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The author's experiences over a span of more than 50 years are characterised as a journey. Early interests in computer system performance modelling, information storage and retrieval, and computer networks become secondary to research topics in computer simulation. Organisations, events, and, most important, people define the paths, waysides, excursions, side roads, and major stops along the way. Editorial positions constitute an enduring thread throughout the journey. Capturing and preserving the history of the modelling and simulation discipline, frequently a topical sojourn, emerges as a dominant activity in the latter years. Two evocative questions, based on the prediction of a prominent computing pioneer, conclude the paper. 1955 Oldsmobile Starfire (98 Convertible) [ABSTRACT FROM AUTHOR]

Ant Colony Optimization (ACO) is a popular optimal algorithm, whose typical application is to solve Travel Salesman Problem (TSP). The time complexity of ACO is O(mN t), where the parameters m, N and t denote the number of ants, cities and iteration steps, respectively. Improving running speed is an important research focus, and reducing the parameter N and t is an effective way. Especially, reducing the parameter N is an efficient method. In this paper, we present a new clustering algorithm named Vertex Coloring Clustering (VCC), which uses the thought of vertex coloring to classify all cities into some classes and lets ACO act on each class to get local TSP routes, and joins these local routes as a whole route. Owing to Vertex Coloring has property that the number of color is the minimum, the minimum number of classes is obtained in this paper. Each class can be considered as a smaller TSP. So, when ACO algorithm calculate the local route on each class obtained by VCC algorithm, the parameter N and the iteration number t are reduced. The simulation shows that the improved ACO by VCC is faster than the ACO algorithm which uses algorithm Ant-Cycle by factors of 15-750. [ABSTRACT FROM AUTHOR]

Energy optimisation is one of the important issues in the research of wireless sensor networks (WSNs). In the application of monitoring, a large number of sensors are scattered uniformly to cover a collection of points of interest (PoIs) distributed randomly in the monitored area. Since the energy of battery-powered sensor is limited in WSNs, sensors are scheduled to wake up in a large-scale sensor network application. In this paper, we consider how to reduce the energy consumption and prolong the lifetime of WSNs through wake-up scheduling with probabilistic sensing model in the large-scale application of monitoring. To extend the lifetime of sensor network, we need to balance the energy consumption of sensors so that there will not be too much redundant energy in some sensors before the WSN terminates. The detection probability and false alarm probability are taken into consideration to achieve a better performance and reveal the real sensing process which is characterised in the probabilistic sensing model. Data fusion is also introduced to utilise information of sensors so that a PoI in the monitored area may be covered by multiple sensors collaboratively, which will decrease the number of sensors that cover the monitored region. Based on the probabilistic model and data fusion, minimum weight probabilistic coverage problem is formulated in this paper. We also propose a greedy method and modified genetic algorithm based on the greedy method to address the problem. Simulation experiments are conducted to demonstrate the advantages of our proposed algorithms over existing work. [ABSTRACT FROM AUTHOR]

The radio frequency identification (RFID) technology has gained a lot of recent interests because it has been widely recognised as a foundation technology for the ‘Internet of things’. In current multi-reader RFID systems, readers work with fairly less cooperation and are responsible to retrieve data from different number of tags individually, which results in large reading time of obtaining all tag data. In this paper, a fast tag reading problem in multi-reader RFID systems with the goal of obtaining all tag data by using minimum reading time is studied. A distributed load-balancing algorithm based on diffusion method is proposed to solve the problem by migrating tags from highly loaded reader to lightly loaded reader. The simulation results demonstrate the effectiveness and efficiency of proposed algorithm. [ABSTRACT FROM AUTHOR]

Acoustic waves are the preferred medium for long-range underwater communications. Increasing number of innovative methods for underwater communication using acoustic waves appears. Performance of underwater communications for the new methods needs to be evaluated through simulation. Simulation of underwater acoustic communications is challenging due to many impediments, including attenuation, multipath propagation, noise and Doppler spread. In this paper, a baseline time domain simulation model is extended to several frequency-domain models. The proposed frequency models, including two incoherent models and a coherent model, take multipath attenuation and ambient noise into account. An incoherent linear fitting model and a coherent model are simulated and compared with a theoretical reference and the baseline time model. The proposed incoherent models are also compared with one another. Simulation shows that the incoherent linear fitting model produces results similar to the multi-frequency-merge-path model, but requires less computation time. In addition, the proposed coherent model is compared with field experimental data. The coherent model with color noise, in the frequency domain, can match closely the bit error rates of the field experimental data. In this paper, several models are proposed and compared considering multipath attenuation and ambient noise. The models in the time domain and frequency domain all take into account the attenuation calculation along with white and colored noise. In the time domain, a classic baseline model is presented. In the frequency domain, not only incoherent but also coherent attenuation are proposed and implemented. Incoherent means that the interference created by these phase differences is ignored. Coherent refers that the phase differences of signals propagating through different paths are taken into account. White noise is modeled as traditional Additive white Gaussian noise. Colored noise makes the white noise go through a low-pass filter with a profile similar to the one of the underwater ambient noise. The bit error rate versus energy per bit to noise power spectral density ratio Eb/N0 is applied for evaluation. The simulations are implemented using MATLAB and the BELLHOP tracing program. [ABSTRACT FROM AUTHOR]

Nowadays various chaotic secure communication systems based on synchronization of chaotic circuits are widely studied. To achieve synchronization, the control signal proportional to the difference between the circuits signals, adjust the state of one circuit. In this paper the synchronization of two Chua circuits is simulated in Simulation Programs with Integrated Circuit Emphasis. It is shown that the choice of control signal is not straightforward, especially in the case of multistability and hidden attractors. [ABSTRACT FROM AUTHOR]

Energy efficiency and Quality of Service (QoS) providing are known to be critical design concerns in routing protocols for Wireless Sensor Networks (WSNs). Recent studies, demonstrate that Opportunistic Routing (OR) can greatly improve the performance of WSNs by exploiting the broadcast nature of the wireless medium. In this paper, we propose a new QoS aware and Energy efficient Opportunistic Routing protocol (QEOR) to efficiently routing data under QoS and energy constraints for WSNs. QEOR uses a new multi-metric QoS based candidate selection method in order to accurately select and prioritise the candidate forwarders. The selection is focused on a QoS function that takes into consideration the reliabilty of buffers and links, while the prioritisation is established according to transmission delays. To achieve an obvious improvement on the energy consumption, QEOR uses an energy efficient coordination method and an implicit ACKnowledgement scheme for collision and redundancy avoidance. Simulation results show that QEOR provides best performances as compared to other OR protocols. [ABSTRACT FROM AUTHOR]

In a networked control system, several nodes exchange information through a network, to achieve specific control goals and thus increasing network traffic. This affects the overall system performance. Several approaches try to satisfy requirements of both control and communication performance. Particularly, some methodologies have been proposed to save bandwidth. One of such methodologies has been scheduling, which has been studied in depth through the last decade. Commonly, the objective of using scheduling to save bandwidth is to accurately use the computing resources. This paper shows two scheduling strategies, one performing static scheduling and the other carrying out dynamic scheduling, in order to expose the advantages of using dynamic scheduling in an ad hoc implementation. Both strategies execute on a real-time distributed system, and both are able to modify the frequency of transmission as well as the periods of tasks in individual components. Hence, both of them tend to impact on the quality of performance of the system, due to network use. The first scheduling strategy modifies the periods of task, and network access is assigned through a static scheduling algorithm. On the other hand, the second strategy, schedulability, is dynamically achieved by controlling the rate of frequency transmission into a frequency region, bounded by minimum and maximum transmission rates. Numerical simulations are used as implementations of both strategies. [ABSTRACT FROM PUBLISHER]

The use of frequency hopping spread spectrum in Bluetooth significantly differentiates its networks from classical radio networks. In order to observe such differences, we studied basic algorithms, in particular neighbour discovery and message exchange algorithms. Some of the major differences are found in the procedures of device discovery and link establishment, which are studied in this paper. We focus on their impact on Bluetooth networks' distributed algorithms. We show through detailed simulation experiments that minor modifications to the Bluetooth specifications or their implementation may significantly affect the performance of well-known neighbour discovery algorithms. We then study the impact of the procedures of link establishment with the purpose of finding time-efficient implementations of communication rounds for Bluetooth networks. We study OrderedExchange and RandomExchange as both algorithms implement communication rounds in Bluetooth, but use the PAGE and PAGE SCAN states differently. Theoretical analysis shows that RandomExchange has a better time complexity, while simulation experiments show that OrderedExchange significantly outperforms RandomExchange in networks with a practical size (110 nodes and less). We use the previous results to improve the time efficiency of Bluetooth scatternet formation algorithms through the introduction of the time-efficient algorithm OrderedExchangeCMIS. We believe that the study of some other basic algorithms (such as broadcasting, spanningtree and election) will lead to a better understanding of Bluetooth networks, and as a consequence, to more efficient algorithms that fully leverage the strength of this type of network. [ABSTRACT FROM PUBLISHER]

Contemporary networks support multiple priorities, aiming to differentiate the quality of service (QoS) levels offered to individual traffic classes. Support for multiple priorities necessitates the introduction of a scheduling algorithm, to select each time the next packet to transmit over the data link. Class-based weighted fair queuing (CBWFQ) scheduling and its variations are widely used as a scheduling technique since it is easy to implement and prevent the low-priority queues from starvation, i.e. receiving no service during periods of high-priority traffic. CBWFQ effectively thus offers low-priority queues, the opportunity to transmit packets even though the high-priority queues are not empty. In this paper, we present the modelling and performance evaluation of a single-buffered, four-priority multistage interconnection network (MIN) operating under the CBWFQ scheduling policy. Performance evaluation is conducted through simulation, and the performance metrics obtained can be used by MIN designers to set the appropriate queue weights according to the expected traffic and the desired QoS levels for each priority class, delivering efficient thus systems. [ABSTRACT FROM AUTHOR]

Contiguous allocation in multicomputers is useful for security and accounting reasons. In mesh-connected systems, each job is allocated an exclusive submesh of processors, and the allocated submesh has the same shape and size as that requested by the job. Because of this size and shape constraint, contiguous allocation typically suffers from high processor fragmentation. Processor fragmentation can be reduced by considering contiguous allocation to all possible request shapes, while maintaining contiguity. However, request shape modification can influence communication overhead. In this paper, we study the effect of request shape modification on communication overhead and performance in 2D mesh-connected multicomputers, where several common communication patterns are simulated in detail. The simulation results based on both synthetic and real workload models show that permitting all request shape changes can improve system performance substantially. For example, it improves the performance of first-fit allocation by up to about 60% in terms of average job turnaround time. [ABSTRACT FROM AUTHOR]

It is known that there exist computational problems that can be solved on a parallel computer, yet are impossible to be solved sequentially. Specifically, no general purpose sequential model of computation, such as the Turing machine or the random access machine, can simulate a large family of computations (e.g. solutions to certain real-time problems), each of which is capable of being carried out readily by a particular parallel computer. We extend the scope of such problems to the class of problems with uncertain time constraints. The first type of time constraints refers to uncertain time requirements on the input data, that is when and for how long are the input data available. The second type of time constraints refers to uncertain deadlines on when outputs are to be produced. Our main objective is to exhibit computational problems in which it is very difficult to find out (read ‘compute’) what to do and when to do it. Furthermore, problems with uncertain time constraints, as described here, prove once more that it is impossible to define a ‘universal computer’, that is a computer able to perform (through simulation or otherwise) all computations that are executable on other computers. Finally, one of the contributions of this paper is to promote the study of a topic, conspicuously absent to date from theoretical computer science, namely the role of physical time and physical space in computation. The focus of our work is to analyse the effect of external natural phenomena on the various components of a computational process, namely the input phase, the calculation phase (including the algorithm and the computing agents themselves) and the output phase. [ABSTRACT FROM AUTHOR]

In mobile ad hoc network (MANET), the issues such as limited bandwidth availability, dynamic connectivity and so on cause the process of intrusion detection to be more complex. The nodes that monitor the malicious nodes should have necessary residual bandwidth and energy and should be trustable. In order to overcome these drawbacks, in this paper, we propose a swarm-based efficient distributed intrusion detection system for MANET. In this technique, swarm agents are utilised to select the nodes with highest trust value, residual bandwidth and residual energy as active nodes. Each active node monitors its neighbour nodes within its transmission range and collects the trust value from all monitored nodes. The active nodes adaptively change as per the trust thresholds. Upon collaborative exchange of the trust values of the monitored nodes among the active nodes, if the active node finds any node below a minimum trust threshold, then the node is marked as malicious. When the source receives alert message about the malicious node, a defence technique is deployed to filter the corresponding malicious node from the network. By simulation results, we show that the proposed approach is efficient intrusion detection mechanism for MANET. [ABSTRACT FROM AUTHOR]

The Session Initiation Protocol (SIP) retransmission mechanism can cause SIP network collapse with short-term overload. In this paper, we investigate with a fluid modelling approach the chaotic behaviour of the SIP retransmission mechanism in SIP networks. We capture the complex correlation structure in SIP systems through a detailed and novel queuing analysis. To dimension a buffer size which can avoid unnecessary message drop in a SIP server, we develop a sufficient condition for a stable SIP system analytically based on our fluid model. We also apply our fluid model to the simulation of a complex SIP system. We compare the simulation results achieved through our fluid models with those based on OPNET®event-driven approach to demonstrate the validity of our approach. [ABSTRACT FROM AUTHOR]

Rapid penetration of smart wireless devices and enormous growth of wireless communication technologies have already led to the deployment of wireless sensor networks (WSNs). Sensor nodes in these networks severely suffer from resource constraints, such as energy, buffer, bandwidth and so on. On the other hand, with increasing demand for real-time services in WSN applications, quality of service (QoS)-based routing has emerged as an interesting research topic. Naturally offering some QoS-guarantee in sensor networks raises significant challenges. The networks need to cope up with resource constraints, while providing precise QoS (end-to-end delay and reliability requirement) guarantee. This paper presents QoS aware routing protocol, namely the energy–buffer aware reliable routing (EBARR) protocol that meets both challenges of reliability and timely delivery of critical data. The EBARR achieves reliability by prioritising the packet transmission, reserving the energy and employing efficient buffer management policy to mitigate packet losses due to buffer overflow, hop-by-hop flow control mechanism to reduce packet retransmission overheads along multi-hop routes from source to sink. An angle-based router set ensures the delivery of data within the maximum tolerable time. We evaluate and compare the performance of EBARR protocol with the multi-constraint multi-path routing protocol by means of simulation experiments. Simulation results show that the proposed EBARR protocol efficiently mitigates critical packet losses even under heterogeneous traffic, thereby achieving required reliability and timely delivery of data. [ABSTRACT FROM AUTHOR]

Over the past few years, many algorithms have been proposed to support collective communication operations for large-scale multicomputers. When proposing any new such algorithm operation, it is critical to determine its precise scope and evaluate it with accurate modelling of the underlying routing and communication mechanisms. However, there has been comparatively little activity in the area of analytical modelling of these operations. As a result, most existing studies have relied on simulation to evaluate the performance merits of collective communication algorithms. This paper presents a new analytical model for predicting broadcast latency in the wormhole-routed torus, which is one of the most common networks used in multicomputers. The broadcast algorithm considered in this study is based on the Bose's broadcast algorithm [Bose, B., Broeg, B., Younggeun, K. and Ashir, Y., 1995, Lee distance and topological properties of k -ary n -cubes, IEEE Transaction on Computers , 44 (8), 1021–1030]. Results obtained through simulation experiments show that the model exhibits a good degree of accuracy in predicting message latency under different working conditions. [ABSTRACT FROM AUTHOR]

Cooperative trajectory mapping is an emerging technique that allows users to create such a map by using data that are collected from each other's mobile phones. This technique has been proposed for many applications, such as people localisation, public transportation tracking and traffic monitoring. Unlike the traditional Global Positioning System, cooperative trajectory mapping only requires information about the departure distance and moving direction from the previously reported position. This avoids problems such as the high-energy consumption of GPS and weak GPS signals in indoor conditions. However, the new technique also brings about other problems, such as measurement errors in cooperative trajectory mapping, which is when a measurement error causes the spatial relations among users to be wrong. We propose an encounter-based error correction algorithm to efficiently reduce measurement errors. Extensive simulation experiments are carried out to validate our solutions. [ABSTRACT FROM AUTHOR]

Logical gates are constructed based on a method of numerical modeling of natural erosion of sandstone. Values of logical variables are determined by the presence of sandstone. The presence of sandstone corresponds to the logical value of True, whereas the absence of material corresponds to the False value. Logical functions are computed through the formation of sandstone structures at action of natural erosion where loading conditions are specified. AND and XOR gates and a one-bit binary half-adder are implemented. [ABSTRACT FROM AUTHOR]

We present a Python extension to the massively parallel HPC simulation toolkitwaLBerla.waLBerlais a framework for stencil based algorithms operating on block-structured grids, with the main application field being fluid simulations in complex geometries using the lattice Boltzmann method. Careful performance engineering results in excellent node performance and good scalability to over 400,000 cores. To increase the usability and flexibility of the framework, a Python interface was developed. Python extensions are used at all stages of the simulation pipeline: they simplify and automate scenario setup, evaluation, and plotting. We show how our Python interface outperforms the existing text-file-based configuration mechanism, providing features like automatic nondimensionalization of physical quantities and handling of complex parameter dependencies. Furthermore, Python is used to process and evaluate results while the simulation is running, leading to smaller output files and the possibility to adjust parameters dependent on the current simulation state. C++ data structures are exported such that a seamless interfacing to other numerical Python libraries is possible. The expressive power of Python and the performance of C++ make development of efficient code with low time effort possible. [ABSTRACT FROM AUTHOR]

The wasteful consumption of freshwater in heavily populated coastal areas usually consist the basic reason for the intrusion of saltwater into the coastal aquifers. In order to avoid such catastrophic scenarios, their prediction is of utter significance. Underground water systems are highly complex and the water flow is extremely dynamic, thus making the prediction of this phenomenon a difficult task. For this reason, a two dimensional Cellular Automaton (CA) was designed enabling both the qualitative and quantitative simulation and illustration of the saltwater intrusion into an unconfined coastal aquifer. The presented results ensure the robustness of the proposed CA model taking full advantage of its inherent parallelism and local connectivity. [ABSTRACT FROM AUTHOR]

Two parallel computer paradigms available today are multi-core accelerators such as the Sony, Toshiba and IBM Cell or Graphics Processing Unit (GPUs), and massively parallel message-passing machines such as the IBM Blue Gene (BG). The solution of systems of linear equations is one of the most central processing unit-intensive steps in engineering and simulation applications and can greatly benefit from the multitude of processing cores and vectorisation on today's parallel computers. We parallelise the conjugate gradient (CG) linear equation solver on the Cell Broadband Engine and the IBM Blue Gene/L machine. We perform a scalability analysis of CG on both machines across 1, 8 and 16 synergistic processing elements and 1–32 cores on BG with heptadiagonal matrices. The results indicate that the multi-core Cell system outperforms by three to four times the massively parallel BG system due to the Cell's higher communication bandwidth and accelerated vector processing capability. [ABSTRACT FROM AUTHOR]

Electric vehicle (EV) charging must be optimised for grid load while guaranteeing that drivers' schedules and range requirements are met. A system encompassing EV owner input via a mobile application, an aggregation middleware, a charge scheduling and vehicle-to-grid (V2G) operation algorithm and a radio-frequency identification reader is proposed. The algorithm's parameters and effectiveness are presented and discussed using simulation results. Simulation results show the algorithm to effectively optimise charging and V2G operation for a given electricity price curve. The proposed system is shown to alleviate grid load during peak hours, take advantage of off-peak charging benefits and generate revenue for the parking garage operator. [ABSTRACT FROM PUBLISHER]

Our goal is to predict the performance of multi-node systems consisting of identical processing nodes from single node profiles. The performance of multi-node systems that have coherent caches considerably depends on coherence overhead, which is roughly in direct proportion to the number of transfers of cached copies. We analytically model the number of transfers of cached copies of a data block per write access for random accesses where multi-node systems have multi-versioned coherence mechanisms. Our model aims at helping to predict a baseline performance when closed and/or complex business applications are running, such as clustered databases, the algorithmic behaviours of which are practically impossible to analyse and characteristics of which vary from system to system. To empirically verify our analytical model and show how coherence overhead varies in accordance with parameters, we compared the number of transfers that was predicted by our model and that was counted by a toy simulator of multi-versioned mechanisms. [ABSTRACT FROM AUTHOR]

We present an optimistic approach for consistent, interactive steering of distributed computations. In contrast to conservative approaches, the optimistic steering approach assumes that next steerable points are consistent and invokes steering updates without concern for the state of any other process. This approach is expected to perform well since it eliminates the need for blocking processes. Furthermore, we introduce a novel transaction-based computation model. We view the local computation of a process as a sequence of local transactions and a distributed computation as a set of partially ordered global transactions. This abstraction not only gives users a simple and high-level view of distributed computation, but also simplifies reasoning about consistency problems by reducing the amount of information to be handled. Using the Higher KdV (HiKdV) equation simulation program, we evaluate the performance of the optimistic steering approach. Our experiments show that when the percentages of consistency on the first attempt are large enough, the optimistic approach will achieve better performance; otherwise, the conservative approach will be better. [ABSTRACT FROM AUTHOR]

A novel internet multicast routing protocol is presented to possess efficiency and effectiveness for multicast packet routing with short delay, high throughput, resource utilization and scalability for a single multicast group g . The protocol has two features: (1) Multiple Shared-Trees (MST) are configured to provide efficient, dynamic and quality multicast routing; (2) Anycasting approach is applied by forming the tree roots into an anycast group so that the multicast packets can be anycast to the nearest node at one of the shared trees to achieve the best routing service for the packets. The performance of the MST protocol is analyzed through extensive simulations and compared with well-known source tree and shared-tree routing. [ABSTRACT FROM AUTHOR]