Challenges of DHT Design for a Public Communications System
David A. Bryan, Marcia Zangrilli, Bruce B. Lowekamp · 2006
Communications systems, encompassing VoIP, IM, and other personal media, present different challenges for P2P environments than other P2P applications. In particular, reliable communication implies that each resource (person) is unique and must be reliably located, without false negatives. The system must function in the presence of NATs, which create non-transitive connectivity, and must be resilient against DoS attacks that attempt to disrupt its routing properties or DoS a particular person. We have designed and implemented a P2P communications system using an extension of the Chord algorithm as a resource location service. In this paper we present the design tradeoffs necessary to meet the requirements of a reliable communications system. In particular, the practical issues of non-transitive routing, NATs used by residential endpoints, and the prevention of DoS attacks are more critical than strict performance metrics in selecting DHT identifier, topology, and routing algorithms. Where a central authority exists, certificates can be stored in the overlay and allow more efficient DHT algorithms to be used, but securing an open network with NATs requires appropriate Node-ID, replica placement, and routing algorithms.