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Cable Technology Feature Article

April 10, 2012

New Ofcom Rules Broadband Advertising Illustrate the DSL Problem

By Gary Kim, Contributing Editor

A survey of over 1,000 Think Broadband users suggests many are unimpressed with new broadband advertising rules for providers of digital subscriber line service in the United Kingdom.


21 percent of respondents think the rules does not go far enough. Regulations mandate that broadband service providers list 10 "speeds" that at least 10 percent of a provider's customers can experience.

Many would prefer a standard that advertises speeds about half of all potential customers can get can get. Some 33 percent of respondents prefer a figure of merit that describes "median" speed, while 43 percent prefer a "full" table of speeds.

How that could be done is not so clear, since any such table might only show speeds at various distances from a cabinet, itself not useful information for any specific customer at any location.

But that’s the whole problem with describing DSL user experience or speed at any specific location. It “depends” on many underlying circumstances, especially distance of any DSL modem from a modem access controller, the quality of the wire, any impairments to the integrity of the cables and interior wire and sometimes weather.

The reasons are simple enough. DSL uses a baseband signaling method, where electrical signals are directly transmitted through copper wiring. As with all transmissions, signals exponentially decay with distance.

That means speeds will be lower, the farther an end user is from the point where the signals launch. To be sure, cable modem signals traveling over coaxial cable are not immune from attenuation, either. In fact, cable modem signals decay at differential rates depending on the size of the cable, the specific frequencies used, as well as distance.

But the copper portion of a cable network has one salient difference from a DSL copper network: cable networks can use repeaters to boost the signal back up. Modem networks can therefore maintain higher signal strength and subsequently higher speeds, at virtually every location on the network.

That’s never true for a copper DSL network. The caveat is that on fiber “close to the home” networks, it is theoretically possible to keep the copper drops short enough to maintain high speeds at virtually every location on a DSL network.

In North America, most DSL networks with fiber trunking pull fiber to locations that are neither “to the home” or “close enough” to prevent most of the signal attenuation issues.

Areas with more-dense housing will do better. U.K.'s Origin Broadband is launching new broadband access services offering "faster than 40 Mbps service" starting in May 2012.

The  £35.50- per-month version will run VDSL2, allowing some to reach speeds of 100 Mbps, depending on how far they are from the Origin optical transceiver – a cabinet, usually.

Short access loops are the key to higher speeds using digital subscriber line technology. That is one reason European service providers often are less keen on investing lots of their own money in fiber to the home: in dense urban areas in Western Europe, DSL works just fine, compared to current fiber services.

In North America or Australia, which have lighter populations and consequently longer access loops, DSL hasn’t performed as well. The cable industry's marketing argument that DSL is "old" technology is clever, but not entirely correct.

Access loop length is the issue for all versions of DSL, since signal attenuation for any baseband signal is an issue. Of course, signal attenuation is an issue for all communication systems, but cable systems can use repeaters (amplifiers) on their copper network.

The fundamental problem with DSL is that it really is not easy to describe the actual speed any user will get, at any location. That poses obvious marketing challenges, as the new Ofcom rules simply illustrate.


Edited by Braden Becker

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