Haiying Shen

Game-Theoretic Analysis of Cooperation Incentive Strategies in Mobile Ad Hoc Networks

In mobile ad hoc networks (MANETs), tasks are conducted based on the cooperation of nodes in the networks. However, since the nodes are usually constrained by limited computation resources, selfish nodes may refuse to be cooperative. Reputation systems and price-based systems are two main solutions to the node noncooperation problem. A reputation system evaluates node behaviors by reputation values and uses a reputation threshold to distinguish trustworthy nodes and untrustworthy nodes. A price-based system uses virtual cash to control the transactions of a packet forwarding service. Although these two kinds of systems have been widely used, very little research has been devoted to investigating the effectiveness of the node cooperation incentives provided by the systems. In this paper, we use game theory to analyze the cooperation incentives provided by these two systems and by a system with no cooperation incentive strategy. We find that the strategies of using a threshold to determine the trustworthiness of a node in the reputation system and of rewarding cooperative nodes in the price-based system may be manipulated by clever or wealthy but selfish nodes. Illumined by the investigation results, we propose and study an integrated system. Theoretical and simulation results show the superiority of the integrated system over an individual reputation system and a price-based system in terms of the effectiveness of cooperation incentives and selfish node detection.

Load Rebalancing for Distributed File Systems in Clouds

Distributed file systems are key building blocks for cloud computing applications based on the MapReduce programming paradigm. In such file systems, nodes simultaneously serve computing and storage functions; a file is partitioned into a number of chunks allocated in distinct nodes so that MapReduce tasks can be performed in parallel over the nodes. However, in a cloud computing environment, failure is the norm, and nodes may be upgraded, replaced, and added in the system. Files can also be dynamically created, deleted, and appended. This results in load imbalance in a distributed file system; that is, the file chunks are not distributed as uniformly as possible among the nodes. Emerging distributed file systems in production systems strongly depend on a central node for chunk reallocation. This dependence is clearly inadequate in a large-scale, failure-prone environment because the central load balancer is put under considerable workload that is linearly scaled with the system size, and may thus become the performance bottleneck and the single point of failure. In this paper, a fully distributed load rebalancing algorithm is presented to cope with the load imbalance problem. Our algorithm is compared against a centralized approach in a production system and a competing distributed solution presented in the literature. The simulation results indicate that our proposal is comparable with the existing centralized approach and considerably outperforms the prior distributed algorithm in terms of load imbalance factor, movement cost, and algorithmic overhead. The performance of our proposal implemented in the Hadoop distributed file system is further investigated in a cluster environment.

Locality-Aware and Churn-Resilient Load-Balancing Algorithms in Structured Peer-to-Peer Networks

Structured peer-to-peer overlay networks, like distributed hash tables (DHTs), map data items to the network based on a consistent hashing function. Such mapping for data distribution has an inherent load balance problem. Data redistribution algorithms based on randomized matching of heavily loaded nodes with light ones can deal with the dynamics of DHTs. However, they are unable to consider the proximity of the nodes simultaneously. There are other methods that rely on auxiliary networks to facilitate locality-aware load redistribution. Due to the cost of network construction and maintenance, the locality-aware algorithms can hardly work for DHTs with churn. This paper presents a locality-aware randomized load-balancing algorithm to deal with both the proximity and network churn at the same time. We introduce a factor of randomness in the probing of lightly loaded nodes in a range of proximity. We further improve the efficiency by allowing the probing of multiple candidates (d-way) at a time. Simulation results show the superiority of the locality-aware two-way randomized algorithm in comparison with other random or locality-aware algorithms. In DHTs with churn, it performs no worse than the best chum-resilient algorithm. It takes advantage of node capacity heterogeneity and achieves good load balance effectively even in a skewed distribution of items

Leveraging Social Networks for P2P Content-Based File Sharing in Disconnected MANETs

Current peer-to-peer (P2P) file sharing methods in mobile ad hoc networks (MANETs) can be classified into three groups: flooding-based, advertisement-based, and social contact-based. The first two groups of methods can easily have high overhead and low scalability. They are mainly developed for connected MANETs, in which end-to-end connectivity among nodes is ensured. The third group of methods adapts to the opportunistic nature of disconnected MANETs but fails to consider the social interests (i.e., contents) of mobile nodes, which can be exploited to improve the file searching efficiency. In this paper, we propose a P2P content-based file sharing system, namely SPOON, for disconnected MANETs. The system uses an interest extraction algorithm to derive a nodes interests from its files for content-based file searching. For efficient file searching, SPOON groups common-interest nodes that frequently meet with each other as communities. It takes advantage of node mobility by designating stable nodes, which have the most frequent contact with community members, as community coordinators for intracommunity searching, and highly mobile nodes that visit other communities frequently as community ambassadors for intercommunity searching. An interest-oriented file searching scheme is proposed for high file searching efficiency. Additional strategies for file prefetching, querying-completion, and loop-prevention, and node churn consideration are discussed to further enhance the file searching efficiency. We first tested our system on the GENI Orbit testbed with a real trace and then conducted event-driven experiment with two real traces and NS2 simulation with simulated disconnected and connected MANET scenarios. The test results show that our system significantly lowers transmission cost and improves file searching success rate compared to current methods.

An Efficient and Adaptive Decentralized File Replication Algorithm in P2P File Sharing Systems

In peer-to-peer file sharing systems, file replication technology is widely used to reduce hot spots and improve file query efficiency. Most current file replication methods replicate files in all nodes or two end points on a client-server query path. However, these methods either have low effectiveness or come at a cost of high overhead. File replication in server side enhances replica hit rate, hence, lookup efficiency but produces overloaded nodes and cannot significantly reduce query path length. File replication in client side could greatly reduce query path length, but cannot guarantee high replica hit rate to fully utilize replicas. Though replication along query path solves these problems, it comes at a high cost of overhead due to more replicas and produces underutilized replicas. This paper presents an Efficient and Adaptive Decentralized (EAD) file replication algorithm that achieves high query efficiency and high replica utilization at a significantly low cost. EAD enhances the utilization of file replicas by selecting query traffic hubs and frequent requesters as replica nodes, and dynamically adapting to nonuniform and time-varying file popularity and node interest. Unlike current methods, EAD creates and deletes replicas in a decentralized self-adaptive manner while guarantees high replica utilization. Theoretical analysis shows the high performance of EAD. Simulation results demonstrate the efficiency and effectiveness of EAD in comparison with other approaches in both static and dynamic environments. It dramatically reduces the overhead of file replication, and yields significant improvements on the efficiency and effectiveness of file replication in terms of query efficiency, replica hit rate, and overloaded nodes reduction.

A Review of Communication, Driver Characteristics, and Controls Aspects of Cooperative Adaptive Cruise Control (CACC)

Cooperative adaptive cruise control (CACC) systems have the potential to increase traffic throughput by allowing smaller headway between vehicles and moving vehicles safely in a platoon at a harmonized speed. CACC systems have been attracting significant attention from both academia and industry since connectivity between vehicles will become mandatory for new vehicles in the USA in the near future. In this paper, we review three basic and important aspects of CACC systems: communications, driver characteristics, and controls to identify the most challenging issues for their real-world deployment. Different routing protocols that support the data communication requirements between vehicles in the CACC platoon are reviewed. Promising and suitable protocols are identified. Driver characteristics related issues, such as how to keep drivers engaged in driving tasks during CACC operations, are discussed. To achieve mass acceptance, the control design needs to depict real-world traffic variability such as communication effects, driver behavior, and traffic composition. Thus, this paper also discusses the issues that existing CACC control modules face when considering close to ideal driving conditions.

Consolidating Complementary VMs with Spatial/Temporal-awareness in Cloud Datacenters

In cloud datacenters, effective resource provisioning is needed to maximize energy efficiency and utilization of cloud resources while guaranteeing the Service Level Agreement (SLA) for tenants. Previous resource provisioning strategies either allocate physical resources to virtual machines (VMs) based on static VM resource demands or dynamically handle the variations in VM resource requirements through live VM migrations. However, the former fail to maximize energy efficiency and resource utilization while the latter produce high migration overhead. To handle these problems, we propose an initial VM allocation mechanism that consolidates complementary VMs with spatial/temporal-awareness. Complementary VMs are the VMs whose total demand of each resource dimension (in the spatial space) nearly reaches their hosts capacity during VM lifetime period (in the temporal space). Based on our observation of the existence of VM resource utilization patterns, the mechanism predicts the lifetime resource utilization patterns of short-term VMs or periodical resource utilization patterns of long-term VMs. Based on the predicted patterns, it coordinates the requirements of different resources and consolidates complementary VMs in the same physical machine (PM). This mechanism reduces the number of PMs needed to provide VM service hence increases energy efficiency and resource utilization and also reduces the number of VM migrations and SLA violations. Simulation based on two real traces and real-world testbed experiments show that our initial VM allocation mechanism significantly reduces the number of PMs used, SLA violations and VM migrations of the previous resource provisioning strategies.

SocialTube: P2P-assisted Video Sharing in Online Social Networks

Video sharing has been an increasingly popular application in online social networks (OSNs). However, its sustainable development is severely hindered by the intrinsic limit of the client/server architecture deployed in current OSN video systems, which is not only costly in terms of server bandwidth and storage but also not scalable with the soaring amount of users and video content. The peer-assisted Video-on-Demand (VoD) technique, in which participating peers assist the server in delivering video content, has been proposed recently. Unfortunately, videos can only be disseminated through friends in OSNs. Therefore, current VoD works that explore clustering nodes with similar interests or close location for high performance are suboptimal, if not entirely inapplicable, in OSNs. Based on our long-term real-world measurement of over 1,000,000 users and 2,500 videos on Facebook, we propose SocialTube, a novel peer-assisted video sharing system that explores social relationship, interest similarity, and physical location between peers in OSNs. Specifically, SocialTube incorporates four algorithms: a social network (SN)-based P2P overlay construction algorithm, an SN-based chunk prefetching algorithm, chunk delivery, and scheduling algorithm, and a buffer management algorithm. Experimental results from a prototype on PlanetLab and an event-driven simulator show that SocialTube can improve the quality of user experience and system scalability over current P2P VoD techniques.

SOAP: A Social network Aided Personalized and effective spam filter to clean your e-mail box

The explosive growth of unsolicited emails has prompted the development of numerous spam filtering techniques. A Bayesian spam filter is superior to a static keywordbased spam filter because it can continuously evolve to tackle new spam by learning keywords in new spam emails. However, Bayesian spam filters can be easily poisoned by avoiding spam keywords and adding many innocuous keywords in the emails. In addition, they need a significant amount of time to adapt to a new spam based on user feedback. Moreover, few current spam filters exploit social networks to assist spam detection. In order to develop an accurate and user-friendly spam filter, in this paper, we propose a SOcial network Aided Personalized and effective spam filter (SOAP). Unlike previous filters that focus on parsing keywords (e.g, Bayesian filter) or building blacklists, SOAP exploits the social relationship among email correspondents to detect the spam adaptively and automatically. SOAP integrates three components into the basic Bayesian filter: social closeness-based spam filtering, social interest-based spam filtering, and adaptive trust management. We evaluate performance of SOAP based on the trace data from Facebook. Experimental results show that SOAP can greatly improve the performance of Bayesian spam filters in terms of the accuracy, attack-resilience and efficiency of spam detection. We also find that the performance of Bayesian spam filters is the lower bound of SOAP.

A Distributed Spatial-Temporal Similarity Data Storage Scheme in Wireless Sensor Networks

Since centralized data storage and search schemes often lead to high overhead and latency, distributed data-centric storage becomes a preferable approach in large-scale wireless sensor networks (WSNs). However, most of existing distributed methods lack optimization for spatial-temporal search to query events occurred in a certain geographical area and a certain time period. Furthermore, for data search routing, most methods rely on locating systems (e.g., GPS), which consume high energy. This paper proposes a distributed spatial-temporal Similarity Data Storage (SDS) scheme. SDS provides efficient spatial-temporal and similarity data searching service, and is applicable for both static and dynamic WSNs. It disseminates event data in such a way that the distance between WSN neighborhoods represents the similarity of data stored in them. In addition, SDS carpooling routing algorithm efficiently routes messages without the aid of GPS. Theoretical and experimental results show that SDS yields significant improvements on the efficiency of data querying compared with existing approaches, and obtains stable performance in dynamic environments.