SIMULATION: Transactions of The Society for Modeling and Simulation International

Schultz, Joel Jeffrey; Znati, Taieb

doi: 10.1177/0037549703037146pmid: N/A

As the Internet becomes a more popular distribution channel for multimedia, one inevitably encounters the problem of the amount of bandwidth required for quality multimedia presentations. Bandwidth may be controlled through various techniques such as compression, caching, or layered encoding of data. These techniques, however, may be unsuitable for applications with stringent quality of service requirements, as it may lead to severe degradations of the quality of the content being distributed. This article proposes a new version of a media content delivery algorithm, based on the “chaining” strategy, that supports “VCR operations.” The proposed algorithm explicitly balances the client-side requirements to support the VCR functionalities while preserving the advantages of using the client playback device as a proxy video server, as specified in the original chaining algorithm. The article also investigates the effect of supporting VCR operations on the performance of the proposed scheme and the impact these operations have on chaining.

Karatza, Helen D.; Hilzer, Ralph C.

doi: 10.1177/0037549703037148pmid: N/A

The performance of parallel programs such as those involving fork-join instructions is significantly affected by the method used to schedule program tasks. This article studies parallel job scheduling in homogeneous distributed systems. A simulation model is used to address performance issues associated with scheduling. Various policies are employed to schedule parallel jobs over a variety of workloads. Fairness is required among competing jobs. The authors examine cases in which the distribution of the number of parallel tasks per job, as well as the distribution of task service demand, varies with time. They also examine the impact of overhead necessary to collect global system information about processor queues on performance. Simulated results indicate that although all scheduling methods have merit, one significantly improves the overall performance and guarantees fairness in terms of individual job execution.

Chen, Dan; Turner, Stephen John; Gan, Boon Ping; Cai, Wentong; Wei, Junhu; Julka, Nirupam

doi: 10.1177/0037549703037147pmid: N/A

Simulation cloning is designed to satisfy the requirement of examining alternative scenarios concurrently. This article discusses the issues involved in cloning distributed simulations based on the High Level Architecture (HLA) and proposes tentative solutions. Alternative solutions are compared from both the qualitative and quantitative point of view. In terms of federation organization, candidate solutions can be classified into the single-federation and the multiple-federation categories. To guarantee the correctness and optimize the performance of the whole cloning-enabled distributed simulation, the single-federation solution requires an additional mechanism to isolate the interactions among alternative executions. Data distribution management (DDM) is one of the candidate approaches. To measure the trade-off between complexity and efficiency, the authors introduce a series of experiments to benchmark various solutions at the runtime infrastructure (RTI) level. The benchmark results indicate that the single-federation solution provides encouraging performance when using DDM.

Chen, Yinong; He, Zhongshi

doi: 10.1177/0037549703037150pmid: N/A

The aim of the research is to investigate techniques that support the development of highly dependable applications in a distributed system environment. Techniques developed include redundant task allocation, load balancing, fault-tolerant computing, and communication. The application the authors have implemented in the system is a firewall application. The firewall runs in redundant mode. Each incoming or outgoing packet is checked by two or more copies of the firewall application. Only when the majority of the firewall copies decide to accept the packet can the packet go through the firewall. Disagreed decision from the different firewall copies signify a possible hardware fault or a software error in the underlying system. This article reports a recent implementation of a simulation system in which computing nodes, redundant copies of tasks, and packet queues are implemented as independent threads, as well as experiment results obtained based on queuing models.

Mills-Tettey, G. Ayorkor; Wilson, Linda F.

doi: 10.1177/0037549703037149pmid: N/A

The Agent-Based Environment for Linking Simulations (ABELS) framework is designed to allow independent and physically distributed simulations and other data resources to form a “data cloud” for the exchange of information. In particular, it uses a distributed brokering system to facilitate dynamic linkings between independently designed, autonomous participants, without requiring the use of stringent standards to which participants must conform. This article discusses the various security threats that can arise in the ABELS architecture and presents the current design and implementation of a security framework for the system.

Silva, Aloizio P.; Mateus, Geraldo R.

doi: 10.1177/0037549703037151pmid: N/A

The convergence of multiple technologies has given rise to new types of information utilities called mobile location-based services. Specifically, the authors examine a context in which people need to move physically from one location to another via taxis. In this scenario, the user is in control of the location information associated with the mobile device. However, problems arise when a fleet management application uses that dynamic information to provide the best taxi assignment. This particular vehicle-routing problem aims to allocate a taxi fleet to a number of mobile units to minimize the running distance and time. This article presents a new approach to the taxi assignment problem in a mobile environment based on optimization and simulation. Its specific interest is to predict the impact of the interaction between the assignment algorithm and fleet management in the mobile environment on the desired quality of service for mobile users.