  In this paper, we model the cost incurred by each peer participating in a
peer-to-peer network. Such a cost model allows to gauge potential disincentives
for peers to collaborate, and provides a measure of the ``total cost'' of a
network, which is a possible benchmark to distinguish between proposals. We
characterize the cost imposed on a node as a function of the experienced load
and the node connectivity, and show how our model applies to a few proposed
routing geometries for distributed hash tables (DHTs). We further outline a
number of open questions this research has raised.
