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Tue, 21 Jun 2005
Subject: Saddened by Bram Cohen
Tis sad that Cohen doesn't quite get the benefits of using something like Reed Solomon codes with Bittorrent. The primary benefit is to reduce the rarity of blocks and to allow for an effecient resolution of the 99% problem where peers are searching the network for the last block. You might ask how does this reduce rarity? Well imagine our seeder is spitting out blocks in a linear order, after it is done the data blocks it starts to spit out error code blocks. Basically a leecher just need to wait til he has enough data and or code blocks to rebuild the file (the size of the file). If these error blocks are in the network other leechers can grab them and once enough are accumulated rebuild their file. This reduces rarity because each error block is not localized, it is related to the whole, so it doesn't really matter what combination we use. (I'm not saying avalanche uses this). The point is that suddenly we have a bunch of blocks which by working together act as other data blocks, then effectively reduces the rarity of data because you no longer need to ask for just that one block, you can be taking code blocks while you are searching for relevant data blocks. So you send code blocks out when there is extra bandwidth, but from the seeder point of view it doesn't matter which blocks they send out, if they send out code tho it allows people to rebuild easier. We are effectively adding more blocks to the network almost increasing the rarity of other blocks but this counteracted by the fact the error code blocks are not locallized and can rebuild other blocks. |
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