Standards (was [BitTorrent] Back to Merkle Hash Trees...)

Martin Nilsson yahoo at mani.user.lysator.liu.se
Wed Feb 9 00:21:57 EST 2005


Justin Cormack wrote:
> 
> Doing the maths, a 4G file with 64k pieces/chunks will have 64k of them,
> which means a bitmap is 8k, which is smaller than a request (64k) so
> thats not a huge transfer. you will get 64k have messages (worst case)
> which is 512k. These figures are per peer.
> 

Many times (seeds and recently started peers) it is also possible to 
apply high compression to the bitmap. Recursively divide the bitmap into 
two parts and make a binary tree. Then encode the the tree from the top with

00 - subtree all zeroes
01 - two nodes follows
10 - unencoded subtree follows
11 - subtree all ones

/Martin Nilsson



 
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