Ding-Chau Wang

A Survey of Mobile Cloud Computing Applications: Perspectives and Challenges

As mobile computing has been developed for decades, a new model for mobile computing, namely, mobile cloud computing, emerges resulting from the marriage of powerful yet affordable mobile devices and cloud computing. In this paper we survey existing mobile cloud computing applications, as well as speculate future generation mobile cloud computing applications. We provide insights for the enabling technologies and challenges that lie ahead for us to move forward from mobile computing to mobile cloud computing for building the next generation mobile cloud applications. For each of the challenges, we provide a survey of existing solutions, identify research gaps, and suggest future research areas.

Analysis of Replicated Data with Repair Dependency

Pessimistic control algorithms for replicated data permit only one partition to perform update operations at any time so as to ensure mutual exclusion of the replicated data object. Existing availability modelling and analyses of pessimistic control algorithms for replicated data management are constrained to either site-failure-only or link-failure-only models, but not both, because of the large state space which needs to be considered. Moreover, the assumption of having an independent repairman for each link and each site has been made to reduce the complexity of analysis. In this paper, we remove these restrictions with the help of stochastic Petri nets. In addition to including both site and link failures/repairs events in our analysis, we investigate the effect of repair dependency which occurs when many sites and links may have to share the same repairman due to repair constraints. Four repairman models are examined in the paper: (a) independent repairman with one repairman assigned to each link and each node; (b) dependent repairman with FIFO servicing discipline; (c) dependent repairman with linear-order servicing discipline; and (d) dependent repairman with best-first servicing discipline. Using dynamic voting as a case study, we compare and contrast the resulting availabilities due to the use of these four different repairman models and give a physical interpretation of the differences. We show that ignoring concurrent site and link failures/repairs events or repair dependency can very unrealistically overestimate the availability of replicated data.

Performance optimization of region-based group key management in mobile ad hoc networks

We propose and analyse a scalable and efficient region-based group key management protocol for secure group communications in mobile ad hoc networks. For scalability and dynamic reconfigurability, we take a region-based approach by which group members are broken into region-based subgroups. Leaders in subgroups securely communicate with each other to agree on a group key in response to membership change and member mobility-induced events. We propose a novel approach to identify the optimal setting of the region-based key management protocol to maximize the performance of the system. We show that secrecy requirements for secure group communication are satisfied, and that there exists an optimal region size that minimizes the network traffic as a result of efficiently trading inter-regional vs. intra-regional group key management overheads. We compare the proposed region-based key management protocol with nonregion-based key management to demonstrate the effectiveness. Analytical results are validated by extensive simulation.

Reliability of wireless sensors with code attestation for intrusion detection

Wireless sensor nodes are widely used in many areas, including military operation surveillance, natural phenomenon monitoring, and medical diagnosis data collection. These applications need to store and transmit sensitive or secret data, which requires intrusion detection mechanisms be deployed to ensure sensor node health, as well as to maintain sensor quality of service and survivability. Because wireless sensors have inherent resource constraints, it is crucial to reduce energy consumption due to intrusion detection activities. In this paper by means of a probability model, we analyze the best frequency at which intrusion detection based on code attestation on the sensor node should be performed so that the sensor reliability is maximized by exploiting the trade-off between the energy consumption and intrusion detection effectiveness. When given a set of parameter values characterizing the operational and networking conditions, the system verifier can dynamically set the intrusion detection rate identified by the mathematical model to maximize the sensor reliability and the expected sensor lifetime.

Regional Registration-Based Mobile Multicast Service Management in Mobile IP Networks

We propose and analyze a regional registration based mobile multicast service management scheme which we call URRMoM for efficiently supporting mobile multicast in Mobile IP networks. URRMoM extends the design concept of Remote Subscription (RS) by using mobile multicast agents (MMAs), each covering a number of MHs in its service area through tunneling multicast packets received from the multicast source to them. URRMoM adopts a user-central design allowing each mobile host to determine its optimal MMA service area dynamically depending on its service and mobility characteristics. We develop an analytical model to describe the behavior of a MH operating under URRMoM and derive the optimal service area of the MMA based on the MH’s service and mobility characteristics to minimize the total network traffic generated due to multicast packet delivery and multicast tree maintenance. We present analytical results validated by simulation to demonstrate the benefit of our proposed regional registration based mobile multicast service management scheme over existing schemes including RS and RBMoM.

Trust-based cooperative spectrum sensing against SSDF attacks in distributed cognitive radio networks

We propose and analyze a trust-based data fusion scheme against spectrum sensing data falsification attacks in a distributed cognitive radio network. Our trust-based data fusion scheme is based on mechanism design theory to motivate users to report authentic sensing data so as to improve the success rate. Further, we decouple erroneous sensing reports due to low sensing capabilities from false reports due to attacks, thus avoiding unnecessary punishments to benign users. We conduct a theoretical analysis validated with extensive simulation and identify optimal parameter settings under which our trust-based data fusion scheme outperforms existing non-trust based data fusion schemes.

Performance characteristics of region-based group key management in mobile ad hoc networks

We propose and analyze a scalable and efficient region-based group key management protocol for secure group communications in mobile ad hoc networks. For scalability and dynamic reconfigurability, we take a region-based approach by which group members are broken into region-based subgroups and leaders in subgroups securely communicate with each other to agree on a group key in response to membership change and member mobility events. We show that the secrecy requirement for group communication is satisfied. Further, there exists an optimal regional size that minimizes the total network communication cost as a result of efficiently trading inter-regional vs. intra-regional group key management overheads. We give an analytical expression of the cost involved which allows the optimal regional size to be identified, when given a set of parameter values characterizing a group communicating system in mobile ad hoc networks

Analyzing reconfigurable algorithms for managing replicated data with strict consistency requirements: a case study

We address reconfigurable algorithms for managing replicated data with strict consistency requirements, that is, whenever the user performs an update operation, the update is applied to all reachable copies as part of the update protocol. A key issue of designing such algorithms is to determine how often one should detect and react to failure conditions so that reorganization operations can be performed at the appropriate time to improve the availability of replicated data. We use dynamic voting as a case study to illustrate how often such failure detection and reconfiguration activities should be performed so as to maximize the data availability. We show that there exists an optimal period at which the failure detection and reconfiguration activities should be performed to optimize the system availability. Stochastic Petri nets (SPNs) are used as a tool to facilitate our analysis.

Scalable and efficient dual-region based mobility management for ad hoc networks

In this paper, we propose and analyze the design notion of dual-region mobility management (DrMoM) for achieving scalable, efficient location management of mobile nodes in ad hoc networks. The basic idea is to employ local regions to complement existing home region based location service schemes that assign a home region through hashing to a mobile node and have mobile nodes in both the home and local regions serve as location servers for that node. The most salient feature of DrMoM is that the optimal home region size and local region size can be dynamically determined per mobile user based on mobility and service characteristics of individual mobile nodes to minimize the overall network cost incurred by location management and data packet delivery. Moreover, DrMoM is completely distributed. Each node determines its optimal home region size and local region size autonomously. A performance analysis is performed to demonstrate the benefit of DrMoM over existing region-based location management schemes.

Analyzing User-Perceived Dependability and Performance Characteristics of Voting Algorithms for Managing Replicated Data

User-perceived dependability and performance metrics are very different from conventional ones in that the dependability and performance properties must be assessed from the perspective of users accessing the system. In this paper, we develop techniques based on stochastic Petri nets (SPN) to analyze user-perceived dependability and performance properties of quorum-based algorithms for managing replicated data. A feature of the techniques developed in the paper is that no assumption is made regarding the interconnection topology, the number of replicas, or the quorum definition used by the replicated system, thus making it applicable to a wide class of quorum-based algorithms. We illustrate this technique by comparing conventional and user-perceived metrics in majority voting algorithms. Our analysis shows that when the user-perceiveness is taken into consideration, the effect of increasing the network connectivity and number of replicas on the availability and dependability properties perceived by users is very different from that under conventional metrics. Thus, unlike conventional metrics, user-perceived metrics allow a tradeoff to be exploited between the hardware invested, i.e., higher network connectivity and number of replicas, and the performance and dependability properties perceived by users.