New tech may bring near-gigabit speeds to DSL... someday

New tech may bring near-gigabit speeds to DSLIn the US at least, if you don't already have fiber to your home, it looks like you're very unlikely to get it any time soon, since the telcos are shying away from the cost of installing that infrastructure. Unfortunately, that leaves these same companies at risk of falling behind cable ISPs, which are starting to push speeds that only fiber can currently match. There may be a bit of good news for telcos that are uninterested in replacing their copper infrastructure, however, as a number of technologies are now being demonstrated that can push DSL speeds to well beyond the 100Mbps mark, with most of the announcements being timed for this week's Broadband World Forum.

To understand the challenge of getting that bandwidth out of a pair of copper wires, it helps to have a basic understanding of DSL, which uses the paired copper wires that were deployed for standard phone service. A signal can be sent transmitted as a difference between the two wires. Standard phone service uses one frequency band to transmit its signals, but that leaves many other frequencies free to act as potential carriers of data signals. The primary limit of DSL is distance, as the problems inherent to DSL degrade the signal slightly with each meter.

One of the biggest problems with DSL is crosstalk, where a signal on one of the wires induces noise in its neighbors. This both cuts down on the number of frequencies that can be used effectively and requires sophisticated noise detection to get more bandwidth out of the ones that are in use. So to get more bandwidth, ISPs need to do some combination of adding more wires, adding more frequencies, and improving their ability to eliminate noise. The new technologies, which enable speeds to close in on the 1Gbps barrier, use a combination of all of these.

Adding more wires doesn't necessarily mean physically adding them to the home; many homes are equipped with multiple phone lines, and it's possible to bond two or more of these together to get increased bandwidth using existing DSL technology—a route that is already being taken by AT&T. Most of the new technology involves a combination of additional pairs and some improved noise correction. For example, the Hong Kong company Huawei is testing a system it calls SuperMIMO that involves a set of four twisted pairs, with noise correction that squeezes up to 175Mbps out of each pair, giving it a capacity of 700Mbps overall.

Nokia Siemens, however, appears to be claiming that it can add additional channels without requiring a boost in the number of physical wires. The system, called "phantom DSL," layers an additional signal on top of the standard DSL frequencies in order to create a virtual channel that can also carry data. Alcatel-Lucent's Bell Labs announced a similar system back in April, which it claimed could maintain speeds of 100Mbps out to a kilometer, and reach significantly higher speeds at shorter distances (300Mbps at 400m). Nokia Siemens is claiming to get even better performance, with speeds over 800Mbps at 400m, though no word about the bandwidth at the kilometer mark.

Although this is a lot easier than running additional phone lines to residences, the technology would require new hardware at the phone company's end, and new modems for the end users. The one quicker fix that seems to be on display at the Broadband World Forum comes from a company called Ikanos, which is selling a noise correction system that can be attached to existing DSL hardware in phone company facilities, and requires nothing new at the home. The system apparently acts a bit like a noise-canceling device for a DSL line, sending out signals that cancel interference, and enabling 100Mbps service over existing DSL equipment.

So, can those stuck with only DSL or cable expect to see a much more competitive offering from the telcos? As Broadband Reports notes, they shouldn't be holding their breath. The phantom DSL technology is still only in the testing and demonstration phase; there's no products yet. Only the Ikanos system appears to be ready for the market, and that doesn't offer such a radical departure in speeds.

When it comes to market, deploying any of this will cost money, even if it will be substantially cheaper than laying fiber. The telcos are likely to be unenthused about that prospect.

Source: ars technica

Tags: Internet

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