Sheng-Tzong Cheng

Topological optimization of a reliable communication network

This paper considers backbone network design under the constraints: minimal total link cost, and 1-FT (fault-tolerant to 1 link-failure). As networks become huge, the backbone layout design is essential to network performance and reliability. A 1-FT backbone can survive any 1-link failure. On the other hand, the total cost of the links in backbone layout is a practical concern. Therefore, the problem is to find a network topology for a set of nodes whose total link cost is minimized, subject to the condition that the backbone network can accommodate 1 link failure. The problem is NP-hard, and methods based on heuristic search are desired to obtain optimal or sub-optimal solutions. This paper proposes an efficient method based on genetic algorithms to solve the problem. The representation of a backbone layout is based on a list of ordered links. The genetic operators attempt to generate a more cost-effective or reliable layout. Simulation shows that the proposed algorithm can efficiently find a sub-optimal solution for most cases.

A new framework for mobile Web services

The goal of the paper is to propose a way to make Web services more convenient and efficient to use. We develop an architecture that integrates mobile agents with Web services to achieve the goal. We first survey the key technologies, which are adopted in the paper. Next, we introduce our mobile Web service framework and describe how we take advantage of the location information in the Web service. Finally, we give an example to illustrate a typical scenario in which a mobile user receives Web services from our proposed platform.

Quantum communication for wireless wide-area networks

In this paper, a quantum routing mechanism is proposed to teleport a quantum state from one quantum device to another wirelessly even though these two devices do not share EPR pairs mutually. This results in the proposed quantum routing mechanism that can be used to construct the quantum wireless networks. In terms of time complexity, the proposed mechanism transports a quantum bit in time almost the same as the quantum teleportation does regardless of the number of hops between the source and destination. From this point of view, the quantum routing mechanism is close to optimal in data transmission time. In addition, in order to realize the wireless communication in the quantum domain, a hierarchical network architecture and its corresponding communication protocol are developed. Based on these network components, a scalable quantum wireless communication can be achieved.

Quantum switching and quantum merge sorting

This paper proposes a quantum switching architecture that can dynamically permute each input quantum data to its destination port to avoid using the fully connected networks. In addition, in order to reduce the execution time of the quantum switching, an efficient quantum merge sorting (QMS) algorithm that provides a parallel quantum computation is also developed. The quantum switching utilizes the QMS algorithm as a subroutine so that the total running time can be reduced to polylogarithmic time. Furthermore, to evaluate the feasibility of the quantum switching, we also define three different kinds of performance factors that can be used to estimate the complexity in implementation and the time delay in execution for quantum instruments. From the evaluation results, it can be seen that the proposed quantum switching is feasible in practice.

Performance evaluation of an admission control algorithm: dynamic threshold with negotiation

An admission control algorithm for a multimedia server is responsible for determining if a new request can be accepted without violating the QoS requirements of the existing requests in the system. Most admission control algorithms treat every request uniformly and hence optimize the system performance by maximizing the number of admitted and served requests. In practice, requests might have different levels of importance to the system. Requests offering high contribution or reward to the system performance deserve priority treatment. Failure of accepting a high-priority request would incur high penalty to the system.A novel threshold-based admission control algorithm with negotiation for two priority classes of requests is proposed in our previous study. The server capacity is divided into three partitions based on the threshold values: one for each class of requests and one common pool shared by two classes of requests. Reward and penalty are adopted in the proposed system model. High-priority requests are associated with higher values of reward as well as penalty than low-priority ones. In this paper, given the characteristics of the system workload, the proposed analytical models aim to finds the best partitions, optimizing the system performance based on the objective function of the total reward minus the total penalty. The negotiation mechanism reduces the QoS requirements of several low-priority clients, by cutting out a small fraction of the assigned server capacity, to accept a new high-priority client and to achieve a higher net earning value. Stochastic Petri-Net model is used to find the optimal threshold values and two analytical methods are developed to find sub-optimal settings. The experiment results show that the sub-optimal solutions found by the proposed analytical methods are very close to optimal ones. The methods enable the algorithm to dynamically adjust the threshold values, based on the characteristics of the system workload, to achieve higher system performance.

Dynamic quota-based admission control with sub-rating in multimedia servers

Abstract. An admission control algorithm for a multimedia server is responsible for determining if a new request can be accepted without violating the Quality of Service (QoS) requirements of the existing requests in the system. A novel quota-based admission control algorithm with sub-rating for two priority classes of requests is proposed in this study. The server capacity is divided into three partitions based on the quota values: one for each class of requests and one common pool shared by two classes of requests. Reward and penalty are adopted in the proposed system model. High-priority requests are associated with higher values of reward as well as penalty than low-priority ones. Given the characteristics of the system workload, the proposed algorithm finds the best partitions, optimizing the system performance based on the objective function of the total reward minus the total penalty. The sub-rating mechanism will reduce the QoS requirements of several low- priority clients, by cutting out a small fraction of the assigned server capacity, to accept a new high- priority client and to achieve a higher net earning value. A stochastic Petri-Net model is used to find the optimal quota values and two approximation approaches are developed to find sub-optimal settings. The experiment results show that the proposed algorithm performs better than one without sub-rating mechanism, and that the sub-optimal solutions found by the proposed approximation approaches are very close to optimal ones. The approximation approaches enable the algorithm to dynamically adjust the quota values, based on the characteristics of the system workload, to achieve higher system performance.

On failure recoverability of client-server applications in mobile wireless environments

Analytical results for the Cdf of the failure recovery time for client-server applications in mobile wireless environments characterized by logging, and mobility handoff strategies for facilitating failure recovery are reported in the paper. The results can be applied to determine if a mobile application can satisfy its recoverability requirement upon a mobile host failure when operating under a set of parameter values characterizing the mobile application, the underlying client-server environment, and the logging & mobility handoff strategies adopted by the mobile application. Model parameters which affect the shape of the failure recovery time Cdf for two mobility handoff strategies, namely, Eager and Lazy, are identified, and their effects are analyzed, with numerical data and result interpretations given. A tradeoff analysis between the cost invested by these two mobility handoff strategies for maintaining the logging and checkpoint information before failure versus the return of investment in terms of improved failure recoverability is given, and the best checkpoint interval period that would yield the best return of investment for the eager mobility handoff strategy over the lazy strategy is identified.

Allocation and scheduling of real-time periodic tasks with relative timing constraints

Allocation problem has always been one of the fundamental issues of building the applications in real-time computing systems. For real-time applications, the allocation problem should directly address the issues of task and communication scheduling. In this context, the allocation of tasks has to fully utilize the available processors and the scheduling of tasks has to meet the specified timing constraints. Clearly, the execution of tasks under the allocation and schedule has to satisfy the precedence, resources, and other synchronization constraints among them. Recently, the timing requirements of the real-time systems emerge that the relative timing constraints are imposed on the consecutive executions of each task and the inter-task temporal relationships are specified across task periods. In this paper we consider the allocation and scheduling problem of the periodic tasks with such timing requirements. Given a set of periodic tasks, we consider the least common multiple (LCM) of the task periods. Each task is extended to several instances within the LCM. The scheduling window for each task instance is derived to satisfy the timing constraints. We develop a simulated annealing algorithm as the overall control algorithm. An example problem of the sanitized version of the Boeing 777 Aircraft Information Management System is solved by the algorithm. Experimental results show that the algorithm solves the problem in a reasonable time complexity.

An adaptive learning scheme for load balancing with zone partition in multi-sink wireless sensor network

Highlights? We propose an adaptive learning scheme for load balancing scheme in multi-sink WSN. ? The mobile anchor adaptively partitions the network into several zones. ? The agent learns to balance the load in the way of reallocate the collection zones. ?The agent applies the residual energy of hotspots around sink nodes. ?The proposed QAZP scheme prolongs the lifetime of the wireless sensor network. In many researches on load balancing in multi-sink WSN, sensors usually choose the nearest sink as destination for sending data. However, in WSN, events often occur in specific area. If all sensors in this area all follow the nearest-sink strategy, sensors around nearest sink called hotspot will exhaust energy early. It means that this sink is isolated from network early and numbers of routing paths are broken. In this paper, we propose an adaptive learning scheme for load balancing scheme in multi-sink WSN. The agent in a centralized mobile anchor with directional antenna is introduced to adaptively partition the network into several zones according to the residual energy of hotspots around sink nodes. In addition, machine learning is applied to the mobile anchor to make it adaptable to any traffic pattern. Through interactions with the environment, the agent can discovery a near-optimal control policy for movement of mobile anchor. The policy can achieve minimization of residual energys variance among sinks, which prevent the early isolation of sink and prolong the network lifetime.

OSGi-based smart home architecture for heterogeneous network

With the development of home network and service applications, different protocols and transmission modes are proposed. More digital devices and home appliance compliance to the protocols in the development. The proposed protocols are usually unable to communicate with each other; we design and implement a service-oriented smart-home architecture to integrate popular protocols such as UPnP, Jini, DPWS on OSGi framework and collaborating Tmote, Zigbee and Bluetooth to converge various service oriented applications. Furthermore, with the well-developed Tmote, Zigbee and Bluetooth technology, majority of devices developed with these technologies supported, we propose the three new base drivers to integrate different devices communication on our platform. Additionally, we propose a Service Resolving Bundle to complement the drawbacks of OSGi mechanisms. This architecture with service-oriented mechanisms accommodates applications implemented across different domains and allows system components to interact with one another.