3442104
Node Isolation Model and Age-Based Neighbor Selection in Unstructured P2P Networks
Previous analytical studies of unstructured P2P resilience have assumed exponential user lifetimes and only considered age-independent neighbor replacement. In this paper, we overcome these limitations by introducing a general node-isolation model for heavy-tailed user lifetimes and arbitrary neighbor-selection algorithms. Using this model, we analyze two age-biased neighbor-selection strategies and show that they significantly improve the residual lifetimes of chosen users, which dramatically reduces the probability of user isolation and graph partitioning compared with uniform selection of neighbors. In fact, the second strategy based on random walks on age-proportional graphs demonstrates that, for lifetimes with infinite variance, the system monotonically increases its resilience as its age and size grow. Specifically, we show that the probability of isolation converges to zero as these two metrics tend to infinity. We finish the paper with simulations in finite-size graphs that demonstrate the effect of this result in practice.
3433910
Residual-Based Measurement of Peer and Link Lifetimes in Gnutella Networks
Existing methods of measuring lifetimes in P2P systems usually rely on the so-called create-based method (CBM), which divides a given observation window into two halves and samples users "created" in the first half every Delta time units until they die or the observation period ends. Despite its frequent use, this approach has no rigorous accuracy or overhead analysis in the literature. To shed more light on its performance, we flrst derive a model for CBM and show that small window size or large Delta may lead to highly inaccurate lifetime distributions. We then show that create-based sampling exhibits an inherent tradeoff between overhead and accuracy, which does not allow any fundamental improvement to the method. Instead, we propose a completely different approach for sampling user dynamics that keeps track of only residual lifetimes of peers and uses a simple renewal-process model to recover the actual lifetimes from the observed residuals. Our analysis indicates that for reasonably large systems, the proposed method can reduce bandwidth consumption by several orders of magnitude compared to prior approaches while simultaneously achieving higher accuracy. We finish the paper by implementing a two-tier Gnutella network crawler equipped with the proposed sampling method and obtain the distribution of ultrapeer lifetimes in a network of 6.4 million users and 60 million links. Our experimental results show that ultrapeer lifetimes are Pareto with shape a alpha ap 1.1; however, link lifetimes exhibit much lighter tails with alpha ap 1.9.
322407
IRLbot: Scaling to 6 billion pages and beyond
This article shares our experience in designing a Web crawler that can download billions of pages using a single-server implementation and models its performance. We first show that current crawling algorithms cannot effectively cope with the sheer volume of URLs generated in large crawls, highly branching spam, legitimate multimillion-page blog sites, and infinite loops created by server-side scripts. We then offer a set of techniques for dealing with these issues and test their performance in an implementation we call IRLbot. In our recent experiment that lasted 41 days, IRLbot running on a single server successfully crawled 6.3 billion valid HTML pages (7.6 billion connection requests) and sustained an average download rate of 319 mb/s (1,789 pages/s). Unlike our prior experiments with algorithms proposed in related work, this version of IRLbot did not experience any bottlenecks and successfully handled content from over 117 million hosts, parsed out 394 billion links, and discovered a subset of the Web graph with 41 billion unique nodes.
1958263
On zone-balancing of peer-to-peer networks: analysis of random node join
Balancing peer-to-peer graphs, including zone-size distributions, has recently become an important topic of peer-to-peer (P2P) research [1], [2], [6], [19], [31], [36]. To bring analytical understanding into the various peer-join mechanisms, we study how zone-balancing decisions made during the initial sampling of the peer space affect the resulting zone sizes and derive several asymptotic results for the maximum and minimum zone sizes that hold with high probability.
1202188
Load-Balancing Performance of Consistent Hashing: Asymptotic Analysis of Random Node Join
Balancing of structured peer-to-peer graphs, including their zone sizes, has recently become an important topic of distributed hash table (DHT) research. To bring analytical understanding into the various peer-join mechanisms based on consistent hashing, we study how zone-balancing decisions made during the initial sampling of the peer space affect the resulting zone sizes and derive several asymptotic bounds for the maximum and minimum zone sizes that hold with high probability. Several of our results contradict those of prior work and shed new light on the theoretical performance limitations of consistent hashing. We use simulations to verify our models and compare the performance of the various methods using the example of recently proposed de Bruijn DHTs.
1669034
Modeling Heterogeneous User Churn and Local Resilience of Unstructured P2P Networks
Previous analytical results on the resilience of unstructured P2P systems have not explicitly modeled heterogeneity of user churn (i.e., difference in online behavior) or the impact of in-degree on system resilience. To overcome these limitations, we introduce a generic model of heterogeneous user churn, derive the distribution of the various metrics observed in prior experimental studies (e.g., lifetime distribution of joining users, joint distribution of session time of alive peers, and residual lifetime of a randomly selected user), derive several closed-form results on the transient behavior of in-degree, and eventually obtain the joint in/out degree isolation probability as a simple extension of the out-degree model.
19093181
Threshold Proxy Signature Scheme with Strong Real-Time Efficiency
The threshold proxy signature scheme with strong real-time efficiency is proposed based on a trapdoor hash function and the sharing secret technology. In the scheme, the procedure of generating threshold proxy signature is performed in two phases. The off-line phase generates a threshold proxy pre-signature before the message to be signed is even known. The pre-signature is independent of the particular message to be signed and is stored for future in the on-line phase. While on-line phase generates quickly a threshold proxy signature using the pre-signature once the message to be signed is presented. The on-line phase is typically very fast and strong real-time efficiency since it only needs a few modular additions and multiplications and one round of communication among proxy signers. Furthermore, the scheme not only has strong real-time efficiency, but also withstands the conspiracy attack existed in the previous schemes and requires no trusted third party. The scheme is particularly useful for requiring the strong real-time efficiency and fully distributed networks such as electric wallet or smart cards etc.
2819336
Optimal harvesting problems for an age-dependent n-dimensional food chain model with diffusion
We investigate the optimal harvesting problems of an age-dependent n-dimensional food chain model with spartially structured, which is controlled by harvesting. The existence and uniqueness of solution for the system are proven using Banach fixed-point theorem. We establish existence result of optimal control and necessary optimality conditions.
14457115
General Method to Build Deterministic Small-World Networks Based on Cayley Graph
Many real-life networks, such as the WWW, biological realms, and social networks are small-world networks. Most previous researches on small-world networks have been based on probabilistic methods. In this paper, we present a general method by using Cayley graph to build deterministic small-world networks. We also analyze the cluster topology of the Cayley graph with small world properties by constructing its left Coset graph. This method has great value in constructing interconnection networks model and analyzing many other real network models.
25804073
Translational integrity and continuity: Personalized biomedical data integration
Translational research data are generated in multiple research domains from the bedside to experimental laboratories. These data are typically stored in heterogeneous databases, held by segregated research domains, and described with inconsistent terminologies. Such inconsistency and fragmentation of data significantly impedes the efficiency of tracking and analyzing human-centered records. To address this problem, we have developed a data repository and management system named TraM (http://tram.uchicago.edu), based on a domain ontology integrated entity relationship model. The TraM system has the flexibility to recruit dynamically evolving domain concepts and the ability to support data integration for a broad range of translational research. The web-based application interfaces of TraM allow curators to improve data quality and provide robust and user-friendly cross-domain query functions. In its current stage, TraM relies on a semi-automated mechanism to standardize and restructure source data for data integration and thus does not support real-time data application.
20162487
An efficient and scalable pairwise key pre-distribution scheme for sensor networks using deployment knowledge
Pairwise key establishment is a fundamental security service for sensor networks. However, establishing pairwise key in sensor networks is a challenging problem, particularly due to the resource constraints on sensor nodes and the threat of node compromises. On the other hand, adding new nodes to a sensor network is a fundamental requirement for their continuous operation over time, too. We analyze the weaknesses of security due to node capture when adding sensor nodes using key pre-distribution schemes with ''fixed'' key pools. In this paper, we propose a new approach, which separates the nodes into groups, the nodes in a group communicate with each other using pairwise keys pre-distributed, the communications between any two neighbor groups are accomplished also through pairwise keys, which is computed based on the pre-distributed Hash chain. We show that the performance (e.g. continuous connectivity, continuous network resilience against node capture and memory usage) of sensor networks can be substantially improved by using our scheme. The scheme and its detailed performance evaluation are presented.