TR-IIS-08-012    Fulltext

Abstract

Instant Messaging (IM) has emerged as a popular communication service over the Internet. One of the themes of IM systems is to provide a presence directory that carries information on user’s presence or absence to his/her friends. In this paper, we present new presence directory architecture and give a comparison of existing presence directories. We first introduce the distributed buddy-list search problem.We then present P2Dir, a distributed peer-to-peer presence directory protocol to address this problem. For each newly arriving user, the protocol is used to search for network presence of his/her buddies and also to notify them on his/her presence. P2Dir organizes directory servers into a 2-hop P2P overlay for efficient buddy searching. Moreover, P2Dir leverages the breadth-first search algorithm and a onehop caching strategy to achieve small constant search latency on average. We measure the performance of our P2Dir system, in terms of search cost and search satisfaction, where search cost is defined as total number of messages incurred among the directories upon the arrival of a user, and search satisfaction is defined as the time it takes to search for the newly arriving user’s buddy list and to notify presence of the newly arriving user to his/her buddies. We evaluate the performance of our P2Dir system in terms of search cost and search satisfaction through simulations, and compare it with a mesh-based presence protocol. The results show that our P2Dir achieves performance gains in search cost without sacrificing search satisfaction.