Locating content in decentralized peer-to-peer systems is a challenging problem. Gnutella, a popular file-sharing application, relies on flooding queries to all peers. Although flooding is simple and robust, it is not scalable. In this paper, we explore how to retain the simplicity of Gnutella, while addressing its inherent weakness: scalability. We propose a content location solution in which peers loosely organize themselves into an interest-based structure on top of the existing Gnutella network. Our approach exploits a simple, yet powerful principle called interest-based locality, which posits that if a peer has a particular piece of content that one is interested in, it is very likely that it will have other items that one is interested in as well. When using our algorithm, called interest-based shortcuts, a significant amount of flooding can be avoided, making Gnutella a more competitive solution. In addition, shortcuts are modular and can be used to improve the performance of other content location mechanisms including distributed hash table schemes. We demonstrate the existence of interest-based locality in five diverse traces of content distribution applications, two of which are traces of popular peer-to-peer file-sharing applications. Simulation results show that interest-based shortcuts often resolve queries quickly in one peer-to-peer hop, while reducing the total load in the system by a factor of 3 to 7.

Abstract-While Packet Fair Queueing (PFQ) algorithms provide both bounded delay and fairness in wired networks, they cannot be applied directly to wireless networks. The key difficulty is that in wireless networks sessions can experience location-dependent channel errors. This may lead to situations in which a session receives significantly less service than it is supposed to, while another receives more. This results in large discrepancies between the sessions' virtual times, making it difficult to provide both delay-guarantees and fairness simultaneously.Our contribution is twofold. First, we identify a set of properties, called Channel-condition Independent Fair (CIF), that a Packet Fair Queueing algorithm should have in a wireless environment: (1) delay and throughput guarantees for error-free sessions, (2) long term fairness for error sessions, (3) short term fairness for error-free sessions, and (4) graceful degradation for sessions that have received excess service. Second, we present a methodology for adapting PFQ algorithms for wireless networks and we apply this methodology to derive a novel algorithm based on Start-time Fair Queueing, called Channel-condition Independent packet Fair Queueing (CIF-Q), that achieves all the above properties. To evaluate the algorithm we provide both theoretical analysis and simulation results.

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Fluids of molecules or particles interacting through dipole forces describe polar liquids and colloidal suspensions such as ferroQuids and electrorheological fluids. Phase diagrams for systems with strong dipolar coupling are not precisely known. Possible liquid state phase transitions include phase separation and spontaneous polarization. We present a set of generic phase diagrams for the Huid states of dipolar spheres and spheroids, focusing on the interplay of polarization and phase separation.

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