We propose and evaluate a mobile, peer-to-peer information retrieval system. Such a system can, for example, support medical care in a disaster by allowing access to a large collections of medical literature. In our system, documents in a collection are replicated in an overlapping manner at mobile peers. This provides resilience in the face of node failures, malicious attacks, and network partitions. We show that our design manages the randomness of node mobility. Although nodes contact only direct neighbors (who change frequently) and do not use any ad hoc routing, the system maintains good IR performance. This makes our design applicable to mobility situations where routing partitions are common. Our evaluation shows that our scheme provides significant savings in network costs, and increased access to information over ad-hoc routing-based approaches; nodes in our system require only a modest amount of additional storage on average.

Choosing the best-performing server for a particular client from a group of replicated proxies is a difficult task. We offer a novel, two-step technique for server selection that chooses a small subset of five servers, and isolates testing to that subset for ten days. We present an empirical evaluation of both our method and previously proposed metrics based on traces to 193 commercial proxies. We show that our technique performs better than any of the other metrics we studied -often one to two seconds better for a one-megabyte file-while requiring considerably less work over time. Metrics such as round-trip time and tests using small files usually select servers that are two to three times worse than the best server. Network-layer metrics such as minimizing router and autonomous system count poorly predict which server provides the best performance. These metrics often select servers with transfer times four to six times that of the best-performing server.