No / Traffic congestion arising from the shared nature of uplink channels in wireless networks can cause serious problems for the provision of QoS to various services. One approach to overcome these problems is to implement some effective congestion control mechanisms at the downlink buffer at the mobile network link layer or at gateways on the behalf of wireless network access points. Active queue management (AQM) is an effective mechanism to support end-to-end traffic congestion control in modern high-speed networks. Initially developed for Internet routers, AQM is now being also considered as an effective congestion control mechanism to enhance TCP performance over 3G links. This paper proposes an analytical performance model for AQM using various dropping functions. The selection of different dropping functions and threshold values required for this scheme plays a critical role on its effectiveness. The model uses a well-known Markov-modulated Poisson process (MMPP) to capture traffic burstiness and correlations. The validity of the model has been demonstrated through simulation experiments. Extensive analytical results have indicated that exponential dropping function is a good choice for AQM to support efficient congestion control.

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / Powered by single-segment switched interconnection, Ethernet can be used in time-critical data acquisition applications. Unlike synchronous time division multiple access, asynchronous packet streams result in congestions and uncertain multiplexing delays. With the delay analysis in the worst case and probabilistic guaranteeing conditions, we restrict the packet-sizes, intervals or traffic burstiness a priori to regulate delay deviations within acceptable scales. Some methods of combinatorics and stochastic theory, e.g. Cumulant Generating Function and the Large Deviation Principle, are used and verified by some simulation-based computations. The influence of time varying delay for telemetry applications is also discussed in some sense.

Thesis (MBA)--Stellenbosch University, 1999. / ENGLISH ABSTRACT: A mini-study project presented on the use of Microsoft Excel 2000 in the field of simulation. The mini-study project covers the principles of queuing and it’s outputs. The simulation model will test various scenario’s of queuing theory. Inputs can be changed to suit the users requirements. Results may be analysed to determine an optimal queuing environment. / AFRIKAANSE OPSOMMING: Hierdie mini-werkstuk illustreer die gebruik van Excel 2000 in die veld van simulasie. Die beginsels van toustaan modelle word gedek, asook die tipiese resultate. Die simulasiemodel modelleer en toets verskillende toustaan scenarios. Toevoere kan verander word na gelang van die gebruiker se keuse. Die resultate kan ontleed word om die optimale toustaan omgewing te bepaal.

Darbe bus nagrinėjama mišraus tipo masinė aptarnavimo sistema, kurią gali sudaryti n paraiškų šaltinių, su atitinkamais paprasčiausių srautų intensyvumais, o paraiškos gali būti paskirstomos į m aptarnavimo įrenginių su fiksuotomis prioritetinėmis paraiškų eilėmis, kur paraiškos aptarnavimo laikas S yra pasiskirstęs pagal apibendrintą tikimybinio skirstinio funkciją G(t). Darbo tikslas – sukurti programinę įrangą, kuri pagal pateiktą sistemos funkcionavimo aprašymą schematine struktūra apskaičiuoja sistemos stacionariąsias tikimybes ir tikimybines charakteristikas. / This paper analyses the underlying multi-server and multi-class queuing system which is receiving applications of corresponding intensities distributed by Poisson process and can be spread among multi-class servers with fixed waiting positions, where service time S of a application has a general probability distribution function G(t). The object of this paper is to create the software which enables to compute stationary probabilities and to estimate stochastic characteristics of the system which is defined in schematic structure.

Active Queue Management (AQM) aims to achieve high link utilization, low queuing delay and low loss rate in routers. However, it is difficult to adapt AQM parameters to constantly provide desirable transient and steady-state performance under highly dynamic network scenarios. They need to be a trade-off made between queuing delay and utilization. The queue size would become unstable when round-trip time or link capacity increases, or would be unnecessarily large when round-trip time or link capacity decreases. Effective ways of adapting AQM parameters to obtain good performance have remained a critical unsolved problem during the last fifteen years. This thesis firstly investigates existing AQM algorithms and their performance. Based on a previously developed dynamic model of TCP behaviour and a linear feedback model of TCP/RED, Auto-Parameterization RED (AP-RED) is proposed which unveils the mechanism of adapting RED parameters according to measurable network conditions. Another algorithm of Statistical Tuning RED (ST-RED) is developed for systematically tuning four key RED parameters to control the local stability in response to the detected change in the variance of the queue size. Under variable network scenarios like round-trip time, link capacity and traffic load, no manual parameter configuration is needed. The proposed ST-RED can adjust corresponding parameters rapidly to maintain stable performance and keep queuing delay as low as possible. Thus the sensitivity of RED's performance to different network scenarios is removed. This Statistical Tuning algorithm can be applied to a PI controller for AQM and a Statistical Tuning PI (ST-PI) controller is also developed. The implementation of ST-RED and ST-PI is relatively straightforward. Simulation results demonstrate the feasibility of ST-RED and ST-PI and their capabilities to provide desirable transient and steady-state performance under extensively varying network conditions.

Data fusion in wireless sensor networks can improve the performance of a network by eliminating redundancy and power consumption, ensuring fault-tolerance between sensors, and managing e®ectively the available com- munication bandwidth between network components. This thesis considers a data fusion approach applied to wireless sensor networks based on fuzzy logic theory. In particular, a cluster-based hierarchical design in wire- less sensor networks is explored combined with two data fusion methods based on fuzzy logic theory. A data fusion algorithm is presented and tested using Mamdani and Tsukamoto fuzzy inference methods. In addition, a concept related to the appropriate queuing models is presented based on classical queuing theory. Results show that the Mamdani method gives better results than the Tsukamoto approach for the two implementations considered. We noted that the proposed algorithm requires low processing and computational power. As a result, it can be applied to WSNs to provide optimal data fusion and ensures maximum sensor lifetime and minimum time delay.

Wireless networks are undergoing an unprecedented revolution in the last decade. With the explosion of delay-sensitive applications in the Internet (i.e., online gaming and VoIP), latency becomes a major issue for the development of wireless technology. Taking advantage of the significant decline in memory prices, industrialists equip the network devices with larger buffering capacities to improve the network throughput by limiting packets drops. Over-buffering results in increasing the time that packets spend in the queues and, thus, introducing more latency in networks. This phenomenon is known as “bufferbloat”. While throughput is the dominant performance metric, latency also has a huge impact on user experience not only for real-time applications but also for common applications like web browsing, which is sensitive to latencies in order of hundreds of milliseconds. Concerns have arisen about designing sophisticated queue management schemes to mitigate the effects of such phenomenon. My thesis research aims to solve bufferbloat problem in both traditional half-duplex and cutting-edge full-duplex wireless systems by reducing delay while maximizing wireless links utilization and fairness. Our work shed lights on buffer management algorithms behavior in wireless networks and their ability to reduce latency resulting from excessive queuing delays inside oversized static network buffers without a significant loss in other network metrics. First of all, we address the problem of buffer management in wireless full-duplex networks by using Wireless Queue Management (WQM), which is an active queue management technique for wireless networks. Our solution is based on Relay Full-Duplex MAC (RFD-MAC), an asynchronous media access control protocol designed for relay full-duplexing. Compared to the default case, our solution reduces the end-to-end delay by two orders of magnitude while achieving similar throughput in most of the cases. In the second part of this thesis, we propose a novel design called “LearnQueue” based on reinforcement learning that can effectively control the latency in wireless networks. LearnQueue adapts quickly and intelligently to changes in the wireless environment using a sophisticated reward structure. Testbed results prove that LearnQueue can guarantee low latency while preserving throughput.

L'objectif principal de cette thèse consiste à apporter une contribution méthodologique à la gestion de la sûreté et de coût de la sûreté aéroportuaire. Nous avons proposé un modèle logique du système de contrôle du flux des passagers au départ dans un aéroport. La finalité de ce modèle a permis de tester différents scénarios d'attaque du système, d'analyser le comportement du système dans ces conditions et d'en évaluer la perméabilité. Nous nous sommes ensuite intéressé à l'évaluation du système de contrôle des flux de passagers à l'embarquement au travers d'une approche probabiliste. Ceci conduit à la formulation de problèmes d'optimisation permettant d'améliorer les performances du système de contrôle. Afin d'obtenir la modélisation mathématique des flux de passagers au départ dans une aérogare, nous avons introduit les facteurs temps et espace par rapport au modèle précédent afin de le rendre plus proche de l'opérationnel. Enfin, nous nous sommes intéressés à l'optimisation des affectations des ressources matérielles et humaines destinées au contrôle du trafic de passagers. Le modèle spatio-temporel développé précédemment est mis à profit pour quantifier de façon dynamique, l'attribution des ressources matérielles et humaines au niveau de l'inspection filtrage et surtout d'améliorer la qualité de service. Beaucoup reste à faire dans ce domaine et le développement d'outils de modélisation, d'analyse et d'aide à la décision tels que ceux qui ont été esquissés dans ce mémoire semble s'imposer pour assurer l'optimisation de l'affectation des ressources de la sûreté aéroportuaire et ainsi garantir non seulement la qualité du service de contrôle mais aussi le niveau de coûts en résultant. / Since the tragic events of September 11, aviation security is jeopardized. Many measures were taken both from the standpoint of improved procedures for improving the performance of security officers and equipment safety. Despite the implementation of new procedures and new measures, many events have shaken the airport security system established by ICAO, these include, the latest of which is the attempt acts of unlawful interference in December 2009. The main objective of this thesis is to contribute to methodological constraints security management and cost of airport security. To fight effectively against illegal acts, the standard 4.4.1 of Schedule 17 to the Chicago Convention states: “Each Contracting State shall establish measures to ensure that passengers from flights of commercial air transport and their cabin baggage are subjected to screened before boarding an aircraft departing from an area of security restricted”. The security check is then one of the highlights of airport security. We therefore propose a model system logic to control the flow of departing passengers at an airport. The purpose of this model was used to test different scenarios of attack system, analyze system behavior under these conditions and to assess permeability. We are then interested in evaluating the system of controlling the flow of passengers boarding through a probabilistic approach. This then leads to the formulation of optimization problems to improve the performance of the control system. It is then possible to establish operational procedures leading to improved system performance of passenger screening. To obtain the mathematical modeling of flow of departing passengers in a terminal, we introduced the factors of time and space relative to the previous model to make it closer to the operational. In this model, which adopts a network structure to describe the process and the transfer of passengers between the terminal sites, in particular allows to represent queues and waiting times inflicted on passengers. Finally, we are interested in optimizing the allocation of human and material resources for the control of passenger traffic. The spatio-temporal model developed previously is used to quantify dynamically allocating human and material resources at the security check and especially to improve the quality of service. This optimization allows us to formulate effective policies to manage the short term. Finally, modeling the performance of safety was performed according to a probabilistic point of view and then a dynamic perspective and space. In both cases the optimization problems were formulated based on the determination of operational parameters to improve system performance. Much remains to be done in this area and the development of tools for modeling, analysis and decision support such as those outlined in this paper seems to be necessary to ensure optimal allocation resources for airport security and so ensure not only quality service but also control the level of the resulting costs.

Effective aeromedical evacuation of casualties is one of the most important problems in military medical systems because high-priority casualties will not survive without timely medical care. The decision making process for aeromedical evacuation consists of the following components: (1) identifying which aeromedical evacuation asset (see figure 1) to dispatch to the casualty, (2) locating aeromedical evacuation assets strategically in anticipation of incoming demand, and (3) deciding which medical treatment facility to transport the casualty. These decisions are further complicated because prioritization of casualties is based on severity of injury while aeromedical evacuation assets and medical treatment facilities operate with varying capabilities. In this dissertation, discrete optimization models are developed to examine dispatch, delivery, and location logistics for the effective aeromedical evacuation of casualties in military medical systems.

Este trabalho apresenta uma proposta de Arquitetura Orientada a Serviço para desenvolvimento de aplicações com restrições temporais, isto é, aplicações em que o tempo de resposta a uma requisição deve respeitar limites máximos. No desenvolvimento da arquitetura proposta foram considerados os modelos de filas com um único servidor e com múltiplos servidores, por meio da utilização de serviços redundantes e do escalonamento de requisições para melhoria do determinismo no tempo de resposta das requisições efetuadas. Para avaliação da arquitetura proposta foi construído um sistema de testes de forma a ser observado o comportamento do tempo de resposta das requisições em função do número de servidores disponíveis e sua respectiva taxa de utilização. Os resultados obtidos indicam que é possível obter um aumento no determinismo do tempo de resposta das requisições efetuadas (diminuição da dispersão de valores), tendo sido obtidos resultados semelhantes para os dois algoritmos de escalonamento utilizados: por ordem de chegada das requisições e SRPT (Shortest Remaining Processing Time). / This thesis presents a proposal for a Service Oriented Architecture applied to development of time constrained systems, where the timeliness of the results is a major requirement. The development is based on the queuing theory (models using one and multiple servers) and requests scheduling to improve response time determinism. In order to verify the proposal, a test system had been developed to observe the dynamic behavior of the requests response time dispersion according to the number of servers available and associated processing rate. The results obtained show an improvement over the request response time determinism and almost similar performance for the two scheduling algorithms used: request arrival order and SRPT (Shortest Remaining Processing Time).