The4th InternationalWorkshoponPeer-to-PeerSystemswasheld atCornellon February 24th and 25th 2005.The IPTPS workshopcontinued to bring together researchersand practitioners from a variety of disciplines, including networking, theory,databases,security,andscienti?ccomputing. Theydescribedexperim- tal ?ndings, discussed challenges, and presented novel techniques. We received 123 submissions. Submissions were limited to 6 pages, one page morethanin previousyears.ThesubmissionswerereviewedbyaProgramC- mitteeconsistingof18internationalexpertsfromacademiaandindustry.Aftera bidding process,each committee member was assigned 20 papers to review, g- erating 3 reviews for each paper. Controversial papers were assigned additional reviewers.Thepaperswerethenrankedbasedonoriginality,technicalmerit,and topical relevance,aswell asthe likelihood that the ideas expressedwouldlead to insightful technical discussions at the workshop. The program chairs suggested a program which was extensively discussed and revised by the entire committee to produce the ?nal program. We accepted 24 papers, which were organized into 8 sessions: Security and Incentives, Search, Multicast, Overlay Algorithms, Empirical Studies, and N- work Locality, and two sessions on miscellaneous topics. Authors revised their submissions for a preproceedings distributed at the workshop. After the wo- shop, the authors revised their papers once more for the proceedings before you.

Inhalt
Workshop Report.- Workshop Report.- Security and Incentives.- A Self-repairing Peer-to-Peer System Resilient to Dynamic Adversarial Churn.- A First Look at Peer-to-Peer Worms: Threats and Defenses.- A Taxonomy of Rational Attacks.- Search.- Brushwood: Distributed Trees in Peer-to-Peer Systems.- Arpeggio: Metadata Searching and Content Sharing with Chord.- OverCite: A Cooperative Digital Research Library.- Miscellaneous.- NetProfiler: Profiling Wide-Area Networks Using Peer Cooperation.- A Statistical Theory of Chord Under Churn.- Peering Peer-to-Peer Providers.- Multicast.- The Impact of Heterogeneous Bandwidth Constraints on DHT-Based Multicast Protocols.- Chainsaw: Eliminating Trees from Overlay Multicast.- FeedTree: Sharing Web Micronews with Peer-to-Peer Event Notification.- Overlay Algorithms.- Hybrid Overlay Structure Based on Random Walks.- Quickly Routing Searches Without Having to Move Content.- Practical Locality-Awareness for Large Scale Information Sharing.- Empirical Studies.- An Empirical Study of Free-Riding Behavior in the Maze P2P File-Sharing System.- Clustering in P2P Exchanges and Consequences on Performances.- The Bittorrent P2P File-Sharing System: Measurements and Analysis.- Miscellaneous.- Dynamic Load Balancing in Distributed Hash Tables.- High Availability in DHTs: Erasure Coding vs. Replication.- Conservation vs. Consensus in Peer-to-Peer Preservation Systems.- Exploiting Network Locality.- Locality Prediction for Oblivious Clients.- Impact of Neighbor Selection on Performance and Resilience of Structured P2P Networks.- Evaluating DHT-Based Service Placement for Stream-Based Overlays.