VISP: on Implementing a Video Streaming Protocol for the Internet

A recently proposed mechanism introduced a new approach to support interactive video streaming applications over the Internet. It acts on the video QoS in order to avoid possible problems caused by the network jitter. Simulations results proved the effectiveness of this mechanism. An exhaustive discussion on the implementation of this mechanism is the contribution of this paper. A client-server protocol, named VISP (VIdeo Streaming Protocol), is designed to support interactive video streaming applications over the Internet. VISP is not a video compression scheme and it is not a transport protocol, but an application protocol that controls the video transmission to provide interactivity. Several features have been added in order to complete the protocol and tests confirm that VISP is effective in supporting interactive video streaming applications over the Internet

Scalable and Efficient Parallel and Distributed Simulation of Complex, Dynamic and Mobile Systems.

In this work we illustrate the design and implementation guidelines of a recently developed middleware defined to support the parallel and distributed simulation of large scale, complex and dynamically interacting system models. The distributed simulation of complex system models, may suffer the communication and synchronization required to maintain the causality constraints between distributed model components. We designed and implemented the ART\uccS middleware as a new framework by incorporating a set of features that allow adaptive optimization by exploiting many complex and dynamic model and distributed simulation characteristics. As an example, a dynamic migration mechanism for the run-time adaptive allocation of model entities has been designed and exploited for dynamic load and communication balancing. Optimizations have been introduced to obtain the maximum advantage from heterogeneous and asymmetric communication systems, from shared memory to LAN and Internet communication. Other optimizations have been introduced by the exploitation of concurrent replications of parallel and distributed simulations, in order to increase the resources utilization and to maximize the speedup of simulation processes. Solutions have been designed, implemented and tuned to obtain a significant reduction in the communication and synchronization overheads between the physical execution units, and an increased model scalability and simulation speedup, even in worst-case modeling assumptions and simulation scenarios

An Adaptive Load Balancing Middleware for Distributed Simulation

The simulation is useful to support the design and performance evaluation of complex systems, possibly composed by a massive number of interacting entities. For this reason, the simulation of such systems may need aggregate computation and memory resources obtained by clusters of parallel and distributed execution units. Shared computer clusters composed of available Commercial-Off-the-Shelf hardware are preferable to dedicated systems, mainly for cost reasons. The performance of distributed simulations is influenced by the heterogeneity of execution units and by their respective CPU load in background. Adaptive load balancing mechanisms could improve the resources utilization and the simulation process execution, by dynamically tuning the simulation load with an eye to the synchronization and communication overheads reduction. In this work it will be presented the GAIA+ framework: a new load balancing mechanism for distributed simulation. The framework has been evaluated by performing testbed simulations of a wireless ad hoc network model. Results confirm the effectiveness of the proposed solutions

Performance analysis of a parallel and distributed simulation framework for large scale wireless systems

The simulation of ad hoc and sensor networks often requires a large amount of computation, memory and time to obtain significant results. The parallel and distributed simulation approach can be a valuable solution to reduce the computation time, and to support model components' modularity and reuse. In this work we perform a testbed evaluation of a new middleware for the simulation of large scale wireless systems. The proposed middleware has been designed to adapt and to scale over a heterogeneous distributed execution infrastructure. To realize a testbed evaluation of the considered framework we implemented and investigated a set of wireless systems' models. Specifically, we identified two classes of widely investigated wireless models: mobile ad hoc, and static sensor networks. In this work we present the performances of the simulation framework, with respect to the heterogeneous set of execution architectures, and the modeled systems' characteristics. Results demonstrate that the framework leads to increased model scalability and speed-up, by transparently adapting and managing at runtime the communication and synchronization overheads, and the load balancing

Concurrent Replication of Parallel and Distributed Simulations

Parallel and distributed simulations enable the analysis of complex systems by concurrently exploiting the aggregate computation power and memory of clusters of execution units. In this paper we investigate a new direction for increasing both the speedup of a simulation process and the utilization of computation and communication resources. Many simulation-based investigations require to collect independent observations for a correct and significant statistical analysis of results. The execution of many independent parallel or distributed simulation runs may suffer the speedup reduction due to rollbacks under the optimistic approach, and due to idle CPU times originated by synchronization and communication bottlenecks under the conservative approach. We present a parallel and distributed simulation framework supporting Concurrent Replication of Parallel and Distributed Simulations (CR-PADS), as an alternative to the execution of a linear sequence of multiple parallel or distributed simulation runs. Results obtained from tests executed under variable scenarios show that speedup and resource utilization gains could be obtained by adopting the proposed replication approach in addition to the pure parallel and distributed simulation

ARTIS: A parallel and distributed simulation middleware for performance evaluation

This paper illustrates the motivation, the preliminary design and implementation issues, of a new distributed simulation middleware named Advanced RTI System (ARTÌS). The aim of the ARTÌS middleware is to support parallel and distributed simulations of complex systems characterized by heterogeneous and distributed model components. The ARTÌS design is oriented to support the model components heterogeneity, distribution and reuse, and to increase the simulation performances, scalability and speedup, in parallel and distributed simulation scenarios. Another design issue of the ARTÌS framework is the dynamic adaptation of the interprocess communication layer to the heterogeneous communication support of different simulation scenarios. In this paper we illustrate the guidelines and architecture that we considered in the design and implementation of the ARTÌS middleware, and we sketch some case studies that demonstrated the ARTÌS utility and motivation, e.g., a distributed simulation of massively populated wireless ad hoc and sensor networks

MoVES: a Framework for Parallel and Distributed Simulation of Wireless Vehicular Ad Hoc Networks

In this paper, we illustrate a Mobile Wireless Vehicular Environment Simulation (MoVES) framework for the parallel and distributed simulation of vehicular wireless ad hoc networks (VANETs). The proposed framework supports extensible, module-based and layered modeling, and scalable, accurate and efficient simulation of vehicular scenarios integrated with wireless communication and mobile services/applications. The vehicular layer includes models for vehicles, synthetic and trace-driven mobility, driver behavior, GPS-based street maps, intersection policies and traffic lights. The wireless communication layer currently includes models for physical propagation, and a network protocol stack including IEEE 802.11 Medium Access Control, up to the Application layer. MoVES provides a platform for microscopic modeling and simulation-based analysis of wireless vehicular scenarios and communication-based services and applications, like Intelligent Transportation Systems, communication-based monitoring/control and info-mobility services. The framework includes design solutions for scalable, accurate and efficient parallel and distributed simulation of complex, vehicular communication scenarios executed over cost-effective, commercial-off-the-shelf (COTS) simulation architectures. Dynamic model partition and adaptation-based load balancing solutions have been designed by exploiting common assumptions and model characteristics, in a user-transparent way. Test-bed performance evaluation for realistic scenarios has shown the effectiveness of MoVES in terms of simulation efficiency, scalability, adaptation and simulation accuracy

Identification of candidate MLO powdery mildew susceptibility genes in cultivated Solanaceae and functional characterization of tobacco NtMLO1

Specific homologs of the plant Mildew Locus O (MLO) gene family act as susceptibility factors towards the powdery mildew (PM) fungal disease, causing significant economic losses in agricultural settings. Thus, in order to obtain PM resistant phenotypes, a general breeding strategy has been proposed, based on the selective inactivation of MLO susceptibility genes across cultivated species. In this study, PCR-based methodologies were used in order to isolate MLO genes from cultivated solanaceous crops that are hosts for PM fungi, namely eggplant, potato and tobacco, which were named SmMLO1, StMLO1 and NtMLO1, respectively. Based on phylogenetic analysis and sequence alignment, these genes were predicted to be orthologs of tomato SlMLO1 and pepper CaMLO2, previously shown to be required for PM pathogenesis. Full-length sequence of the tobacco homolog NtMLO1 was used for a heterologous transgenic complementation assay, resulting in its characterization as a PM susceptibility gene. The same assay showed that a single nucleotide change in a mutated NtMLO1 allele leads to complete gene loss-of-function. Results here presented, also including a complete overview of the tobacco and potato MLO gene families, are valuable to study MLO gene evolution in Solanaceae and for molecular breeding approaches aimed at introducing PM resistance using strategies of reverse genetics