On the effect of peer online times on the lookup service of Chord and Kademlia P2P systems

P2P systems can be used to provide a wide spectrum of traditional and novel applications. These systems are built around distributed hash tables (DHTs) that allow them to achieve efficient storage and retrieval of resources. A DHT is a data structure whose storage is distributed among network peers. Chord and Kademlia are two relevant examples of such DHTs. A limiting factor for the proper operation of P2P networks is the aggregate effect of peer arrivals and departures. This phenomenon is called churn and it negatively affects the quality of the services provided by DHTs. The lookup service, for instance, is a function that receives a resource ID as the input and determines the pointer to the holder of such resource. This service may fail if the nodes that store parts of a DHT leave the network. In this work we study the performance of the lookup service of Chord and Kademlia in simulation scenarios with different peer online times. We found that, by making use of long-lived peers in the network structure, Kademlia achieves better performance than Chord. Our results suggest that this benefit is obtained even with a low fraction of long-lived peers.