Speculatio in impedimentum

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Once the detritus of another Christmas had been cleared away, I started to read one of my gifts; for inevitably I had been given a copy of Steve Jobs’ biography and I found myself pondering the imponderabilia of innovation that optical fibre broadband presents and I am impelled to pen this piece, imperfect as it may be.

My blog [It’s the Law] on the impedimenta of copper-based broadband stirred up some debate over at www.ISPReview.co.uk, the first comment of which was the predictable imprecation by a “techy” of marketers; that I had been imprecise in my interpretation of the science, an imputation that my work was impure; that the real problem with copper when used as a physical medium to deliver broadband was not resistance as defined by Ohm’s law, but a more complex phenomenon known as impedance.

And I can’t deny an impudent sleight of hand. The broad theme of the piece was that fundamental laws of physics directly define real world telecom services and that the nature of these laws when applied to copper wire means that confusion rather than clarity is offered to consumers.

Rather inconveniently for my theme of “Laws”, there isn’t a “Joe Blogg’s Law of Impedance” as such, no nice, neat label to apply. In this sense, in the context and flow of the blog, impedance, although a more technically precise subject, didn’t fit, and neither did several other limiting factors of copper.

However, the impinging effects of copper as an impedor are well known and there are definitions and even formulae available to describe it, for those of a mathematical mind. Much effort is being invested to overcome these and other limitations; but even as millions if not billions of pounds of R&D is spent to wring every last possible bit out of this 19th century network technology, to sweat the asset as much as possible, the fundamental limits of copper are imprescriptible.

According to my ancient “Physics is Fun” textbook, impedance is defined as the effective resistance of an electric circuit or component to alternating current (AC), arising from the combined effects of ohmic resistance and reactance.

Reactance is the opposition to the flow of alternating current caused by the inductance and capacitance in a circuit, measured in Ohms. The total opposition to the flow of current in the circuit is the impedance, which is the sum of the reactance and the resistance in the circuit.

Or in other words, it’s Ohm’s Law plus.

One of the consequences of copper’s natural and indisputable opposition to the flow of electrical current of both varieties is the imprecision of broadband services that it delivers. When low frequency voice calls were all that copper had to deliver, service was ubiquitous and universal; the medium could deliver the message.

But now, it cannot; the high frequency services delivered frequently depend on your postcode. Precisely marketed with vague “up to” speeds, but with actual throughput not achieving anything like those advertised speeds, especially on the anemic uplink side of the service, leaving consumers disappointed, disaffected and dissatisfied with their service and distrustful of their service providers.

For example, here’s a Speedtest I just did on my own link at home in Maidenhead, 1 mile or 1.6Km (1600m) from the main exchange (although like the majority of consumers I have no idea what the copper distance is). The underlying technology is ADSL2+ and according to the graph in my previous blog I should be receiving circa 20Mbps on the download (which matches the advertised speed of 20Mbps).

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However, I am receiving less than 33% of the advertised speed (a whopping 70%+ loss!) and even less of the theoretical maximum that ADSL2+ offers, yet I am paying 100% of the tariff of a 20Mbps service. And to cap it all, my download data volume is capped.

The upload speed is advertised as being a derisory 1Mbps and I have access to only 30% less than this limit, which is substantially less than the minimum recommended bandwidth for a SkypeHD video call. Skype cannot improve their service offering until the network can deliver more bandwidth; the medium is impeding the message.

My service provider isn’t BT by the way, but according to BT’s line checker, I should be receiving between 7Mbps and 11Mbps downstream, which while being a welcome improvement is still significantly less than the advertised 20Mbps “up to” speed on my service provider’s website. And it’s this imprecision, unacceptable in other areas of technology such as the processor speed of a laptop, which is the whole point of my previous blog. (Question: why doesn’t BT’s line checker also estimate upload speeds?).

The imprecise nature of copper-based services is caused not only by impedance. Other impedimenta of the copper network include, inter alia:

  • thermal noise
  • echoes
  • reflections
  • attenuation
  • crosstalk
  • surge protectors
  • radio frequency interference (RFI) filters
  • bridged taps
  • split pairs
  • bunched pairs
  • leakage to ground
  • low insulation resistance
  • battery or earth contacts
  • high-resistance joints

Copper is already impeding the service experience that consumers have from the internet and it will always do so. Rather like a giant, distributed, severely limited backplane of a computer, it is limiting the creativity, innovation and revenue potential of the internet and of the economy as a whole.

“Impedance” is a derivative of “impede” which is from the Latin impedire, “to shackle the feet”, ultimately related to “pes” or foot. And for most of us, walking pace is about all that can be achieved with copper, especially on the uplink.