Model of joint servicing of real-time service traffic and data traffic. II

For the model of joint servicing of the real-time service and data traffics, numerical study of the demand servicing indices vs. the model input parameters was carried out. Solution of the problem of estimating the minimal channel resource sufficient to service the demand inflow with the desired performance was considered. Approximate algorithms to calculate the model were constructed, and their accuracy was analyzed numerically.     

Performance analysis of banyan-type multistage interconnection networks under nonuniform traffic pattern

Multistage Interconnection Networks(MINs) have a number of applications in the areas of computer and communications. The most widely researched structure among MIN’s is the (l)banyan type network. It has several variations such as buffered banyan, batcher-banyan, tandem banyan, recirculating banyan and banyan with contention resolution phase. Analytical performance evaluation is crucial for justifying the merit of the design in different operational conditions. While several analytical models have been proposed for the performance evaluation of MINs, they are mainly for uniform traffics. Even the models for nonuniform traffics have several shortcomings such as they only consider output buffered structure or do not consider blocking conditions. In this paper, the more accurate models than any other ones so far have been proposed for the performance evaluation of multibuffered banyan-type MIN’s under nonuniform traffic condition is obtained. The accuracy of proposed models are conformed by comparing with the results from simulation. Firstly, single buffer model is developed. Markov chain is used for the analysis. Multibuffer model is obtained from single buffer model. Simulation is performed using Discrete Evenet Simulaton(DES) method. As a results, proposed model proves to be very accurate.     

Queuing analysis of shared-buffer switches with control scheme under bursty traffic

Shared-buffer switches have many advantages such as relatively low cell loss rate and good buffer utilization, and they are increasingly favoured in recent VLSI switch designs for ATM. However, their performance degrades dramatically under nonuniform traffic due to the monopolization of the buffer by some favoured cells. To overcome this, restricted types of sharing and hot-spot pushout (HSPO) have been proposed, and the latter has been shown by simulation to perform better in all situations. In this paper we develop an analytical model for performance evaluation of a shared-buffer asynchronous transfer mode (ATM) switch with HSPO under bursty traffic. This analytical model is an improved version of the first model ever developed for this purpose. We balance the relative queues to approximate the effects of pushout, while keeping only four state-variables, and our model gives a good agreement with simulation, for calculating throughput and cell loss.     

Managing emergencies and abnormal situations in air traffic control (part II): Teamwork strategies

Team performance has been studied in many safety-critical organizations including aviation, nuclear power plant, offshore oil platforms and health organizations. This study looks into teamwork strategies that air traffic controllers employ to manage emergencies and abnormal situations. Two field studies were carried out in the form of observations of simulator training in emergency and unusual scenarios of novices and experienced controllers. Teamwork strategies covered aspects of team orientation and coordination, information exchange, change management and error handling. Several performance metrics were used to rate the efficiency of teamwork and test the construct validity of a prototype model of teamwork. This is a companion study to an earlier investigation of taskwork strategies in the same field (part I) and contributes to the development of a generic model for Taskwork and Teamwork strategies in Emergencies in Air traffic Management (T²EAM). Suggestions are made on how to use T²EAM to develop training programs, assess team performance and improve mishap investigations.     

Performance analysis of priority scheduling mechanisms under heterogeneous network traffic

Priority scheduling principle plays a crucial role in the Differentiated Services (DiffServ) architecture for the provisioning of Quality-of-Service (QoS) of network-based applications. Analytical modelling and performance evaluation of priority queuing systems have received significant attention and research efforts. However, most existing work has primarily focused on the analysis of priority queuing under either Short Range Dependent (SRD) or Long Range Dependent (LRD) traffic only. Recent studies have shown that realistic traffic reveals heterogeneous nature within modern multi-service networks. With the aim of investigating the impact of heterogeneous traffic on the design and performance of network-based systems, this paper proposes a novel analytical model for priority queuing systems subject to heterogeneous LRD self-similar and SRD Poisson traffic. The key contribution of the paper is to extend the application of the generalized Schilder's theorem (originally a large deviation principle for handling Gaussian processes only) to deal with heterogeneous traffic and further develop the analytical upper and lower bounds of the queue length distributions for individual traffic flows. The validity and accuracy of the model demonstrated through extensive comparisons between analytical bounds and simulation results make it a practical and cost-effective evaluation tool for investigating the performance behaviour of priority queuing systems under heterogeneous traffic with various parameter settings.     

Prediction of communication delay in torus networks under multiple time-scale correlated traffic

The efficiency of a large-scale multicomputer is critically dependent on the performance of its interconnection network. Current multicomputers have widely employed the torus as their underlying network topology for efficient interprocessor communication. In order to ensure a successful exploitation of the computational power offered by multicomputers it is essential to obtain a clear understanding of the performance capabilities of their interconnection networks under various system configurations. Analytical modelling plays an important role in achieving this goal. This study proposes a concise performance model for computing communication delay in the torus network with circuit switching in the presence of multiple time-scale correlated traffic which is found in many real-world parallel computation environments and has strong impact on network performance. The tractability and reasonable accuracy of the analytical model demonstrated by extensive simulation experiments make it a practical and cost-effective evaluation tool to investigate network performance with various alternative design solutions and under different operating conditions.     

FPGEN: A fast, scalable and programmable traffic generator for the performance evaluation of high-speed computer networks

Testing today’s high-speed network equipment requires the generation of network traffic which is similar to the real Internet traffic at Gbps line rates. There are many software-based traffic generators which can generate packets according to different stochastic distributions. However, they are not suitable for high-speed hardware test platforms. This paper describes FPGEN (Fast Packet GENerator), a programmable random traffic generator which is entirely implemented on FPGA (Field Programmable Gate Array). FPGEN can generate variable packet sizes and traffic with Poisson and Markov-modulated on-off statistics at OC-48 rate per interface. Our work that is presented in this paper includes the theoretical design of FPGEN, the hardware design of the FPGA-based traffic generator board (printed circuit board design and construction) and the implementation of FPGEN on FPGA. Our experimental study demonstrates that FPGEN can achieve both the desired rate and statistical properties for the generated traffic.     

Platoon dispersion prediction under the condition of adjacent cycle traffic flow overlapping based on Support Vector Regression

Coordinated signal control can improve the continuity of vehicular traffic flow movement and reduce delay. Cycle Flow Profile is the base for calculating coordinated signal control parameters. Platoon dispersion characteristic determines the Cycle Flow Profile. So, improving platoon dispersion prediction accuracy can obtain significant benefit for signal coordination. When the velocities of the vehicles vary greatly, faster vehicles of next cycle can catch up the slower vehicles of the current cycle. Traffic flow overlapping of adjacent cycle is an important characteristic. Support Vector Regression is adopted to predict platoon dispersion and compares prediction accuracy with Robertson formula. The results are encouraging; Support Vector Regression has higher prediction accuracy.     

Transient process relaxation time research under the condition of self-similar traffic input in wireless networks

In the article, the results of measuring the traffic in wireless networks are presented. The results provide evidence of the traffic being notably self-similar. The two following models were developed in order to estimate the parameters of a wireless network operating along with the input traffic being self-similar: a model for systems with no restrictions on the quantity of the orders in the system lines and a model for systems with limited buffer volumes. The two types of incoming traffic that each system was simulated for were the Poisson and self-similar traffic.The main objective of the article is to figure out the relaxation time and dependences of the relaxation time and loss probability on different parameters of the simulated systems.     

Strategies for designing distributed systems: case studies in the design of an air traffic management system

The air traffic management system in the USA is an example of a distributed problem-solving system. It has elements of both cooperative and competitive problem-solving. It includes complex organizations such as Flight Operations Centers, the FAA Air Traffic Control Systems Command Center (ATCSCC), and traffic management units at en route centers that focus on daily strategic planning, as well as individuals concerned more with immediate tactical decisions (such as air traffic controllers and pilots). The design of this system has evolved over time to rely heavily on the distribution of tasks and control authority in order to keep cognitive complexity manageable for any one individual operator, and to provide redundancy (both human and technological) to serve as a safety net to catch the slips or mistakes that any one person or entity might make. Within this distributed architecture, a number of different conceptual approaches have been applied to deal with cognitive complexity and to provide redundancy. These approaches can be characterized in terms of the strategy for distributing: (1) control or responsibility, (2) knowledge or expertise, (3) access to data, (4) processing capacity, and (5) goals and priorities. This paper will provide an abstract characterization of these alternative strategies for distributing work in terms of these 5 dimensions, and will illustrate and evaluate their effectiveness in terms of concrete realizations found within the National Airspace System.     

From trees to forest: relational complexity network and workload of air traffic controllers

In this paper, we propose a relational complexity (RC) network framework based on RC metric and network theory to model controllers' workload in conflict detection and resolution. We suggest that, at the sector level, air traffic showing a centralised network pattern can provide cognitive benefits in visual search and resolution decision which will in turn result in lower workload. We found that the network centralisation index can account for more variance in predicting perceived workload and task completion time in both a static conflict detection task (Study 1) and a dynamic one (Study 2) in addition to other aircraft-level and pair-level factors. This finding suggests that linear combination of aircraft-level or dyad-level information may not be adequate and the global-pattern-based index is necessary. Theoretical and practical implications of using this framework to improve future workload modelling and management are discussed.     

A Model of Inventory Control. II

A model of inventory control is considered. It is described by a semi-Markovian random walk with a negative drift at an angle of (0° < < 90°), with positive random jumps, delays, and absorbing screens at zero and at a #gt; 0. The Laplace transformation is found for the distribution of the first moment of the stoking up of a warehouse, and its first and second moments are explicitly obtained.     

MARKTRAN II: An interactive FORTRAN program for calculating markov transition probabilities of two-dimensional patterns

MARKTRAN II is an interactive FORTRAN IV program that computes Markov transition probabilities for two-dimensional patterns. The pattern is represented by a series of discrete states at each point on a rectangular grid composed of square cells. Transition probabilities in eight directions are computed. MARKTRAN II is useful for numerically describing the fabric of patterns that possess any degree of anisotropy. Geological applications include analysis of rock fabrics, outcrop patterns of geological maps, and variations in ore grade expressed as discrete states.     

Challenges of developing the complex socio-technical system: realising the present, acknowledging the past, and envisaging the future of vessel traffic services

This paper raises the question of how to guide the development of an emerging complex socio-technical system. The empirical basis for the discussion is a study of Vessel Traffic Services (VTS). We analysed the current state and the history of the service in Finland in four studies and identified several development needs. The results showed that there are differences between the outcome, practices and conceptions of the core task across different experts in the VTS centres, which can be explained by the current state of the constituents and the history of the activity system. Qualitatively different development phases characterised either by a top-down standardisation or bottom-up construction process were recognised. A combination of these processes was suggested for the future development strategy of the VTS. This could allow both continuous development within VTS and recognition of the need for a new system. A promising way to achieve continuous development is by creating reflective practices supported for instance with annual simulator exercises aimed at procedure development. We conclude that solving the current problems and promoting the development of the complex system call for a dynamic, open vision of the target future of the system, in which the pressures from the social, political and technological environments are taken into account. The results of ergonomics studies can help in self-reflecting, envisaging and developing supportive methods for the system but the persons within the system create the will to develop and find their way towards the development horizon.     

An Agent-Based Microsimulation Model of Swiss Travel: First Results

In a multi-agent transportation simulation, each traveler is represented individually. Such a simulation consists of at least the following modules: (i) Activity generation. (ii) Modal and route choice. (iii) The traffic simulation itself. (iv) Learning and feedback. In order to find solutions which are consistent between the modules, a relaxation technique is used. This technique has similarities to day-to-day human learning.Using advanced computational methods, in particular parallel computing, it is now possible to run such a system for large metropolitan areas with 10 million inhabitants or more. This paper reports on such a simulation system for all of Switzerland. Our focus is on a computationally efficient implementation of the agent-based representation, which means that in fact each agent is represented with an individual set of plans as explained above. A database is used to store the agents' strategies, which are loaded into the simulation modules as required; the modules then feed back individual performance measures into the database. This approach allows that additional modules can be coupled easily, and without degrading computational performance.The set-up was tested for Swiss morning peak traffic. Hourly demand matrices were taken from work with the VISUM assignment package and converted to our needs. Routes were assigned via feedback learning using the agent data base. In other words, the current implementation uses a car-only versions of the modules (ii), (iii), and (iv). Resulting flow volumes are compared to the VISUM assignment results, and to field data.     

Scheduling of wireless control networks based on IEEE 802.15.4 networks: Mixed traffic environment

This paper describes a scheduling method of wireless control networks for factory automation using IEEE 802.15.4 networks. The superframe of IEEE 802.15.4 is used for the transmission of real-time mixed data for wireless control systems. The schedulability of real-time data is defined, and scheduling algorithms are proposed for the efficient transmission of real-time mixed traffic. Simulation results show enhancements in the average network utilization and packet drop rate for real-time data.     

Hydrodynamic dispersion in long microchannels under conditions of electroosmotic circulation: II. Electrolytes

This work describes the steady-state transport of an electrolyte due to a stationary concentration difference in straight long channels under conditions of electroosmotic circulation. The electroosmotic flow is induced due to the slip produced at the charged channel walls. This flow is assumed to be compensated by a pressure-driven counterflow so that the net volume flow through the channel is exactly zero. Owing to the concentration dependence of electroosmotic slip, there is an involved coupling between the solute transfer, hydrodynamic flow and charge conservation. Nevertheless, for such a system the Taylor–Aris dispersion (TAD) theory is shown to be approximately applicable locally within an inner part of the channel for a wide range of Péclet numbers (Pe) irrespective of the concentration difference. Numerical simulations reveal only small deviations from analytical solutions for the inner part of the channel. The breakdown of TAD theory occurs within boundary regions near the channel ends and is related to the variation of the dispersion mechanism from the purely molecular diffusion at the channel ends to the hydrodynamic dispersion within the inner part of the channel. This boundary region is larger at the lower-concentration channel edge and its size increases nearly linearly with Pe number. It is possible to derive a simple analytical approximation for the inner profile of cross-section-averaged electrolyte concentration in terms of only few parameters, determined numerically. Such analytical approximations can be useful for experimental studies of concentration polarization phenomena in long microchannels.     

Cellular Automata Simulations of Traffic: A Model for the City of Geneva

This paper proposes a micro-simulation based on a simple cellular automata model to analyze and describe the traffic of cars in the city of Geneva. We consider a road network containing the most important roads in the city center and its suburbs. As many as 1066 street junctions are considered, for a total network length of about 4000 km. Our simulation reproduces the rush hour period, based on real data involving around 85000 vehicles. The main properties we study concern the average travel time and its fluctuation of various routes, as a function of the departure time. Finally we briefly discuss the computer implementation of our model and its performance on a parallel computer.