F. De Turck

Dimensioning of survivable WDM networks

In this paper routing, planning of working capacity, rerouting, and planning of spare capacity in wavelength division multiplexing (WDM) networks are investigated. Integer linear programming (ILP) and simulated annealing (SA) are used as solution techniques. A complex cost model is presented. The spare capacity assignment is optimized with respect to three restoration strategies. The benefit of wavelength conversion, the choice of the fiber line system, and the influence of cost parameter values are discussed, with respect to the different restoration strategies and solution techniques. Wavelength conversion is found to be of limited importance, whereas tunability at the end points of the connections has substantial benefits.

A hybrid thin-client protocol for multimedia streaming and interactive gaming applications

Despite the growing popularity and advantages of thin-client systems, they still have some important shortcomings. Current thin-client systems are ideally suited to be used with classic office-applications but as soon as multimedia and 3D gaming applications are used they require a large amount of bandwidth and processing power. Furthermore, most of these applications heavily rely on the Graphical Processing Unit (GPU). Due to the architectural design of thin-client systems, they cannot profit from the GPU resulting in slow performance and bad image quality. In this paper, we propose a thin-client system which addresses these problems: we introduce a realtime desktopstreamer using a videocodec to stream the graphical output of applications after GPU-processing to a thin-client device, capable of decoding a videostream. We compare this approach to a number of popular classic thin-client systems in terms of bandwidth, delay and image quality. The outcome is an architecture for a hybrid protocol, which can dynamically switch between a classic thin-client protocol and realtime desktopstreaming.

Adaptive Task Checkpointing and Replication: Toward Efficient Fault-Tolerant Grids

A grid is a distributed computational and storage environment often composed of heterogeneous autonomously managed subsystems. As a result, varying resource availability becomes commonplace, often resulting in loss and delay of executing jobs. To ensure good grid performance, fault tolerance should be taken into account. Commonly utilized techniques for providing fault tolerance in distributed systems are periodic job checkpointing and replication. While very robust, both techniques can delay job execution if inappropriate checkpointing intervals and replica numbers are chosen. This paper introduces several heuristics that dynamically adapt the above mentioned parameters based on information on grid status to provide high job throughput in the presence of failure while reducing the system overhead. Furthermore, a novel fault-tolerant algorithm combining checkpointing and replication is presented. The proposed methods are evaluated in a newly developed grid simulation environment dynamic scheduling in distributed environments (DSiDE), which allows for easy modeling of dynamic system and job behavior. Simulations are run employing workload and system parameters derived from logs that were collected from several large-scale parallel production systems. Experiments have shown that adaptive approaches can considerably improve system performance, while the preference for one of the solutions depends on particular system characteristics, such as load, job submission patterns, and failure frequency.

Remote Display Solutions for Mobile Cloud Computing

Proposed optimization techniques address the major challenges that varying wireless channel conditions, short battery lifetime, and interaction latency pose for the remote display of cloud applications on mobile devices.

A view on enabling-consumer oriented grids through optical burst switching

As grid computing continues to gain popularity in the research community, it also attracts more attention from the enterprise and consumer levels. Applications in these domains generate large amounts of jobs, with individual jobs having only modest resource requirements. In this article, a novel architecture to realize a highly scalable and flexible platform for consumer-oriented grids is proposed. The architecture is based on an optical burst switched network, complemented with an advanced control and signaling plane. The architecture, functionality, and interfaces of all the relevant entities are presented and issues, current initiatives, and future directions for the control and management of these grid networks are discussed.

Blind Kriging: Implementation and performance analysis

When analysing data from computationally expensive simulation codes or process measurements, surrogate modelling methods are firmly established as facilitators for design space exploration, sensitivity analysis, visualisation and optimisation. Kriging is a popular surrogate modelling technique for data based on deterministic computer experiments. There exist several types of Kriging, mostly differing in the type of regression function used. Recently a promising new variable selection technique was proposed to identify a regression function in the Kriging framework. In this paper this type of Kriging, i.e., blind Kriging, has been efficiently implemented in Matlab(R) and has been extended. The implementation is validated and tested on several examples to illustrate the strength and weaknesses of this new, promising modelling technique. It is shown that the performance of blind Kriging is as good as, or better than ordinary Kriging. Though, blind Kriging comes at double the computational cost with respect to ordinary Kriging.

Design and implementation of a hybrid remote display protocol to optimize multimedia experience on thin client devices

In a thin client computing architecture, application processing is delegated to a remote server rather than running the application locally. User input is forwarded to the server, and the rendered images are relayed through a dedicated remote display protocol to the users device. Existing remote display protocols have been successfully optimized for applications with only minor and low-frequent screen updates, such as a spreadsheet or a text editor. However, they are not designed to cope with the fine-grained and complex color patterns of multimedia applications, leading to high bandwidth requirements and an irresponsive user interface. In this article, a hybrid remote display protocol approach is presented. The existing Remote FrameBuffer protocol of Virtual Network Computing (VNC-RFB) protocol is leveraged with a video streaming mode to transport the rendered images of multimedia applications to the client. Dependent on the amount of motion in the images to be presented, the images are relayed to the client either through the VNC-RFB protocol or through video streaming in the H.264 format. The architecture of this hybrid image renderer is presented and the implementation is detailed. Furthermore, the decision heuristic to switch between the VNC-RFB and the streaming mode is discussed. Experimental results clearly show the advantage of the hybrid approach in terms of client CPU and bandwidth requirements.

Support vector machine versus logistic regression modeling for prediction of hospital mortality in critically ill patients with haematological malignancies

BackgroundSeveral models for mortality prediction have been constructed for critically ill patients with haematological malignancies in recent years. These models have proven to be equally or more accurate in predicting hospital mortality in patients with haematological malignancies than ICU severity of illness scores such as the APACHE II or SAPS II [1]. The objective of this study is to compare the accuracy of predicting hospital mortality in patients with haematological malignancies admitted to the ICU between models based on multiple logistic regression (MLR) and support vector machine (SVM) based models.Methods352 patients with haematological malignancies admitted to the ICU between 1997 and 2006 for a life-threatening complication were included. 252 patient records were used for training of the models and 100 were used for validation. In a first model 12 input variables were included for comparison between MLR and SVM. In a second more complex model 17 input variables were used. MLR and SVM analysis were performed independently from each other. Discrimination was evaluated using the area under the receiver operating characteristic (ROC) curves (± SE).ResultsThe area under ROC curve for the MLR and SVM in the validation data set were 0.768 (± 0.04) vs. 0.802 (± 0.04) in the first model (p = 0.19) and 0.781 (± 0.05) vs. 0.808 (± 0.04) in the second more complex model (p = 0.44). SVM needed only 4 variables to make its prediction in both models, whereas MLR needed 7 and 8 variables in the first and second model respectively.ConclusionThe discriminative power of both the MLR and SVM models was good. No statistically significant differences were found in discriminative power between MLR and SVM for prediction of hospital mortality in critically ill patients with haematological malignancies.

Cloud-Based Desktop Services for Thin Clients

Cloud computing and ubiquitous network availability have renewed peoples interest in the thin client concept. By executing applications in virtual desktops on cloud servers, users can access any application from any location with any device. For this to be a successful alternative to traditional offline applications, however, researchers must overcome important challenges. The thin client protocol must display audiovisual output fluidly, and the server executing the virtual desktop should have sufficient resources and ideally be close to the users current location to limit network delay. From a service provider viewpoint, cost reduction is also an important issue.

Clos lives on in optical packet switching

While the technological evolution since C. Closs seminal article (see Bell Sys. Tech. J., vol.32, p.406-24, 1953) on multistage switch architectures has been huge, his work and ideas still live on. We discuss node architectures for optical packet switching and show how the multistage approach proposed by Clos can be adopted to solve scalability issues and construct switches with large port counts. As in the old days, the driving factors behind the introduction of multistage concepts also include economic issues: compared to a single-stage architecture, the number of components to realize the switching fabric is reduced.