On the Stability of Skype Super Nodes

The heart of skype services, one of the most ubiquitous P2P networks, is based on a set of super nodes. Choosing stable SNs is an important task, since it improves the whole performance and quality of the P2P network [1, 2]. In this paper we shed light on the life cycle of SNs using extensive data sets on Skype Super nodes, which were gathered over a period of 3 months. We then suggest how to choose a more stable SNs set.

The dynamic of nodes is inherent to the use of a computer, which is unplugged for some time or is mobile. Hence it is natural to predict that a Super Node would have multiple sessions correlated with the time the computer is up. Surprisingly, we show that 40% of the Super Nodes have only one session, with median residual life time of 1.75 days. These nodes also have a significantly shorter lifespan than Super Nodes that have multiple sessions, which have median residual life time of 67.5 days. We propose and give evidence that nodes with one session are nodes with dynamic IP addresses, and hence they have ended their life cycle due to a change of IP address. We show that the nodes with multiple sessions are mostly nodes with static IPs, and that choosing super nodes with static IPs would increase the availability and stability of the P2P network significantly.