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Recently researchers use skyline techniques to optimize service selection procedure, where they can filter those low-quality web services from the large amount of candidates and return a much smaller high-quality service set. The skycube concept is adopted for quickly responding to the skyline queries with different combinations of Quality of Web Service (QoWS) parameters. As the skycube computation is quite time-consuming, it is a compelling challenge to accelerate this procedure. However, the current solutions usually have a number of redundant computations which will significantly affect the efficiency. To address such drawbacks, after an in-depth analysis of skycube computation procedure, we introduce a partial skycube, which only consists of the skylines with frequently used combinations of QoWS. Then the computational relationships between the skyline on one subspace and its parent-space are studied. Based on the relationships, we develop ${\sf {ParCube}}$ ParCube algorithm to speedup partial skycube computation by reusing the intermediate comparison results. Meanwhile, at the execution phase, ${\sf {ParCube}}$ ParCube can be further optimized with parallel execution mode and optimized scheduling strategy. Finally, we evaluate the efficiency and scalability of ${\sf {ParCube}}$ ParCube on both single machine and cluster environment. The results show that ${\sf {ParCube}}$ ParCube can efficiently compute partial skycube and scale well in cluster environment.

In cloud computing, it is crucial to maintain service continuity, while power outage is one of the most common and serious threats. To improve the resilience of cloud against power outage, a service provider usually deploys emergency energy supply (e.g., UPSs and generators) in a data center. When a power outage at a data center happens, the cloud service provider needs to make the operation decision on which subset of VMs to keep running and which servers to host such VMs to minimize its loss (or maximize its profit) using the emergency energy supply while the selected VMs are running in the affected data center until they are finished, migrated to other data centers, or normal power supply of the affected data center has been restored. No prior research has theoretically studied such a cloud service continuity problem under power outage. In this paper, we tackle this challenge and investigate the cloud service continuity problem. Specifically, we consider that a profit is associated with maintaining the continuity of a service, denoted as service continuity profit . Based on that we first formulate an optimization problem that aims to maximize the total profit subject to energy constrains. After showing the hardness of the problem, we focus on the design of approximation algorithms for solving the problem, where we consider two practical cases. In the first one with sufficient number of servers for re-provisioning, we develop a constant approximation algorithm of which the worst-case performance approaches the optimal solution within a constant factor ( $\approx$ ≈ 4.5-6.4). In the second one, we consider the general case with limited number of servers, and we develop an approximation algorithm with an approximation ratio of around 5.7-8. By combining these two algorithms together, we can achieve both good worst-case performance and average performance. Simulation results demonstrate the efficiency in terms of maximizing the service continuity profit of the proposed algorithms.

Cardinality estimation is the task of determining the number of distinct elements (or the cardinality) in a data stream, under a stringent constraint that the input data stream can be scanned by just one single pass. This is a fundamental problem with many practical applications, such as traffic monitoring of high-speed networks and query optimization of Internet-scale database. To solve the problem, we propose an algorithm named HLL-TailCut, which implements the estimation standard error $1.0 / \sqrt {m}$ using the memory units of four or three bits each, whose cost is much smaller than the five-bit memory units used by HyperLogLog, the best previously known cardinality estimator. This makes it possible to reduce the memory cost of HyperLogLog by 20%~45%. For example, when the target estimation error is 1.1%, state-of-the-art HyperLogLog needs 5.6 kilobytes memory. By contrast, our new algorithm only needs 3 kilobytes memory consumption for attaining the same accuracy. Additionally, our algorithm is able to support the estimation of very large stream cardinalities, even on the Tera and Peta scale.

For large-scale online social networks such as Facebook and Twitter, network analysis often uses graph queries to extract network information. Because of the work and memory required, usually such queries are performed in a distributed manner. However, most existing distributed graph computation systems optimize for offline graph analysis rather than online graph queries. The problem with this approach is that graph query tasks then must transfer a large volume of data and interactively answer queries within a short time frame. To resolve this, we propose a novel data-locality-aware task scheduling algorithm that optimizes interactive distributed graph queries. The scheduling algorithm jointly considers data placement and graph topology to reduce data transfer costs. After implementing the scheduling algorithm in a real-world distributed graph computation system, we evaluate the task scheduler’s effectiveness through simulations and real-life social graph queries. Results show that our scheduler reduces the querying time by one order of magnitude.

Radio-frequency identification (RFID) technology has been widely adopted in various industries and people’s daily lives. This paper studies a fundamental function of spatial-temporal joint cardinality estimation in distributed RFID systems. It allows a user to make queries over multiple tag sets that are present at different locations and times in a distributed tagged system. It estimates the joint cardinalities of those tag sets with bounded error. This function has many potential applications for tracking product flows in large warehouses and distributed logistics networks. The prior art is either limited to jointly analyzing only two tag sets or is designed for a relative accuracy model, which may cause unbounded time cost. Addressing these limitations, we propose a novel design of the joint cardinality estimation function with two major components. The first component is to record snapshots of the tag sets in a system at different locations and periodically, in a time-efficient way. The second component is to develop accurate estimators that extract the joint cardinalities of chosen tag sets based on their snapshots, with a bounded error that can be set arbitrarily small. We formally analyze the bias and variance of the estimators, and we develop a method for setting their optimal system parameters. The simulation results show that, under predefined accuracy requirements, our new solution reduces time cost by multiple folds when compared with the existing work.

Transmission is crucial for big data analysis and learning in industrial Internet of Things (IoT) systems. To transmit data with limited energy is a challenge. This paper studies the problem of data transmission in energy harvesting systems with capacitor to supply energy where the energy receiving rate varies over time. The energy receiving rate is slower when the capacitor receives more energy. Based on this characteristic, we study the problem of how to transmit more data when the energy receiving time is not continuous. Given many packets that arrive at different time instances, there is a tradeoff between transmitting the packet right now or saving the energy to transmit the future arriving packets. We formalize two types of problems. The first one is how to minimize the total completion time when there is enough energy to transmit all the packets. The second one is how to transmit as many packets as possible when the energy is not enough to transmit all the packets. For the first problem, we give a $1+\alpha$ approximation offline algorithm when all the information of the packets and the energy receiving periods is known in advance, and a $\max \lbrace 2,\beta \rbrace$ competitive ratio online algorithm where the information is not known in advance. For the second problem, we study three cases and give a $6+\lceil \frac{h}{b/R} \rceil$ approximation offline algorithm for the general situation. We also prove that there does not exit a constant competitive ratio online algorithm.

Networks have become increasingly important to model many complex systems. This powerful representation has been employed in different tasks of artificial intelligence including machine learning, expert and intelligent systems. Link prediction, a branch of network pattern recognition, is the most fundamental and essential problem for complex network analysis. However, most existing link-prediction methods only consider a network’s topology structures, and in doing so, these methods miss the opportunity to use nodes’ attribute information. We present a combined approach here that uses nodes’ attribute information and topology structure to direct link prediction. First, we propose a discriminative feature combinations selection method. Specifically, we present a novel mathematics inference to detail discriminative feature combinations. Second, based on the selected feature combinations, we aggregate the network, and further compute each feature combination’s contributing degree to the link’s formation, called the strength of feature combination. Third, we apply discriminative feature combinations into a local random walk model; in particular, we compute and redistribute the random walk particle’s transfer probability in terms of each feature combination’s strength, which makes the transfer probability depend on feature combinations satisfied by each node’s edges. Finally, we predict links in complex networks based on the improved random walk model. Experimental results on real-life complex network datasets demonstrate that, compared to other baseline methods, using discriminative feature combinations and topology structures in tandem strengthens prediction performance remarkably.

Radio frequency identification (RFID) technology has rich applications in cyber-physical systems, such as warehouse management and supply chain control. Often in practice, tags are attached to objects belonging to different groups, which may be different product types/manufacturers in a warehouse or different book categories in a library. As RFID technology evolves from single-group to multiple-group systems, there arise several interesting problems. One of them is to identify the popular groups, whose numbers of tags are above a pre-defined threshold. Another is to estimate arbitrary moments of the group size distribution, such as sum, variance, and entropy for the sizes of all groups. In this paper, we consider a new problem which is to estimate all these statistical metrics simultaneously in a time-efficient manner without collecting any tag IDs. We solve this problem by a protocol named generic moment estimator (GME), which allows the tradeoff between estimation accuracy and time cost. According to the results of our theoretical analysis and simulation studies, this GME protocol is several times or even orders of magnitude more efficient than a baseline protocol that takes a random sample of tag groups to estimate each group size.

Radiative wireless power transfer (WPT) is a promising technique to power wireless devices’ transmission. In a resource-limited device, receiving energy and transmitting data cannot operate at the same time because they share the same spectrum or hardware. This paper studies the problem for a wireless device to decide when to harvest energy, when to deliver data, and what transmission rate to use. Distinct from the most existing works, we focus on delay minimization in transmitting a sequence of data packets over a point-to-point channel, which is critical for time-sensitive applications. Since the battery is capacitated, the device must repeatedly switch between harvesting energy and transmitting data. For the offline case where packet information is known before scheduling, a surprising result is discovered that for all (energy receiving and data transmitting) cycles, except the last one, the optimal transmission rate should be a constant which is called the wOPT rate . Based on this discovery, the offline delay minimization problem is optimally solved. For the online case where packets arrive dynamically without prior information, we propose a simple online algorithm: using the wOPT rate to transmit whenever both energy and data are ready. It is proved to be 1.16-competitive if the battery is initially empty, namely, its delay is less than 1.16 times the offline optimal delay for any given packet set. When the battery is with arbitrary initial energy, simulation results show that the performance is near optimal. The discovery of the wOPT rate reveals an essential property of WPT and is expected to be significant in solving other related problems.

Electrocardiogram (ECG) data classification is a hot research area for its application in medical information processing. However, insufficient data, privacy preserve, and local deployment are still challenging difficulties. To address these problems, a novel personalized federated learning method for ECG classification is proposed in this paper. First, a global model is trained with federated learning framework on multiple local data clients. Then, we use the global model and private data to train the local model. To reduce the feature inconsistency between global and private local data and for better fitting the private local data, a novel ”feature alignment” module is devised to guarantee the uniformity, which contains two parts, global alignment and local alignment, respectively. For global alignment, the graph metric of batch data is used to constrain the dissimilarity between features generated by the global model and local model. For local alignment, triplet loss is adopted to increase discriminative ability for local private data. Comprehensive experiments on our collected dataset are evaluated. The results show that the proposed method can be better adapted to local data and exhibit superior ability of generalization.

Wireless power transfer (WPT) is a recently developed technique to perfectly address the energy problem for smart city sensors that do not have a readily wired power supply. In a radio-frequency-powered wireless communication system, sensors first harvest energy via the radio-frequency WPT, and then, transmit sensed data to the receiver. The “harvest-then-transmit” protocol is used to coordinate the two operations, in which we wish to optimally decide when to harvest energy, when to transmit data, and what transmission rate should be used such that the data are maximally transmitted. Unlike existing works, we assumed that the wireless transferred power is dynamically changing, instead of being constant, which is more realistic in green smart city applications, e.g., Industry 4.0 workshop, smart transportation, and smart buildings, where environments are continuously changing, so the wireless transferred power is affected dynamically. In this paper, we present an optimal scheduling algorithm for the offline case where the varying WPT is known in advance. Based on the optimal principles learned from the offline case, we have designed an efficient online algorithm. Finally, we report our simulation results that demonstrate that our online scheduling algorithm can adaptively and efficiently achieve high data throughput.

TC is a promising network computing paradigm that offers an efficient way to make lightweight terminals more powerful, convenient, and secure. TC's execution model separates data storage and application execution, letting terminals load applications from TC servers on demand via the Internet. With this approach, the network's performance significantly affects the TC applications' performance. To enhance TC applications' performance, existing research typically deploys many cache servers on the Internet. However, such caching techniques are not ideal in a mobile environment, where the wireless networks that mobile terminals use for Internet access are expensive and have limited bandwidth. To address this problem, we propose COAST, a cooperative storage framework for MTC. Based on a deviceto- device data-sharing technique, COAST enables a mobile terminal to fetch applications from nearby terminals without accessing the Internet. In this article, we introduce COAST's design, explore the opportunities and challenges of cooperative storage in MTC environments, and identify future research directions.

For many practical applications, it is a fundamental problem to estimate the flow cardinalities over big network data consisting of numerous flows (especially a large quantity of mouse flows mixed with a small number of elephant flows, whose cardinalities follow a power-law distribution). Traditionally the research on this problem focused on using a small amount of memory to estimate each flow’s cardinality from a large range (up to ${10}^{{9}}$ ). However, although the memory needed for each individual flow has been greatly compressed, when there is an extremely large number of flows, the overall memory demand can still be very high, exceeding the availability under some important scenarios, such as implementing online measurement modules in network processors using only on-chip cache memory. In this paper, instead of allocating a separated data structure (called estimator ) for each flow, we take a different path by viewing all the flows together as a whole: Each flow is allocated with a virtual estimator, and these virtual estimators share a common memory space. We discover that sharing at the multi-bit register level is superior than sharing at the bit level. We propose a unified framework of virtual estimators that allows us to apply the idea of sharing to an array of cardinality estimation solutions, e.g., HyperLogLog and PCSA, achieving far better memory efficiency than the best existing work. Our experiment shows that the new solution can work in a tight memory space of less than 1 bit per flow or even one tenth of a bit per flow — a quest that has never been realized before.

Radio frequency identification (RFID) technology has been widely used in Applications, such as inventory control, object tracking, and supply chain management. In this domain, an important research problem is called RFID cardinality estimation , which focuses on estimating the number of tags in a certain area covered by one or multiple readers. This paper extends the research in both temporal and spatial dimensions to provide much richer information about the dynamics of distributed RFID systems. Specifically, we focus on estimating the cardinalities of the intersection/differences/union of two arbitrary tag sets (called joint properties for short) that exist in different spatial or temporal domains. With many practical applications, there is, however, little prior work on this problem. We will propose a joint RFID estimation protocol that supports adaptive snapshot construction. Given the snapshots of any two tag sets, although their lengths may be very different depending on the sizes of tag sets they encode, we design a way to combine their information and more importantly, derive closed-form formulas to use the combined information and estimate the joint properties of the two tag sets, with an accuracy that can be arbitrarily set. By formal analysis, we also determine the optimal system parameters that minimize the execution time of taking snapshots, under the constraints of a given accuracy requirement. We have performed extensive simulations, and the results show that our protocol can reduce the execution time by multiple folds, as compared with the best alternative approach in literature.

Web-scale knowledge graphs containing billions of entities are common nowadays. Querying these graphs can be modeled as a subgraph matching problem. Since knowledge graphs are incomplete and noisy in nature, it is important to discover answers matching exactly as well as answers similar to queries. Existing graph matching algorithms usually use graph indices to accelerate query processing. For billion-node graphs, it may be infeasible to build the graph indices due to the amount of work and the memory/storage required. In this paper, we propose an efficient algorithm for finding the best $k$ answers for a given query without precomputing graph indices. An answer’s quality is measured by a matching score that is computed online. To accelerate query processing, we propose a novel technique for bounding the matching scores during the computation. By using bounds, the low quality answers can be efficiently pruned. The bounding technique can be implemented in a distributed environment, allowing our approach to efficiently query web-scale knowledge graphs. We evaluate the effectiveness and the efficiency of our approach on real-world datasets. The result shows that our bounding technique can reduce the running time up to two orders of magnitude comparing to an approach without using bounds.

Incomplete microdata, i.e., microdata with missing value, is very common in real-world datasets. However, existing anonymization techniques, which were developed for complete datasets, suffer from serious information loss on incomplete microdata, due to the missing value pollution. In this paper, we propose a framework for utility enhanced anonymization of incomplete microdata to address this issue. First, we study the properties of missing value pollution on generalization. Guided by these properties, we develop two top-down anonymization algorithms to preserve data utility on incomplete microdata. Extensive experiments on real-world datasets show that our techniques outperform the state-of-the-art techniques in terms of information loss and missing value pollution.

In crowdsourcing markets, a requester announces a task and calls for contribution from potential participants. With strategic participants, the requester needs to reward the participants to introduce the incentives of participation. However, it is natural to ask whether it is worth introducing incentives if the total payment for eliciting incentives is too high. This paper addresses such a fundamental concern by designing a frugal mechanism with minimum payment used to procure the total amount of service contributions demanded. We design two mechanisms to provide the incentives of participation while minimizing the payment used by the requester. We first propose a frugal auction-based mechanism, which stimulates participants to truthfully report their information. We theoretically prove that the payment used is not more than the optimal cost (with no incentive considered) plus a bounded additive. We then design a Stackelberg-game-based mechanism, in which the requester fixes a certain total payment at the very beginning so as to encourage the participants to compete for it and participate in the task. We verify the existence of a unique Nash equilibrium (NE) and develop a novel algorithm to find the NE, as well as the optimal payment to extract the NE. Our simulation results show that the payment used in these mechanisms is close to the optimal solution with no incentive considered, while the extra payment caused by introducing truthfulness in auction-based mechanism is about twice that of the NE in Stakelberg-game-based mechanism.

Cybercrime is significantly growing as the development of internet technology. To mitigate this issue, the law enforcement adopts network surveillance technology to track a suspect and derive the online profile. However, the traditional network surveillance using the single-device tracking method can only acquire part of a suspect’s online activities. With the emergence of different types of devices (e.g., personal computers, mobile phones, and smart wearable devices) in the mobile edge computing (MEC) environment, one suspect can employ multiple devices to launch a cybercrime. In this paper, we investigate a novel cross-device tracking approach which is able to correlate one suspect’s different devices so as to help the law enforcement monitor a suspect’s online activities more comprehensively. Our approach is based on the network traffic analysis of instant messaging (IM) applications, which are typical commercial service providers (CSPs) in the MEC environment. We notice a new habit of using IM applications, that is, one individual logs in the same account on multiple devices. This habit brings about devices’ receiving sync messages, which can be utilized to correlate devices. We choose five popular apps (i.e., WhatsApp, Facebook Messenger, WeChat, QQ, and Skype) to prove our approach’s effectiveness. The experimental results show that our approach can identify IM messages with high F1-scores (e.g., QQ’s PC message is 0.966, and QQ’s phone message is 0.924) and achieve an average correlating accuracy of 89.58% of five apps in an 8-people experiment, with the fastest correlation speed achieved in 100 s.

Energy harvesting communication system enables energy to be dynamically harvested from natural resources and stored in capacitated batteries to be used for future data transmission. In such a system, the amount of future energy to harvest is uncertain and the battery capacity is limited. As a consequence, battery overflow and energy dropping may happen, causing energy underutilization. To maximize the data throughput by using the energy efficiently, a rate-adaptive transmission schedule must address the trade-off between a high-rate transmission which avoids energy overflow and a low-rate transmission which avoids energy shortage. In this paper, we study an online throughput maximization problem without knowing future information. To the best of our knowledge, this is the first work studying the fully-online transmission rate scheduling problem for battery-capacitated energy harvesting communication systems. We consider the problem under two models of the communication channel, a static channel model that assumes the channel status is stable, and a fading channel model that assumes the channel status varies. For the former, we develop an online algorithm that approximates the offline optimal solution within a constant factor for all possible inputs. For the latter, that the channel gains vary in range $[h_{min},h_{max}]$ , we propose an online algorithm with a proven $\Theta (\log (\frac{h_{max}}{h_{min}}))$ -competitive ratio. Our simulation results further validate the efficiency of the proposed online algorithms.

Recent developments in networking have spurred the emergence of time-sensitive applications such as Web search, social networks, and the Industrial Internet. TCP, as the core networking protocol, implements reliable packet delivery for these applications. However, TCP isn't specifically optimized for timely packet delivery, so it has poor performance for time-sensitive scenarios. To counter this, the network research community has worked extensively on standards for reducing TCP's latency. Explicit Congestion Notification (ECN) is an extension to TCP/IP that's recommended for realizing low-latency TCP. This article surveys IETF standardization efforts for ECN-based solutions, and also proposes suggestions and future directions on this topic.

In a participatory sensing system, data sensed from smartphone users are shared with the general public who requests data through submitting tasks. When multiple tasks request the data from a mobile user, the mobile user can make a transmission schedule to achieve the balance between the amount of data transmitted and energy consumption. Intuitively, reducing the amount of data transmitted by making use of data sharing between the tasks can save the energy consumption. However, due to the convexity of rate-power function for rate-adaptive transmitting devices, a schedule purely minimizing the amount of data transmitted may not always be the optimal one minimizing the energy consumption. Thus, there exists a tradeoff between the amount of data transmitted and energy consumption. This paper formulates the problem as a bi-objective optimization problem to simultaneously minimize the amount of data transmitted and the energy consumption. Two task models are studied, first-in-first-out (FIFO) task model and arbitrary deadline (AD) task model, respectively. We first provide optimal algorithms for the off-line case. We then study the online case where requests arrive dynamically without prior information. For FIFO tasks, we develop an online algorithm that is $O(\ln L)$ -competitive with respect to both the amount of data transmitted and energy consumption, where $L$ is the longest length of the time duration of the tasks. For AD tasks, we devise an online algorithm that is $O(\ln ^{2} L)$ -competitive with respect to both the amount of data transmitted and energy consumption. Our simulation results validate the efficiency of our online algorithms.

MapReduce is undoubtedly the most popular framework for large-scale processing and analysis of vast data sets in clusters of machines. To facilitate the easier use of MapReduce, SQL-like declarative languages and SQL-to-MapReduce translators have attracted increasing attentions recently. The SQL-to-MapReduce translator can automatically generate the MapReduce jobflow for each SQL query submitted by users, which significantly simplifies the interfacing between users and systems. Although a plethora of translators have been developed, the auto-generated MapReduce programs still suffered from extremely inefficiency. In this paper, we attempt to address this challenge by developing a novel Cost-Aware Translator (CAT). CAT has two notable features. First, it defines two intra-SQL correlations: Generalized Job Flow Correlation (GJFC) and Input Correlation (IC), based on which a set of looser merging rules are introduced. Thus, both Top-Down (TD) and Bottom-Up (BU) merging strategies are proposed and integrated into CAT simultaneously. Second, it adopts a cost estimation model for MapReduce jobflows to guide the selection of a more efficient MapReduce jobflows auto-generated by TD and BU merging strategies. Finally, comparative experiments on TPC-H benchmark demonstrate the effectiveness and scalability of CAT.

With the popularization and development of cloud computing, lots of scientific computing applications are conducted in cloud environments. However, current application scenario of scientific computing is also becoming increasingly dynamic and complicated, such as unpredictable submission times of jobs, different priorities of jobs, deadlines and budget constraints of executing jobs. Thus, how to perform scientific computing efficiently in cloud has become an urgent problem. To address this problem, we design an elastic resource provisioning and task scheduling mechanism to perform scientific workflow jobs in cloud. The goal of this mechanism is to complete as many high-priority workflow jobs as possible under budget and deadline constraints. This mechanism consists of four steps: job preprocessing, job admission control, elastic resource provisioning and task scheduling. We perform the evaluation with four kinds of real scientific workflow jobs under different budget constraints. We also consider the uncertainties of task runtime estimations, provisioning delays, and failures in evaluation. The results show that in most cases our mechanism achieves a better performance than other mechanisms. In addition, the uncertainties of task runtime estimations, VM provisioning delays, and task failures do not have major impact on the mechanism's performance.

Tor is a popular low-latency anonymous communication system. It is, however, currently abused in various ways. Tor exit routers are frequently troubled by administrative and legal complaints. To gain an insight into such abuse, we designed and implemented a novel system, TorWard, for the discovery and the systematic study of malicious traffic over Tor. The system can avoid legal and administrative complaints, and allows the investigation to be performed in a sensitive environment such as a university campus. An intrusion detection system (IDS) is used to discover and classify malicious traffic. We performed comprehensive analysis and extensive real-world experiments to validate the feasibility and the effectiveness of TorWard. Our results show that around 10% Tor traffic can trigger IDS alerts. Malicious traffic includes P2P traffic, malware traffic (e.g., botnet traffic), denial-of-service attack traffic, spam, and others. Around 200 known malwares have been identified. To mitigate the abuse of Tor, we implemented a defense system, which processes IDS alerts, tears down, and blocks suspect connections. To facilitate forensic traceback of malicious traffic, we implemented a dual-tone multi-frequency signaling-based approach to correlate botnet traffic at Tor entry routers and that at exit routers. We carried out theoretical analysis and extensive real-world experiments to validate the feasibility and the effectiveness of TorWard for discovery, blocking, and traceback of malicious traffic.

Tor is a famous anonymous communication system for preserving users' online privacy. It supports TCP applications and packs upper-layer application data into encrypted equal-sized cells with onion routing to hide private information of users. However, we note that the current Tor design cannot conceal certain application behaviors. For example, P2P applications usually upload and download files simultaneously, and this behavioral feature is also kept in Tor traffic. Motivated by this observation, we investigate a new attack against Tor, application classification attack, which can recognize application types from Tor traffic. An attacker first carefully selects some flow features such as burst volumes and directions to represent the application behaviors and takes advantage of some efficient machine-learning algorithm e.g., Profile Hidden Markov Model to model different types of applications. Then he or she can use these established models to classify target's Tor traffic and infer its application type. We have implemented the application classification attack on Tor using parallel computing, and our experiments validate the feasibility and effectiveness of the attack. We argue that the disclosure of application type information is a serious threat to Tor users' anonymity because it can be used to reduce the anonymity set and facilitate other attacks. We also present guidelines to defend against application classification attack. Copyright © 2015 John Wiley & Sons, Ltd.

The use of Big Data and the development of cloud computing have led to greater dependence on data-intensive services. Each service may actually request or create a large amount of data sets. The scope, number, and complexity of data-intensive services are all set to soar in the future. To compose these services will be more challenging. Issues of autonomy, scalability, adaptability, and robustness, become difficult to resolve. Bio-inspired algorithms can overcome the new challenging requirements of data-intensive service provision. It is useful for the provision of data-intensive services to explore key features and mechanisms of biological systems and accordingly to add biological mechanisms to services. In this paper, we will discuss single-objective and multi-objective data-intensive service provision problems based on bio-inspired algorithms. Further, we will propose an ant-inspired negotiation approach. Finally, this paper points out future research topics. Copyright © 2015 John Wiley & Sons, Ltd.

In the big data era, scientific workflow exhibits the characteristics of data intensity and becomes increasingly popular in scientific domains. Efficient scheduling of data-intensive scientific workflow in a multiple datacenter DC environment has been a long-standing challenge. Most of previous work on data-intensive scientific workflow scheduling primarily focused on the optimization of reducing the volumes of data transfer between workflow tasks. In this paper, novel scheduling strategies for the execution of data-intensive scientific workflow in multi-DC environment are proposed aiming at the optimization of the overall data transfer time. A novel DC selection approach is proposed to minimize the number of DCs having enough storage capacity for the execution of scientific workflow as well as optimized inter-DC network bandwidth for efficient data transfer between workflow tasks. A k-means clustering-based data placement strategy is adopted to intelligently place the initial data of scientific workflow thereby reducing the volume of initial data transfer between different DCs. A multilevel task replication scheduling strategy is invented to reduce the volumes of intermediate data transfer between DCs during the runtime of the scientific workflow. Simulations spanning a broad range of scientific workflow and multi-DC settings are performed in order to verify the proposed approaches. The numerical results show that our combined scheduling strategy significantly reduces the overall data transfer time and data transfer volume when scientific workflow is scheduled in multi-DC environment. Copyright © 2015 John Wiley & Sons, Ltd.

Tor is a well-known low-latency anonymous communication system that is able to bypass the Internet censorship. However, publicly announced Tor routers are being blocked by various parties. To counter the censorship blocking, Tor introduced non-public bridges as the first-hop relay into its core network. In this paper, we investigated the effectiveness of two categories of bridge-discovery approaches: 1) enumerating bridges from bridge HTTPS and email servers, and 2) inferring bridges by malicious Tor middle routers. Large-scale real-world experiments were conducted and validated our theoretic findings. We discovered 2365 Tor bridges through the two enumeration approaches and 2369 bridges by only one Tor middle router in 14 days. Our study shows that the bridge discovery based on malicious middle routers is simple, efficient, and effective to discover bridges with little overhead. We also discussed issues related to bridge discovery and mechanisms to counter the malicious bridge discovery.

Large data centers are usually built to support increasing computational and data storage demand of growing global business and industry, which consume an enormous amount of energy, at a huge cost to both business and the environment. However, much of that energy is wasted to maintain excess service capacity during periods of low load. In this paper, we investigate the problem of "right-sizing" data center for energy-efficiency through virtualization which allows consolidation of workloads into smaller number of servers while dynamically powering off the idle ones. In view of the dynamic nature of data centers, we propose a stochastic model based on Queueing theory to capture the main characteristics. Solving this model, we notice that there exists a tradeoff between the energy consumption and performance. We hereby develop a BFGS based algorithm to optimize the tradeoff by searching for the optimal system parameter values for the data center operators to "right-size" the data centers. We implement our Stochastic Right-sizing Model (SRM) and deploy it in the real-world cloud data center. Experiments with two real-world workload traces show that SRM can significantly reduce the energy consumption while maintaining high performance. A Stochastic Right-sizing Model(SRM) based on Queueing theory is proposed.A BFGS based algorithm is proposed to achieve energy-efficiency.SRM is implemented with open-source cloud platform OpenStack.

Scientific workflow structured as Parallel Task Graphs (PTG) exhibits both data and task parallelism, and arises in scientific as well as in industrial domains. Efficient scheduling of such workflow on a multicluster platform has been a longstanding challenge. Most of previous work on PTG scheduling primarily focused on dedicated multicluster. In this paper, a novel scheduling algorithm known as the Moldable Task Duplication (MTD) is applied to non-dedicated heterogeneous multicluster platform with advance reservations. A novel method for the calculation of dynamic critical path that handles the availability fluctuation of multicluster and the moldability of scientific workflow’s data-parallel tasks is proposed. A moldable task duplication strategy with migration of pre-duplicated predecessor tasks is developed to fully exploit the flexibility of data-parallel tasks. Simulations spanning a broad range of scientific workflow and multicluster platform settings are performed in order to verify the proposed approach. The numerical results show that MTD can achieve better average PTG makespan than previous methods in

The explosion of enormous sources of digital data has led to greater dependence on data-intensive services. Applications based on data-intensive services have become one of the most challenging applications in cloud computing. The service provision, and in particular service composition, will face new challenges as the services and data grow. In this paper, we will evaluate an ant colony system to resolve the multi-objective data-intensive service composition problem. The algorithm for a multi-objective context will get a set of Pareto-optimal solutions considering two objectives at the same time: the total cost and the total execution time of a composite service.

To fulfill global requirements for network security and privacy, anonymous communication systems have been extensively investigated and deployed over the world to provide anonymous communication services for users. Nonetheless, diverse de-anonymizing techniques have been proposed to compromise anonymity and impose a severe threat to anonymous communication systems. In this article, we classify the existing de-anonymizing techniques and provide an overview of these techniques. In addition, corresponding countermeasures are studied to mitigate the risks posed by these de-anonymizing techniques.

This paper presents an optimal rate scheduling algorithm called Truncation for an energy-harvesting enabled wireless transmitter to transmit a set of dynamically arrived packets with minimum transmission energy. Distinct from existing works, we allow packets to have individual delay constraints, which is the most general model ever assumed but is very much desired to guarantee per-application quality-of-service (QoS). Moreover, we restrict the allowable rates to a set of discrete values, which is more practical and required in many real applications. As the first achievement, we obtain an optimal offline algorithm, which assumes the rate is continuously adjustable. Then, we propose a general framework that transforms any algorithm using the continuous-rate model into an algorithm using only discrete-rates, while preserving the optimality as long as the optimality holds for convex rate-power functions. It is possible that the harvested energy is insufficient to guarantee all packets to meet their deadlines. Should this occur, maximizing throughput with the limited available energy becomes the goal to achieve. Our Truncation algorithm is able to identify this case and produces a schedule that guarantees maximum throughput, if packets share a common deadline. Furthermore, based on the optimal offline algorithms, an efficient online algorithm is designed which has been shown by simulations to produce near optimal results.

Given a rate adaptive wireless transmitter, a challenging problem is to design a rate control policy for it such that the energy consumption is minimized at transmitting a set of dynamically arrived packets with arbitrary individual deadlines. In a decade, researches have partially made progress on this topic. A latest work offers an optimal algorithm that allows packets to have arbitrary deadlines but requires them to follow the order they arrive. This paper first presents the Densest Interval First (DIF) policy which repeatedly locates the densest data interval and determines its transmission rate. This policy is proved to be optimal for the most general model that allows arbitrary arrival times as well as arbitrary deadlines. Then, this paper presents a simple EDF (earliest deadline first) algorithm to actually schedule the transmission time for each packet. It is proved that the EDF always guarantees every packet to complete transmission before its deadline with minimum energy consumption which is computed and required by DIF. Finally, this paper also proposes a novel online policy named Density Guided Cooling (DGC) policy which models Newton's Law of Cooling. Simulations show that online DGC policy constantly produces a rate scheduling that on average consumes energy within 110% of the minimum value obtained by the offline DIF.

Server farms generally consume an enormous amount of energy, which not only increases the running cost but also simultaneously enhances their greenhouse gas emissions. One way to improve the energy efficiency in server farms is dynamical powering on/off servers. However, this method suffers from many setup time to turn the servers back on, which would have a negative impact on a job's response time and waste yet additional energy. This situation is further exacerbated by the unreliability of the servers, which has become the norm in today's server farms. In this paper, we investigate the impact of dynamical powering on/off servers on energy and performance in a typical server farm environment. Prior work has analyzed similar models for a single server, but no analytical results are known for multiservers. We mainly use the matrix geometric method to analyze this model, and system performance measures are explicitly developed in terms of computable forms. An energy-performance trade-off model is derived to determine the optimal management policy for the server farms. Finally, we discuss some extensions of our model to show its robustness and to point out avenues for future research. Numerical examples are provided at several points throughout the paper to illustrate the correctness of our analysis results and to validate the optimization approach. Copyright © 2014 John Wiley & Sons, Ltd.

Online aggregation (OLA) is an attractive sampling-based technology to response aggregation queries by an approximate estimate to the final result, with the confidence interval becomes tighter over time. It has been built into the MapReduce-based cloud system for big data analytics, which allows users to monitor the query progress, and save money by killing the computation early once sufficient accuracy has been obtained. However, there is a serious limitation that restricts the performance of OLA that is the sharing issue of multiple OLA queries processing. Note that, in the original MapReduce paradigm, each query is processed independently without considering the potential sharing opportunities, leading to two major unnecessary additional execution costs: (1) the large redundant I/O cost, and (2) the replicative statistical computation cost. To eliminate such additional execution cost and improve the overall performance, we present online aggregation with two-level sharing strategy in cloud (OATS) based on MapReduce framework in this paper to effectively support online aggregation for large scale concurrent query processing in skewed data distribution. In the first-level sharing, we propose a sample buffer management mechanism to share the sampling opportunities among multiple OLA queries to reduce redundant I/O cost. While in the second-level sharing, we propose a heuristic algorithm (with a good scalability for large input) for the statistical computation to share partial statistics calculation to decrease the number of final aggregation operations, reducing the statistical computation cost. Based on such two-level sharing strategy, we have implemented OATS in Hadoop and conducted an extensive experiments study on the TPC-H benchmark for skewed data distribution. Our results demonstrate the efficiency and effectiveness of OATS.

In this paper, we present a study on the anonymity of Anonymizer, a well-known commercial anonymous communication system. We discovered the architecture of Anonymizer and found that the size of web packets in the Anonymizer network can be very dynamic at the client. Motivated by this finding, we investigated a class of novel packet size-based covert channel attacks against Anonymizer. The attacker between a website and the Anonymizer server can manipulate the web packet size and embed secret signal symbols into the target traffic. An accomplice at the user side can sniff the traffic and recognize the secret signal. In this way, the anonymity provided by Anonymizer is compromised. We developed intelligent and robust algorithms to cope with the packet size distortion incurred by Anonymizer and Internet. We developed techniques to make the attack harder to detect: 1) We pick up right packets of web objects to manipulate to preserve the regularity of the TCP packet size dynamics, which can be measured by the Hurst parameter; 2) We adopt the Monte Carlo sampling technique to preserve the distribution of the web packet size despite manipulation. We have implemented the attack over Anonymizer and conducted extensive analytical and experimental evaluations. It is observed that the attack is highly efficient and requires only tens of packets to compromise the anonymous web surfing via Anonymizer. The experimental results are consistent with our theoretical analysis.