The Necessity of Supernodes

Peer-to-Peer (P2P) networks have grown to such a massive scale that performing an efficient search in the network is non-trivial. Systems such as Gnutella [1] were initially plagued with scalability problems as the number of users grew into the tens of thousands. As the number of users has now climbed into the millions, system designers have resorted to the use of supernodes to address scalability issues and to perform more efficient searches. While the use of supernodes has become commonplace in unstructured P2P networks, no theoretical bounds on search time have been established. We analyze search time and show that supernodes are required for efficient search. We also formulate the optimal reduction in search time that can be achieved by using supernodes and show a construction where search time of O(loglogn) is realized.