Have compression (was Re: Standards (was [BitTorrent] Back to Merkle Hash Trees...))

Olaf van der Spek OvdSpek at LIACS.NL
Wed Feb 9 05:54:07 EST 2005

Justin Cormack wrote:
> Olavs protcol lets you request in 32k chunks (and verify) but you can only
> send have messages in this predetermined size set by whover made the
> torrent. Lets junk the fixed piece size, and see what the options are.

How often do I have to point out the chunk_have mssage?

> Here is one suggestion
> Lets change the have (and request etc) messages to look like
> uint32_t clen
> uint8_t message_type
> uint8_t log
> uint32_t piece

Should response messages still match request messages or are you allowed 
to send only part of the requested range?

> Now this doesnt buy us anything if we send a have message after each chunk,
> but we now have the ability to dynamically vary piece size. First thing we
> think about is how large a piece can we request in one go. Clearly if we
> request really big pieces (the whole file!) we send fewer have messages but
> increase the latency of them.

What's the definition of latency here?

> First thing we notice is that we dont have to send messages at the same rate
> to all peers. If we are choking them, we dont need to send any messages
> until the point we unchoke, so we can batch them. Another strategy is to send
> have messages for rare pieces immediately to the peers that dont have them,

What's rare for you doesn't have to be rare for somebody else.

> while you coalesce common ones.

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