The P2P system
A simple model of the energy use of a P2P file sharing system
can be developed by assuming that the energy use of a computer
when uploading and downloading data is proportional to the
amount of data uploaded and downloaded. Since a peer downloads
every part of the file from some other peer, this assumption implies
that the energy use involved in downloading a file (i.e. a set of file
parts) is equal to twice the energy use of a single computer
downloading the file. Using a similar reasoning, but not accounting
for the energy use involved in receiving the file, the model used by
e.g. Nedevschi et al. (2008) expresses a direct proportional relationship
between the amount of data downloaded and the energy
use. Nedevschi et al. (2008) do not consider the electricity use of
the computers that they would have anyway just to be powered on.
This is however considered in our analysis. Since our study is a
descriptive attributional LCA, we needed a model that enabled us to