Mitigating unfairness in locality-aware peer-to-peer networks

Locality-awareness is considered as a promising approach to increase the efficiency of content distribution by peer-to-peer (P2P) networks, e.g., BitTorrent. It is intended to reduce the inter-domain traffic which is costly for Internet service providers (ISPs) and to simultaneously increase the performance from the viewpoint of the P2P users, i.e., to shorten download times. This win-win situation should be achieved by a preferred exchange of information between peers which are located closely to each other in the underlying network topology. A set of studies shows that these approaches can lead to a win-win situation under certain conditions, and to a win-no lose situation in most cases. However, the scenarios used mostly assume homogeneous peer distributions. This is not the case in practice according to recent measurement studies. Therefore, we extend previous work in this paper by studying scenarios with real-life, skewed peer distributions. We show that even a win-no lose situation is difficult to achieve under those conditions and that the actual impact for a specific peer heavily depends on the used locality-aware peer selection and the specific scenario. This contradicts the principle of economic traffic management (ETM) which aims for a solution where all involved players benefit and consequently have an incentive to adopt locality-awareness. Therefore, we propose and evaluate refinements of current proposals, achieving that all users of P2P networks can be sure that their application performance is not reduced. This mitigates the unfairness introduced by current proposals which is a key requirement for a broad acceptance of the concept of locality-awareness in the user community of P2P networks. Copyright c © 2010 John Wiley & Sons, Ltd.