Is ADSL3 the next broadband over copper technology?

Linksys WAG54GS ADSL2+ Modem Router

Linksys WAG54GS ADSL2+ Modem Router (Photo credit: Wikipedia)

We can resoundingly give readers both a yes and no.

Part of the issue when talking about ADSL is the naming convention. ADSL is the “name” associated with broadband over a copper POTS line. POTS, plain old telephone service, is the common name for the copper line coming into most homes. It was originally developed simply to carry a telephone signal.

But ADSL is so ubiquitous for broadband over copper that the name ADSL tends to get abused. The confusion is so pervasive, even news reports sometimes mistakenly call other technologies ADSL, thinking such terms as VDSL and ADSL are interchangeable. But this is not the case. To clarify the issue, let’s look at different current types of ADSL.

ADSL is an “asymmetric digital subscriber line”. It works by using frequencies not needed for voice communications. This is why you can use an ADSL line for both voice and data communications at the same time. When ADSL came out, the theory was simple. It split frequencies on the telephone into 3 groups – voice, upstream and downstream.

Regular voice calls get relegated to an area from 0 to 4 KHz, an area between 25.875 KHz and 138 KHz is used for upstream (your computer sending out data), and an area from 138 KHz to 1104 KHz is used for downstream (getting content from the net to your computer). This is why it is called asymmetrical – the downstream is far larger than the upstream, under the premise that you’ll download a lot more from the net usually than you will sent to it. But ADSL is all covered under a standard called ITU G.992.1, which governs the mechanics of how ADSL must operate.

ADSL2+ was the next solid advance in ADSL speeds. It doubles the number of bits that can be transferred simultaneously. It does this by moving the upper frequency threshold from 1.1 MHz to 2.2 MHz which, theoretically, doubles the downstream transfer rate from 12.0 Mbit/s to 24.0 Mbit/s. Looking beyond ADSL2+ is where the naming conventions get a bit confusing.

Many nations, particularly in Asia, have been advertising ADSL3. While their products actually do offer faster speeds than ADSL2+, the technology itself is not actually ADSL based, but rather VDSL. VDSL gets most of its speed not by increasing the frequency range of signals over a long range, as ADSL 2+ does in regards to ADSL, but instead by using new hard wiring. VDSL runs, instead of copper, high speed fiber optic cabling out to a nearby hub by the customer.

VDSL2, particularly, does use a wider spectrum of signal, going up into the range of 12 MHz to achieve downstream rates of up to 200 Mbit/s. However, this incredible high speed can only be maintained for short distances, unlike ADSL, before it needs to be picked up and relayed down fiber optics. More to the point, VDSL is a different protocol. It is regulated under ITU G.993.1 (note that all ADSL is covered under G.992.* specifications). Check out the iiNet NBN coverage map and rollout plan on their new page.

So, while data speeds over copper may be seen to increase in speed in the foreseeable future – ADSL3 will not necessarily be the protocol of choice. It should also be remembered that telcos (telephone companies) are beginning to have to compete for voice services with local cable companies. This, in turn, has forced telcos – such as AT&T – to consider competing in television entertainment to keep a level playing field. This is important because it is an incentive for telcos to run fiber optic lines out to consumers. If that occurs, trying to eek more speed out of ADSL would be a wasteful expenditure of research when VDSL will already be available, a mature technology, and ready to compete with the bandwidth offered by cable companies over coax lines.

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