Joni Montemayor
Digital Fountain
They call it Midnight Madness: A big file, like the trailer for The Lord of the Rings, becomes popular, and the download frenzy clogs pipelines worldwide. Why? Standard file servers chop up the data into packets and deliver them over TCP, which uses back-and-forth chatter to make sure lost pieces are replaced. The same process repeats each time someone new clicks the Download Now button.
Digital Fountain has a clever alternative for that: Its Download Fountain and Streaming Fountain servers generate metapackets that can be lost without consequence. A free, downloadable plug-in collects the necessary number of metapackets and reconstructs a perfect copy of the file. Any packets will do - the server just needs 105% of the volume of the original. Because packet loss doesn't matter, the servers use UDP, the quick-and-dirty user datagram protocol that dispenses with resends. Free from having to repeat itself and address recipients individually, one Fountain server does the work of scores of TCP packet pushers.
Metapackets rely on math like this: if x, y and z are regular packets - slices of the original file - metapackets contain the values of random linear expressions such as x + y, x + y + z, where + represents the logical operator XOR. Because equal values combined with XOR cancel each other out, you can XOR compound expressions together to derive x, y and z.
Digital Fountain testers include Sprint, Sony and Cisco, but the company could be vulnerable to freeware based on tornado codes, a prior technology that's well known in academia. Tornado codes are less flexible than Digital FOuntain formulas, and they demand more clientside computation power, but Fountain Servers start at a hefty $40,000.
Resources:
Wired Magazine, June 2001 Edition
www.digitalfountain.com
www.serverwatch.com/img/transfount/
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