… perhaps for sufficiently small values of “four”…
In February 2008 two of Australia’s leading Internet Service Providers, iiNet and Internode, released an ADSL2+ broadband “heatmap”. It illustrated what a sample of 16,000 customers within the Sydney area were achieving in terms of real ADSL2+ broadband download speeds. The heatmap can be downloaded from the Internode website here and I’ve reproduced it below.
The map itself commits a few GIS sins including no scale or north arrow. And personally I find the chosen colour grading makes it difficult to differentiate between the top two speed cohorts. These criticisms aside however, the point that iiNet and Internode wanted to make is that 50% of metropolitan dwellings are technically capable of speeds of ~12Mbps or faster right now. And certainly the map seems to support their contention (ISP… contention… boom, tish!… *sound of crickets chirping in the background*).
It’s worth mentioning that the map is a political statement. iiNet and Internode believe there is no justification for laying down a new and very expensive Fibre To The Node National Broadband Network. They want to show that the existing copper infrastructure can deliver NBN-like speeds to a large swathe of the population today. Of course the irony is that both companies are part of a consortium (known as Terria) bidding to actually build the NBN – an NBN that neither actually want. I guess they decided it’s preferable to be Victor Frankenstein rather than one of The Creature’s innocent victims. Not that they have much to worry about. As at January 2009 the NBN appears no closer to being built than it was back in February 2008.
But back to the map. I have a problem with the map.
Let’s start with this graph on Internode’s website. It shows how fast ADSL2+ speeds can be, based on your distance from the exchange:
ADSL2+ download speeds drop off exponentially as distance from the exchange increases. 12Mbps or faster is possible at distances of up to 2.5kms. From that point onwards bitrates rapidly skid off the rails. Any kind of meaningful ADSL2+ “broadband” (i.e. >1.5Mbps) seems to crap out at approximately 5kms or so.
Now consider the ideal case. Imagine if dwellings are distributed randomly and uniformly around their exchange inside a perfect circle of radius=5km. Also assume (I admit unrealistically) that the dwellings are connected to the exchange via perfect, straight, radial lines. Dwellings within 2.5km of the exchange can download at 12Mbps or faster. Households located 2.5km to 5km can still get ADSL2+, albeit at lower bitrates. Any poor saps living beyond the 5km limit cannot get ADSL2+ at all.
OK, that’s a lot of assumptions. But proportionally π2.52/π5.02=25% of the dwellings are inside the 12Mbps-or-better red zone. A far cry from the 50% that iiNet and Internode are claiming.
Either I’ve made a hash of the whole analysis (highly likely) or something odd is going on. One possible explanation is that households who cannot get very fast ADSL2+ speeds simply don’t bother signing up for ADSL2+ at all. Many households outside the theoretical 12Mbps limit seem quite happy to stick with ADSL1 or some other product.
Something for me to ponder.