Visualisations can be an invaluable help for educators and students in communicating computer science concepts. Unfortunately, the availability and accessibility of visualisations and their creation are lacking. Many existing tools are either outdated, unmaintained and/or distributed as Java applets, or specialise in specific areas of computer science (most commonly algorithms and data structures). Nevertheless, access to a good-quality visualisation of a concept can greatly benefit the education process. Most computer science concepts are not particularly complicated to implement, at least a simple model implementation would not be, but are much more difficult to explain. In this paper we present ‘Visual Machine’, a new system for visualising the execution of running programs, which should enable educators to create powerful and tangible visualisations for computer science education. By specialising in exactly what is interesting about the given implementation, this system can be adapted to anything from sorting algorithms to high-level concepts such as routing algorithms in a computer network or scheduling algorithms in an operating system. This system is driven by a key concept: The visualisations created have an actual, albeit simplified, implementation of the concept being taught running in the background.

The Device-to-Device (D2D) communication has attracted much popularity in the recent years. D2D communication requires a multi-hop route to establish the communication between D2D users which are not in the communication range of each other. D2D users communicate at lower power to keep the interference to a minimum level which necessitates the need of an interference aware routing scheme. The existing interference-aware routing schemes for D2D communications either consider observed average interference or Signal-to-Interference-and-Noise-Ratio (SINR). However, to the best of our knowledge, there is no scheme in the literature that satisfies the network requirements of having better SINR and minimum interference simultaneously. In this paper, we propose a novel routing metric and novel route discovery mechanisms for D2D communication. The novel routing metric, MIIS (Metric for Interference Impact and SINR) selects routes with higher SINR and lower interference. The novel route discovery mechanism, reactive centralized routing, takes advantage of the presence of BS to establish D2D routes which reduces routing overhead as compared to distributed routing scheme. We also extend the reactive centralized routing to proactive centralized routing. The performance evaluation in OMNeT++ network simulator verifies that our proposed schemes outperform other schemes in terms of average hop count, routing overhead, packet loss ratio and end-to-end delay.

We discuss a modular simulation framework to investigate the energy efficiency of different routing protocols used in resource constrained wireless sensor networks. Our simulation framework provides a flexible tool to build diverse protocols by combining existing building blocks at different layers and to analyse how several factors such as routing strategies, MAC protocols, link and node failures, energy on path, network topology changes, in-network processing, scheduling at MAC layer and other adjustable configuration parameters influence the energy efficiency of the protocol. The simulator extends the open source OMNeT++ and its mobility framework and provides a framework to rapidly develop, to experiment with and to evaluate efficiently routing protocols; the quantitative effort to design new routing protocols and to integrate them into a complete protocol stack is considerably reduced. Moreover, we develop complete modules for MAC and network protocols; in order to study and evaluate the behavior and lifetime of the network we implement independent energy and statistics modules. We provide also new features such as add/delete, move, dis/reconnect nodes during simulation, which allow to analyse the impact of dynamic topology changes.

A basic requirement for computational steering of Grid jobs and for other interactive applications is a reliable and secure connection to the Grid job. If the Grid job is submitted by a resource broker the target host may be unknown, placed in a private IP network, and/or protected by firewalls. This paper analyses possible Grid site configurations that affect the establishment of a communication channel and classifies different scenarios. Mechanisms to establish a secure Grid connection to the remote job are described for each scenario. Security issues for the user and the administrator are identified that arise from the different ways to establish a connection. The implementation of the communication channel of RMOST (Result Monitoring and Online Steering Tool) is described. The throughput, response time, and the connection time are evaluated in dependence of the different scenario types and security levels.

Abstract Debuggers play an important role in developing parallel applications. They are used to control the state of many processes, to present distributed information in a concise and clear way, to observe the execution behavior, and to detect and locate programming errors. More sophisticated debugging systems also try to improve understanding of global execution behavior and intricate details of a program. In this paper we describe the design and implementation of SPiDER, which is an interactive source‐level debugging system for both regular and irregular High‐Performance Fortran (HPF) programs. SPiDER combines a base debugging system for message‐passing programs with a high‐level debugger that interfaces with an HPF compiler. SPiDER, in addition to conventional debugging functionality, allows a single process of a parallel program to be expected or the entire program to be examined from a global point of view. A sophisticated visualization system has been developed and included in SPiDER to visualize data distributions, data‐to‐processor mapping relationships, and array values. SPiDER enables a programmer to dynamically change data distributions as well as array values. For arrays whose distribution can change during program execution, an animated replay displays the distribution sequence together with the associated source code location. Array values can be stored at individual execution points and compared against each other to examine execution behavior (e.g. convergence behavior of a numerical algorithm). Finally, SPiDER also offers limited support to evaluate the performance of parallel programs through a graphical load diagram. SPiDER has been fully implemented and is currently being used for the development of various real‐world applications. Several experiments are presented that demonstrate the usefulness of SPiDER. Copyright © 2002 John Wiley & Sons, Ltd.

Advanced processor and machine architectures need optimizing compilers to be efficiently programmed in high level languages. Therefore the need for source level debuggers that can handle optimized programs is rising. One difficulty in debugging optimized code arises from the problem to determine the values of source code variables. To ensure correct debugger behaviour with optimized programs, the debugger not only has to determine the variable's storage location or associated register. It must also verify that the variable is current, i.e. the value determined from that location is really the value that the variable would have in unoptimized code. We will deduce requirements on algorithms for currentness determination and present an algorithm meeting this requirements that is more general than previous work. We will also give first experiences with an implementation. To our knowledge this is the first implementation of a currentness determination algorithm for globally optimized code.