Re: [p2prg] New version of p2prg-mythbustering

[Ray.Bellis at nominet.org.uk]

> Well, no, if the content was locally available (i.e.
one seeder
> existed), but the local leecher downloaded it from outside, the total
> cost of the traffic generated by the two peers would amount to £220
as
> the seeder would just be serving some other off-net leecher (and thus
> costing another £110).

I was thinking more of a trivial example of two leechers
on-net, and one seeder off-net.

Using a 10:1 cost ratio between backhaul and transit,
and assuming a cost of "1 unit" for the cost of transferring
that data over the transit.

If both leechers download everything from the seeder:

  = 2 clients * (backhaul + transit)
  = 2 * (10 + 1)
  = 22 units

If each leacher downloads exactly half of the data
from the seeder, and the remaining half from the other leacher (assuming
non-overlapping fragments):

  =   2 clients * 0.5 * (backhaul + transit)
    + 2 clients * (up+down) + 0.5 * backhaul
     [*]
  =  (2 * 5.5) + (2 * 2 * 5)
  =  33 units

so it appears that the on-net leeching costs 50% more
than two downloads from off-net.

Ray

[*] I think I've done this right - each leecher downloads
half of the file from the other leecher, but the ISP has to pay for it
in both directions.