% fiber optic network such as Verizon’s FiOS, the do have plenty of options to consider that might offer impressive speed boosts to consumers.
Companies such as Versatek market 100 Mbps downstream / 20 Mbps street cabinet systems and DSLAM components, which providers such as Summit Broadband have adopted. While their offerings may not necessarily reach the limits of these components, they are still impressive and easily demonstrate that DSL still has a lot of life left in it, though it is clear that copper wiring is approaching its limits in its current form.
Another option that started to gain traction in the industry around 2005 or so was the use of naked DSL, sometimes referred to as NDSL. Naked DSL is a form of broadband that could easily take off in the future as the entire line is available to the DSL. There is speculation that by allowing data to communicate over a greater range of frequencies that additional performance can be gained via multi-spectrum transmissions. It is important to note that the current and past use of the term NDSL was primarily related to business, while the future use might be more of a technical specification. That is to say that NDSL using existing technologies that work with or without an analog phone are very different than proposed technologies that require use of a greater range of frequencies and thus cannot be paired with an analog telephone service.
GDSL, a Future FTTH Contender?
With fiber optics seeming poised to take over the broadband arena in the coming decade, providers with extensive infrastructure are looking to find new ways to compete. On the DSL front, gigabit DSL (GDSL) is one such technology that appears promising. There are various GDSL specifications being proposed and debated, but most of them rely on naked DSL, which means that carriers such as AT&T would probably offer GDSL with some form of VoIP technology since using an analog phone in conjunction NDSL would not be possible.
What makes some of the GDSL specifications impressive is their use of multiple pairs of copper wires. While current DSL systems almost uniformly use a single wire, GDSL uses multiple wires to create a MIMO (Multiple-In/Multiple-Out) approach. MIMO technologies have proven very effective with wireless networks, but whether or not MIMO will prove equally effective for consumer-grade DSL is a question that may be answered someday soon. The question is: When?
Unfortunately, the first specification(s) for the generation of GDSL technologies has yet to be finalized. This means that GDSL might be over a year away, as carriers will need to evaluate the technology and making any final decisions that will ultimately effect the future of broadband.