Microsoft's Holographic Bittorrent

I noticed an item on The Register that Microsoft has come up with an
improved replacement for Bittorrent.

Originally, peer-to-peer file sharing systems worked by allowing
individual files to be downloaded from computers in the system.

Then, Bittorrent took into account the asymmetrical nature of one of the
commonnest fast connections to the Internet, that which uses the cable
modem, and allowed simultaneous downloading of multiple pieces of the
same file from multiple sources.

Now, Microsoft came up with an idea to deal with one piece being hard to
obtain. I'm not sure it is really needed, since each source for a file
would have the whole file, and there would usually be more potential
sources than are used in a single transfer...

but the idea, as near as I can make it out from the description,
apparently works like this:

A source for a file would make available a particular linear combination
of the pieces into which the file is cut - and from independent linear
combinations of the files, the original file could be reconstructed.

If you know a+b and a-b, you can determine both a and b, since a =
((a+b) + (a-b)) / 2 and b = ((a+b) - (a-b)) / 2.

Using modulo 2^32 arithmetic on every four bytes of the file would allow
enough combinations.

It seems to use extra hard disk space, because one can't share the same
copy of a file as one uses.

John Savard
http://www.quadibloc.com/index.html
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Received on Thu Sep 29 21:44:46 2005