Evolution of superpeer topologies - An analytical perspective

In superpeer based networks, resourceful peers (having high bandwidth and computational resources) are discovered through the process of bootstrapping, whereby they get upgraded to superpeers. However, bootstrapping is influenced by several factors like limitation on the maximum number of connections a peer can have due to bandwidth constraints, limitation on the availability of information of existing peers due to cache size constraints and also by the attachment policy of the newly arriving peers to the resourceful peers. In this paper, we derive closed form equations that model the effect of these factors on superpeer related topological properties of the networks. Based on the model, we show that existing bootstrapping protocols can lead to a situation where only a small fraction of the resourceful peers gets converted to superpeers, i.e., a large fraction of them remain underutilized; we later validate this statement using real Gnutella snapshots. We observe that as a node attachment policy, newly arriving peers must use a combination of random and preferential attachment strategy so as to ensure proper utilization of the resourceful peers. We also show that the cache parameters must also be suitably tuned so as to increase the fraction of superpeers in the network. Finally, we show that in real Gnutella networks the degree distribution generated using our models suitably fits the corresponding empirical values.