Mingjun Xiao

Community-Aware Opportunistic Routing in Mobile Social Networks

Mobile social networks (MSNs) are a kind of delay tolerant network that consists of lots of mobile nodes with social characteristics. Recently, many social-aware algorithms have been proposed to address routing problems in MSNs. However, these algorithms tend to forward messages to the nodes with locally optimal social characteristics, and thus cannot achieve the optimal performance. In this paper, we propose a distributed optimal Community-Aware Opportunistic Routing (CAOR) algorithm. Our main contributions are that we propose a home-aware community model, whereby we turn an MSN into a network that only includes community homes. We prove that, in the network of community homes, we can still compute the minimum expected delivery delays of nodes through a reverse Dijkstra algorithm and achieve the optimal opportunistic routing performance. Since the number of communities is far less than the number of nodes in magnitude, the computational cost and maintenance cost of contact information are greatly reduced. We demonstrate how our algorithm significantly outperforms the previous ones through extensive simulations, based on a real MSN trace and a synthetic MSN trace.

FACTS: A Framework for Fault-Tolerant Composition of Transactional Web Services

Along with the standardization of Web services composition language and the widespread acceptance of composition technologies, Web services composition is becoming an efficient and cost-effective way to develop modern business applications. As Web services are inherently unreliable, how to deliver reliable Web services composition over unreliable Web services is a significant and challenging problem. In this paper, we propose FACTS, a framework for fault-tolerant composition of transactional Web services. We identify a set of high-level exception handling strategies and a new taxonomy of transactional Web services to devise a fault-tolerant mechanism that combines exception handling and transaction techniques. We also devise a specification module and a verification module to assist service designers to construct fault-handling logic conveniently and correctly. Furthermore, we design an implementation module to automatically implement fault-handling logic in WS-BPEL. A case study demonstrates the viability of our framework and experimental results show that FACTS can improve fault tolerance of composite services with acceptable overheads.

Homing spread: Community home-based multi-copy routing in mobile social networks

A mobile social network (MSN) is a special delay tolerant network (DTN) composed of mobile nodes with social characteristics. Mobile nodes in MSNs generally visit community homes frequently, while other locations are visited less frequently. We propose a novel zero-knowledge MSN routing algorithm, homing spread (HS). The community homes have a higher priority to spread messages into the network. Theoretical analysis shows that the proposed algorithm can spread a given number of message copies in an optimal way when the inter-meeting times between any two nodes and between a node and a community home follow exponential distributions. We also calculate the expected delivery delay of HS. In addition, extensive simulations are conducted. Results show that community homes are important factors in efficient message spreading. By using homes to spread messages faster, HS achieves a better performance than existing zero-knowledge MSN routing algorithms, including Epidemic, with a given number of copies, and Spray&Wait.

A Declarative Approach to Enhancing the Reliability of BPEL Processes

Currently, BPEL is the de-facto standard for the Web service composition. Because Web services are autonomous and loosely coupled, BPEL processes are susceptible to a wide variety of faults. However, BPEL only provides limited constructs for handling faults, which makes fault handling a time-consuming and error-prone task. In this paper, we propose a declarative approach to enhancing the reliability of BPEL processes. Our solution specifies fault handling logic through a set of event- condition-action (ECA) rules which build on an extensible set of fault-tolerant patterns. These ECA rules are integrated with normal business logic before deployment to generate a fault-tolerant BPEL process. We also develop a GUI tool to assist designers to specify ECA rules. Experiments show our approach is feasible.

Multi-task assignment for crowdsensing in mobile social networks

Mobile crowdsensing is a new paradigm in which a crowd of mobile users exploit their carried smart devices to conduct complex computation and sensing tasks in mobile social networks (MSNs). In this paper, we focus on the task assignment problem in mobile crowdsensing. Unlike traditional task scheduling problems, the task assignment in mobile crowdsensing must follow the mobility model of users in MSNs. To solve this problem, we propose an oFfline Task Assignment (FTA) algorithm and an oNline Task Assignment (NTA) algorithm. Both FTA and NTA adopt a greedy task assignment strategy. Moreover, we prove that the FTA algorithm is an optimal offline task assignment algorithm, and give a competitive ratio of the NTA algorithm. In addition, we demonstrate the significant performance of our algorithms through extensive simulations, based on four real MSN traces and a synthetic MSN trace.

TOUR: Time-sensitive Opportunistic Utility-based Routing in delay tolerant networks

In this paper, we propose a time-sensitive utility model for delay tolerant networks (DTNs), in which each message has an attached time-sensitive benefit that decays over time. The utility of a message is the benefit minus the transmission cost incurred by delivering the message. This model is analogous to the postal service in the real world, which inherently provides a good balance between delay and cost. Under this model, we propose a Time-sensitive Opportunistic Utility-based Routing (TOUR) algorithm. TOUR is a single-copy opportunistic routing algorithm, in which a time-sensitive forwarding set is maintained for each node by considering the probabilistic contacts in DTNs. By forwarding messages via nodes in these sets, TOUR can achieve the optimal expected utilities. We show the outstanding performance of TOUR through extensive simulations with several real DTN traces. To the best of our knowledge, TOUR is the first utility-based routing algorithm in DTNs.

Truthful Auction Mechanisms with Performance Guarantee in Secondary Spectrum Markets

We study a spectrum auction problem where each request from new spectrum users has spatial, temporal, and spectral features. Our goal is to design truthful auction mechanisms that maximize either the overall social efficiency of new users (a.k.a buyers) or the revenue of the spectrum owner (a.k.a seller). Given that the optimal conflict-free spectrum allocation problem is NP-hard, this paper proposes a series of near-optimal auction mechanisms based on the following approximation techniques: linear programming (LP) relaxation, randomized rounding, derandomized rounding, monotone derandomization, and Lavi-Swamy method. Comparing with the prior art, we make two significant advances: First, our auction mechanisms are not only truthful but also provide theoretically-provable performance guarantee, an important feature that existing work under the same auction model does not have. Second, our auction mechanisms support both spatial and temporal spectral reuse, which makes the problem more challenging than existing work that deals with only spatial or temporal reuse. We perform extensive simulations to study the performance of the proposed mechanisms, and the simulation results corroborate our theoretical analysis.

Home-Based Zero-Knowledge Multi-Copy Routing in Mobile Social Networks

A mobile social network (MSN) is a special kind of delay tolerant network (DTN) composed of mobile nodes that move around and share information with each other through their carried short-distance wireless communication devices. A main characteristic of MSNs is that mobile nodes in the networks generally visit some locations (namely, community homes) frequently, while visiting other locations less frequently. In this paper, we propose a novel zero-knowledge multi-copy routing algorithm, homing spread (HS), for homogeneous MSNs, in which all mobile nodes share all community homes. HS is a distributed and localized algorithm. It mainly lets community homes spread messages with a higher priority. Theoretical analysis shows that HS can spread a given number of message copies in an optimal way when the inter-meeting time between any two nodes and between a node and a community home follows independent and identical exponential distributions, respectively. We also extend HS to the heterogeneous MSNs, where mobile nodes have different community homes. In addition, we calculate the expected delivery delay of HS, and conduct extensive simulations. Results show that community homes are important factors in message spreading. By using homes to spread messages faster, HS achieves a better performance than existing zero-knowledge MSN routing algorithms, including Epidemic (with a given number of copies), and Spray&Wait.

Hierarchical cooperative caching in mobile opportunistic social networks

A mobile opportunistic social network (MOSN) is a new type of delay tolerant network (DTN), in which the mobile users contact each other opportunistically. While cooperative caching in the Internet has been studied extensively, cooperative caching in MOSNs is a considerably different and challenging problem due to the probabilistic nature of contact among the mobile users in MOSNs. In order to reduce the total access delay, we let the mobile users cooperatively cache these data items in their limited buffer space. We balance between selfishness (caching the data items according to its own preference) and unselfishness (helping other nodes to cache). The friends with higher contact frequency may share similar interests, hence, caching the data items for friend users can lead to some benefit. In this paper, we present a hierarchical cooperative caching scheme, which divides the buffer space into three components: self, friends, and strangers. In the self component, mobile users cache the data items according to their preference. In the friends component, mobile users help their friends to cache some data items. In the strangers component, mobile users randomly cache the remaining data items. We formally analyze the access delay of the proposed scheme. The effectiveness of our approach is verified through extensive real world trace-driven simulations.

Privacy Preserving C4.5 Algorithm Over Horizontally Partitioned Data

For the problem of decision tree classification with privacy concerns, we propose several efficient secure multi-party computation protocols to construct a privacy preserving ID3 algorithm over horizontally partitioned data among multiple parties. Our algorithm presents the first solution to privacy preserving decision tree classification among more than two parties. We also make a performance comparison with the existing solution, which is only applicable to the twoparty case. The result shows that our solution has a significantly better performance.