[bittorrent] about transfer rate...

Elliott Mitchell ehem at m5p.com
Sun Jan 15 19:38:07 EST 2006

Is this perhaps being overthought? The client might merely be reporting
its interaction with the peer. Your client _knows_ how many PIECE
messages it sends, and _knows_ how many PIECE messages is receives.
Nothing special needed, though it doesn't give a complete picture.

>From: Joris Guisson <joris.guisson at gmail.com>
> As for the download rate that's pretty simple :
> If you received 20 HAVE s in the last 10 seconds, and the chunks are
> 512K large, the peer will have downloaded 10 MB in the last 10
> seconds, so their average download speed over that period is 1 MB/s

This might be used in an attempt to provide a more complete picture, but
this depends on behavior present in the mainline and many clients that
the protocol does not require. Specifically it requires the peer to send
HAVE messages for every peer for every block received.

In particular there is no requirement to advertise possession of pieces.
Generally doing so allows you to trade and therefore download more, but
there are circumstances where a client could choose not to do this. In
particular if a peer is known to already have a piece, then advertising
possession of that piece doesn't gain you anything. So you would have a
phenomenon that as you start to posses more pieces, you have to guess
about unadvertised pieces.

The final guess is that your peers' upload:download ratios are quite
likely to be similar to your upload:download ratio. They're /likely/ to
connect to a similar number of seeds, similar number of vanilla peers,
and overall a just plain similar mix of peers. Again, imperfect, but
allows you to make reasonable guesses.

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