[BitTorrent] BT2 & hash trees

Elliott Mitchell ehem at m5p.com
Mon Jul 19 01:40:36 EDT 2004


>From: Gregorio Roper <gregorio at gmx.li>

> Is there any chance of using a block size of 1024 bytes for the hash tree, since it 
> completely removes any limitations imposed by the block size, even for small files and 
> it's also the block size recommended by THEX[1] which is used by several p2p networks that 
> could then be used as a backup in case the tracker fails.

1024 would make sense if the protocol could address blocks that small.
As only a few discrete block sizes make sense (somewhere in the 16KB or
32KB range), trying to limit the block# to be a byte makes sense. If a
bit is allocated to indicate block size, you can address 128 blocks,
which means a minimum of 2K blocks for 256KB pieces (and then the issue
of whether to allow selectible larger block sizes comes up).

> I didn't find any comment on how the pieces of a torrent will be addressed. If I 
> understood correctly that BT2 is supposed to allow cross-trading, may I suggest that the 
> pieces be addressed similar to: <file root hash><log2(pieceSize) or level in hash 
> tree><pieceNum>.

And once again addressing by the hash of the piece, shrinks this down to
one element, a single hash.


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