BitTorrent creator slams Microsoft's methods

Writing in his blog about Microsoft's planned 'Avalanche' distributed file-sharing solution, Cohen said people were taking the product too seriously.

"I'd like to clarify that Avalanche is vapourware," he wrote. "It isn't a product which you can use or test with, it's a bunch of proposed algorithms. There isn't even a fleshed-out network protocol. The 'experiments' they've done are simulations."

"It's a bad idea to give too much weight to simulations, especially of something so hairy as real-world Internet behaviour."

Cohen came down heavily on the research paper that Microsoft used to introduce its technology. While the paper attempted to compare the Internet traffic methodology behind BitTorrent to Avalanche, Cohen said the analysis came up short.

"I think that paper is complete garbage," he wrote.

The developer said Microsoft had completely misunderstood the way BitTorrent operated. The paper quotes "the tit-for-tat approach used in the BitTorrent network" as an inspiration for parts of Avalanche's own operation. Under the approach, a peer-to-peer client will not upload any content to another client unless it has also received a certain amount of content in return.

Cohen said, however, this was a waste of time and had been discarded long ago.

"I can't fathom how they came up with this," he wrote. "Researching either the source code or the documentation on the BitTorrent Web site would have shown that the real choking algorithms work nothing like this."

"Either they just heard 'tit-for-tat' and just made this up, or they for some odd reason dredged up BitTorrent 1.0 and read the source of that." BitTorrent is currently at version 4.0.2.

Cohen went on to say that the 'tit-for-tat' approach was used when BitTorrent was still being developed, but that the first real-world test with only six connected machines showed that it did not work well.

"This gaffe alone makes their simulation completely worthless, but it isn't the only one," he wrote.

The BitTorrent creator said the paper misjudged the amount of peers each BitTorrent client will connect to while downloading. While the paper assumed that number was between four and six, he said in real life BitTorrent typically utilised between 30 and 50.

"In other words, intentionally or not, the simulation is completely rigged against BitTorrent," he concluded.

But Cohen didn't write off the paper entirely, saying despite its flaws, it could still be useful.

"Unfortunately, [the paper] is actually one of the better academic papers on BitTorrent, because it makes some attempt, however feeble, to do an apples to apples comparison," he said.