Wednesday, November 11, 2009

The shape of the backbone

I was all set to write a somewhat philosophical post comparing the internet backbone to the phone system that came before it, when I realized I know very little about the internet backbone. Since I claim not just to be writing about the web, but actually figuring it out (however slowly) as I go along, that seemed like a pretty embarrassing lapse. So I've started doing a little basic digging and, so as to have something to post while I'm doing it, pass along some of my findings.

There was a British general once who, whenever he was sent to a new theater of battle, would start off by making a crude, not-painstakingly-to-scale map of the major roads and rail lines in the territory, noting the distances between the most important cities, junctions and other points of interest. This exercise would pay dividends later, not just in the day-to-day running of the campaign, but in preventing blunders on the order of depending on troops to cover a week's worth of distance in two days. It would also give some idea of the political structure of the place -- who was likely to be trading with whom, who might not care too much about what was going on where, and so forth -- and help greatly in deciding which supply lines to guard where, which enemy supply lines to attack where, etc., etc.

Along those lines (minus the military perspective), it seems useful to start with a very large-scale look at the international internet backbone, with an eye toward who's connected to whom and with what capacity. Physical distance is not as important here, though latency can matter in some cases.

Here's just such a map, dating from 2005, prepared by TeleGeography research for the International Telecommunications Union. Please don't look at the part that says "Proprietary and Confidential". There are probably more recent maps available* but this should give a reasonable impression. A few things that jump out:
  • North America <-> Europe dominates, followed by North America <-> Asia with roughly 40% of that capacity, followed by everyone else, far behind. In particular, there is very little capacity, relatively speaking, directly linking Europe and Asia. If you're in Bangalore talking to Bucharest, you may well be going by way of San Francisco.
  • Capacity to and from Africa is almost negligible on this map, but see below.
  • Capacity on these scales is currently measured in Gbps (the document gives 5- and 6-figure numbers in Mbps, but most of that precision is probably spurious). That's pretty big compared to my home connection, but not really stunningly large considering how many people are involved. By comparison, the human visual system appears to have a capacity on the order of 1Gb/s, so the 500Gb/s pipe between North America and Europe is, in some notional sense, roughly equivalent to 500 pairs of eyes. Put more realistically, though, 500Gb/s is about 125,000 DVDs playing simultaneously.
  • What these numbers actually mean is a different question entirely. Suppose for example that everyone in the US wants to follow the European football leagues online -- not that that's going to happen anytime soon. Would those millions of viewers saturate the pipe? Hardly, since the main pipe only has to carry a few video feeds at any given time.
As I said, the big missing piece in the 2005 picture is bandwidth between Africa and the rest of the world. As of this summer, that bandwidth has gone from practically nothing to about 1.3 Tb/s ,or 1300Gb/s to put it in the same units used above. That's over twice the size of the Europe <-> North America pipe, a classic example of leapfrogging technology assuming we're comparing apples to apples. Even if we're comparing apples to pears it still looks like a pretty big pipe.

(*) Back in the days that bang paths roamed the earth, one could subscribe to a newsgroup which published frequently updated maps of the backbone as it then existed, meaning mainly a bunch of T1 and similar lines. A T1 line could carry about 1.5 Mb/s, or .0015 Gb/s, or about 0.0003% of the Europe <-> North America link.

1 comment:

David Hull said...

Note to self: never really followed up on the backbone