MILP-based heuristics for the design of rural community electrification projects

Wind-photovoltaic systems are a suitable option to provide electricity to isolated communities autonomously. To design these systems, there are recent mathematical models that solve the location and type of each of the electrification components and the design of the possible distribution microgrids. When the amount of demand points to electrify increases, solving the mathematical model requires a computational time that becomes infeasible in practice. To speed up the solving process, three heuristic methods based on mixed integer linear programming (MILP) are presented in this paper: Relax and Fix heuristics, heuristics based on a Corridor Method and Increasing Radius heuristics. In all algorithms first a relaxed MILP is solved to obtain a base solution and then it is used as a starting point to find a feasible solution by searching in a reduced search space. For each type of heuristic several options to relax and to reduce the solution space are developed and tested. Extensive computational experiments based on real projects are carried out and results show that the best heuristic vary according to the size of instances.Postprint (author's final draft

Message routing between the As/400 token ring network and the Internet

A working model of the message exchange system is designed and developed for the AS/400 systems, a type of mid-range computer developed by IBM, thus enabling the Message Routing between the AS/400 Token Ring Network and the Internet. The routing system accommodates the in-built messaging function in the midrange computer, hence providing a common familiar interface to the user. The message system typically includes a router and an intermediate host system connected to a computer which provides the access to the Internet (technically referred as Internet Gateway). The router becomes the bridging unit between the Internet and the midrange host. The router uses two different protocols to communicate with the midrange host and the Internet. However the message exchanges are never affected by these differences in the protocol, since they are accomplished at a higher level of communication

Characterizing capital and operational tradeoffs resulting from fiber-to-the-home optical network architecture choice

Thesis (S.M.)--Massachusetts Institute of Technology, Engineering Systems Division; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 127-128).This thesis explores the impact of relative lifecycle cost tradeoffs on technology strategy, and characterizes two factors driving these costs: population demographics, and uncertainty in component costs. The methodology developed consists of three novel components which address gaps in the current literature in the areas of large-scale network design, multi-attribute population characterization, and cost modeling. Three technologies representing near, mid, and long-term fiber-to-the-home gigabit passive optical network solutions, and seven implementation strategies are dimensioned for two significantly different population demographics, each representing large coverage regions containing millions of subscribers. The methodology is able to successfully characterize how relative network topologies changed as a function of population attributes, revealing complex cost tradeoffs between technology strategies.by Thomas Rand-Nash.S.M

Design of Overlay Networks for Internet Multicast - Doctoral Dissertation, August 2002

Multicast is an efficient transmission scheme for supporting group communication in networks. Contrasted with unicast, where multiple point-to-point connections must be used to support communications among a group of users, multicast is more efficient because each data packet is replicated in the network – at the branching points leading to distinguished destinations, thus reducing the transmission load on the data sources and traffic load on the network links. To implement multicast, networks need to incorporate new routing and forwarding mechanisms in addition to the existing are not adequately supported in the current networks. The IP multicast are not adequately supported in the current networks. The IP multicast solution has serious scaling and deployment limitations, and cannot be easily extended to provide more enhanced data services. Furthermore, and perhaps most importantly, IP multicast has ignored the economic nature of the problem, lacking incentives for service providers to deploy the service in wide area networks. Overlay multicast holds promise for the realization of large scale Internet multicast services. An overlay network is a virtual topology constructed on top of the Internet infrastructure. The concept of overlay networks enables multicast to be deployed as a service network rather than a network primitive mechanism, allowing deployment over heterogeneous networks without the need of universal network support. This dissertation addresses the network design aspects of overlay networks to provide scalable multicast services in the Internet. The resources and the network cost in the context of overlay networks are different from that in conventional networks, presenting new challenges and new problems to solve. Our design goal are the maximization of network utility and improved service quality. As the overall network design problem is extremely complex, we divide the problem into three components: the efficient management of session traffic (multicast routing), the provisioning of overlay network resources (bandwidth dimensioning) and overlay topology optimization (service placement). The combined solution provides a comprehensive procedure for planning and managing an overlay multicast network. We also consider a complementary form of overlay multicast called application-level multicast (ALMI). ALMI allows end systems to directly create an overlay multicast session among themselves. This gives applications the flexibility to communicate without relying on service provides. The tradeoff is that users do not have direct control on the topology and data paths taken by the session flows and will typically get lower quality of service due to the best effort nature of the Internet environment. ALMI is therefore suitable for sessions of small size or sessions where all members are well connected to the network. Furthermore, the ALMI framework allows us to experiment with application specific components such as data reliability, in order to identify a useful set of communication semantic for enhanced data services

Circuit design and analysis for on-FPGA communication systems

On-chip communication system has emerged as a prominently important subject in Very-Large- Scale-Integration (VLSI) design, as the trend of technology scaling favours logics more than interconnects. Interconnects often dictates the system performance, and, therefore, research for new methodologies and system architectures that deliver high-performance communication services across the chip is mandatory. The interconnect challenge is exacerbated in Field-Programmable Gate Array (FPGA), as a type of ASIC where the hardware can be programmed post-fabrication. Communication across an FPGA will be deteriorating as a result of interconnect scaling. The programmable fabrics, switches and the specific routing architecture also introduce additional latency and bandwidth degradation further hindering intra-chip communication performance. Past research efforts mainly focused on optimizing logic elements and functional units in FPGAs. Communication with programmable interconnect received little attention and is inadequately understood. This thesis is among the first to research on-chip communication systems that are built on top of programmable fabrics and proposes methodologies to maximize the interconnect throughput performance. There are three major contributions in this thesis: (i) an analysis of on-chip interconnect fringing, which degrades the bandwidth of communication channels due to routing congestions in reconfigurable architectures; (ii) a new analogue wave signalling scheme that significantly improves the interconnect throughput by exploiting the fundamental electrical characteristics of the reconfigurable interconnect structures. This new scheme can potentially mitigate the interconnect scaling challenges. (iii) a novel Dynamic Programming (DP)-network to provide adaptive routing in network-on-chip (NoC) systems. The DP-network architecture performs runtime optimization for route planning and dynamic routing which, effectively utilizes the in-silicon bandwidth. This thesis explores a new horizon in reconfigurable system design, in which new methodologies and concepts are proposed to enhance the on-FPGA communication throughput performance that is of vital importance in new technology processes

Context-based security function orchestration for the network edge

Over the last few years the number of interconnected devices has increased dramatically, generating zettabytes of traffic each year. In order to cater to the requirements of end-users, operators have deployed network services to enhance their infrastructure. Nowadays, telecommunications service providers are making use of virtualised, flexible, and cost-effective network-wide services, under what is known as Network Function Virtualisation (NFV). Future network and application requirements necessitate services to be delivered at the edge of the network, in close proximity to end-users, which has the potential to reduce end-to-end latency and minimise the utilisation of the core infrastructure while providing flexible allocation of resources. One class of functionality that NFV facilitates is the rapid deployment of network security services. However, the urgency for assuring connectivity to an ever increasing number of devices as well as their resource-constrained nature, has led to neglecting security principles and best practices. These low-cost devices are often exploited for malicious purposes in targeting the network infrastructure, with recent volumetric Distributed Denial of Service (DDoS) attacks often surpassing 1 terabyte per second of network traffic. The work presented in this thesis aims to identify the unique requirements of security modules implemented as Virtual Network Functions (VNFs), and the associated challenges in providing management and orchestration of complex chains consisting of multiple VNFs The work presented here focuses on deployment, placement, and lifecycle management of microservice-based security VNFs in resource-constrained environments using contextual information on device behaviour. Furthermore, the thesis presents a formulation of the latency-optimal placement of service chains at the network edge, provides an optimal solution using Integer Linear Programming, and an associated near-optimal heuristic solution that is able to solve larger-size problems in reduced time, which can be used in conjunction with context-based security paradigms. The results of this work demonstrate that lightweight security VNFs can be tailored for, and hosted on, a variety of devices, including commodity resource-constrained systems found in edge networks. Furthermore, using a context-based implementation of the management and orchestration of lightweight services enables the deployment of real-world complex security service chains tailored towards the user’s performance demands from the network. Finally, the results of this work show that on-path placement of service chains reduces the end-to-end latency and minimise the number of service-level agreement violations, therefore enabling secure use of latency-critical networks

Procediments heurístics de disseny de sistemes d'electrificació rural amb energies renovables

Electrification hybrid systems (wind-photovoltaic systems) are a suitable option to supply electricity independently in isolated communities. To design these systems, there are recent mathematical models that provide the location and type of each of the electrification components and the design of the possible micro-distribution networks. When the amount of consumption points to electrify increases, solving the mathematical models require computational times that become infeasible in practice. For these cases, three heuristic methods based on mixed integer linear programming (MILP) are presented in this thesis: Relax and Fix heuristics, heuristics based on Corridor Method and Increasing Radius heuristics. In all procedures first a relaxed MILP is solved to obtain a base solution and then it is used as a starting point to find a feasible solution by searching in a more reduced search space. For each type of heuristics several options to relax and to reduce the solution space were developed and tested. Finally, extensive computational experiments based on real projects were carried out and results show that the best heuristic to apply varies according to the size of the instances to be solved.Els sistemes d’electrificació híbrids (fotovoltaics i eòlics) són una opció adequada per a subministrar electricitat de forma autònoma a comunitats aïllades. Per a dissenyar aquests sistemes hi ha models matemàtics recents que proporcionen la ubicació i el tipus de cadascun dels components d'electrificació i també el disseny de les possibles micro-xarxes de distribució. Quan la quantitat de punts de consum per electrificar augmenta, les solucions dels models matemàtics requereixen uns temps de càlcul que en la pràctica es converteixen en inviables. Per aquests casos, en aquesta tesi es presenten tres procediments heurístics basats en programació lineal entera mixta (PLEM): heurístiques de Relaxament i Fixació, heurístiques basades en el Corridor Method i les heurístiques aquí anomenades de Radis creixents. En tots els procediments primer es resol un model PLEM relaxat per tal d’obtenir una solució base que després s'utilitza com a punt de partida per trobar una solució factible mitjançant la recerca en un espai de cerca més reduït. S’han desenvolupat i provat diverses opcions de relaxament i de reducció de l'espai de cerca per a cada tipus d’heurística. Finalment, s’han dut a terme extensos experiments computacionals basats en projectes reals i els resultats mostren que la millor heurística a aplicar varia segons la mida dels exemplars a resoldre.Los sistemas de electrificación híbridos (fotovoltaicos y eólicos) son una opción adecuada para suministrar electricidad de forma autónoma a comunidades aisladas. Para diseñar estos sistemas hay modelos matemáticos recientes que proporcionan la ubicación y el tipo de cada uno de los componentes de electrificación y también el diseño de las posibles micro-redes de distribución. Cuando la cantidad de puntos de consumo para electrificar aumenta, las soluciones de los modelos matemáticos requieren tiempos de cálculo que en la práctica se convierten en inviables. Para estos casos, en esta tesis se presentan tres procedimientos heurísticos basados en programación lineal entera mixta (PLEM): heurísticas de Relajación y Fijación, heurísticas basadas en el Corridor Method y las heurísticas aquí llamadas de Radios crecientes. En todos los procedimientos primero se resuelve un modelo PLEM relajado para obtener una solución base que luego se utiliza como punto de partida para encontrar una solución factible mediante la búsqueda en un espacio de búsqueda más reducido. Se han desarrollado y probado varias opciones de relajación y de reducción del espacio de búsqueda para cada tipo de heurística. Finalmente, se han llevado a cabo extensos experimentos computacionales basados en proyectos reales y los resultados muestran que la mejor heurística a aplicar varía según el tamaño de los ejemplares a resolverPostprint (published version