BitTorrent creator explains just why BitTorrent works so well, that the formula is simply bytes downloaded = bytes uploaded.
I’ve always found Bram Cohen, author of the BitTorrent protocol, very fascinating, perhaps mainly because he’s allowed myself and countless others the ability to share content in ways still yet to be imagined.
So whenever he shares his thoughts on BitTorrent I always sit up and take notice.
In this case it’s nothing spectacular, but he does give a simple explanation of why BitTorrent performs so well why dispelling the myth that content popularity drives download speeds.
He writes:
There’s a classic fallacy because if one person stands up during a concert they get a better view, then if everybody stood up during a concert they’d all get a better view. This is of course is not true – they wind up slightly worse off by all standing, because they all compete with each other for a view. The same thing happens with downloading from a server. In general, web servers will give about the same rate to every client downloading from them, so if you open many more connections than everybody else you get a greater proportion of the bandwidth and hence a better rate. But you do so simply by taking bandwidth from other downloaders. The overall supply of upload is unchange, it’s simply being shuffled around. If everybody does the same thing it results in overall slightly worse performance and you’re basically back where you started, but with a bunch of headaches tacked on.
So why does BitTorrent perform so well? Quite simply, because it does a better job of finding more places to do uploading. Any peer which is downloading is in general willing to upload as well, and their uplink is usually unutilized, so if you can get a peer to start uploading as soon as it starts downloading, and keep uploading as long as possible, and saturate its link while it’s uploading, then overall performance will be better. It doesn’t necessarily help to transfer over more connections, or make more different things available at the same time, or use error correcting codes. In fact, all of those are a complex tradeoff between benefits and costs, with the net result being that small amounts of them can help reliability and robustness, but in general it’s good to keep things simple and be polite to the network.
On the internet, the formula is bytes downloaded = bytes uploaded. It’s that simple.
Indeed it is.
jared@zeropaid.com
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On the internet, the formula is bytes downloaded = bytes uploaded
If only that were true
Actually, due to packets being lost or dropped between their source and destination, bytes downloaded < bytes uploaded.