[BitTorrent] Re: bt2 protocol features

Stephen Thomas flabdablet at yahoo.com
Thu Jun 10 18:07:58 EDT 2004


--- In BitTorrent at yahoogroups.com, John Hoffman <theshadow at s...> wrote:
> I'd have to disagree; the overhead in requesting by offset would be 4 
> bytes (2^32*16384 = 64 terabyte max torrent size), while requesting by 
> hash would be 20 bytes.

That's true, provided you do your requests one at a time.  But if you
request several blocks at once from a given peer (the normal case, I
would think, for small blocks) you can compress the requests by using
bit strings.  You send one hash to identify the parent block
*containing* the hashes you're actually requesting, and a string of
bits saying which of those you want.

This works because both ends will already be in possession of the
parent block.

Even if you only do this one level deep, you could request up to 60
blocks with 220 bits of request.






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