О применении грациозной разметки в MPLS-сетях

Рассмотрены графовые модели на основе грациозных разметок, используемых при решении оптимизационных задач в современных сетях передачи данных.Мета статті. Провести дослідження, яке рередбачає розробку ефективного способу пересилання пакетів, що сприяє поліпшенню показників часу життя пакета і підвищенню надійності роботи мережі. Методи. На основі повної топологічної карти мережі, що моделюється графом G=(V, E), обчислюється кістякове дерево мінімальної ваги. Для цього може бути застосований протокол OSPF, який визначає маршрут найменшої вартості в заданій метриці – мінімальна затримка. Далі активізується алгоритм граціозної розмітки, що призначає маршрутизаторам мітки, які в свою чергу породжують мітки каналів зв’язку. Приєднання або видалення учасників групи при багатоадресній маршрутизації реалізовано за використання алгоритму перенумерації вершин граціозної гусениці. Результат. Розроблено ефективний спосіб транспортування пакетів, що сприяє поліпшенню показників часу життя пакета і підвищенню надійності роботи мережі.Purpose. To conduct studies to optimize the process of traffic transmission over the network with MPLS functions. Methods. Based on the complete topological map of the network, modeled by the graph G=(V, E), a spanning tree of minimum weight is calculated. For this purpose, the OSPF protocol can be applied, which determines the route of the lowest cost in the given metric – the minimum delay. Next comes the graceful labelling algorithm, which assigns tags to the routers, which in their turn generate the labels of the communication channels. Joining or deleting members of a group with multicast routing is implemented using the algorithm of renumbering vertices of a graceful caterpillar. Results. Development of an effective packet forwarding method that would improve the packet lifetime parameters and increase the reliability of the network operation

Застосування регресійної моделі коефіцієнта використання каналів для формування плану розподілу навантаження в мережі

Introduction. Method of problem solutions of management, design and quality evaluation using mathematical models coefficient utilization of channels (CUC) in standard form has several inconveniences. It is connected with fact models used analytical expressions that are not derivatives and don’t explicitly get some parameters dependence by others. Formulation of the problem. Objective is obtain approximate analytical coefficient dependence channel utilization ratio of the load, the number of channels and allowable probability of loss requests on branches network. This ratio reflects essence of processes occurring in network with a high level of adequacy and differentiated range of values explored. Solution. The problem definition of empirical relationships is conducted by two stages. At the first stage the general form of analytical expressions was determined (7). In the second stage best settings analytical expressions were calculated. The calculation results are represented in Tables 1 and 2. Analysis of the CUC is carried by the first derivative functions. Results. Analytical dependences of the CCC were obtained. They allow you to remove indeterminacy in the solution of nonlinear equations. This nonlinear system describes the requirements for quality of service in connection direction. This reduces the requested channel resource in the network. That allows providing a certain quality of service in connection direction.При решении задач управления, проектирования и оценки качества обслуживания в телекоммуникационных сетях нередко используется математическая модель коэффициента использования каналов. Однако, ее использование в стандартном виде имеет ряд неудобств. Это связано с тем, что используемые в модели аналитические выражения не дифференцируемы и не позволяют в явном виде выражать зависимость одних параметров через другие. В статье предложена аппроксимация математической модели коэффициента использования каналов приближенными дифференцируемыми функциями на базе математического аппарата регрессионного анализа. Даны рекомендации по использованию полученных результатов в ходе решения сетевых задач.При вирішенні завдань управління, проектування і оцінки якості обслуговування в телекомунікаційних мережах нерідко використовується математична модель коефіцієнта використання каналів. Однак, її використання в стандартному вигляді має ряд незручностей. Це пов'язано з тим, що в моделі використовуються аналітичні вирази, які не мають похідні і не дозволяють в явному вигляді отримувати залежність одних параметрів через інші. У статті запропонована апроксимація математичної моделі коефіцієнта використання каналів наближеними диференційованими функціями на базі математичного апарату регресійного аналізу. Надано рекомендації щодо використання отриманих результатів в ході вирішення мережевих задач

Optimizing the investments in mobile networks and subscriber migrations for a telecommunication operator

We consider the context of a telecommunications company that is at the same time an infrastructure operator and a service provider. When planning its network expansion, the company can leverage over its knowledge of subscribers dynamic to better optimize the network dimensioning, therefore avoiding unnecessary costs. In this work, the network expansion represents the deployment and/or reinforcement of several technologies (e.g. 2G,3G,4G), assuming that subscribers to a given technology can be served by this technology or older ones. The operator can influence subscribers dynamic by subsidies. The planning is made over a discretized time horizon while some strategic guidelines requirements are demanded at the end of the time horizon. Following classical models, we consider that the behavior of customers follows an S-shape piecewise constant function. We propose a Mixed-Integer Linear Programming formulation and a heuristic algorithm for the multi-year planning problem. The scalability of the formulation and the quality of the heuristic are assessed numerically on real instances for a use-case with two generations

The Multilayer Capacitated Survivable IP Network Design Problem : valid inequalities and Branch-and-Cut

Telecommunication networks can be seen as the stacking of several layers like, for instance, IP-over-Optical networks. This infrastructure has to be sufficiently survivable to restore the traffic in the event of a failure. Moreover, it should have adequate capacities so that the demands can be routed between the origin-destinations. In this paper we consider the Multilayer Capacitated Survivable IP Network Design problem. We study two variants of this problem with simple and multiple capacities. We give two multicommodity flow formulations for each variant of this problem and describe some valid inequalities. In particular, we characterize valid inequalities obtained using Chvatal-Gomory procedure from the well known Cutset inequalities. We show that some of these inequalities are facet defining. We discuss separation routines for all the valid inequalities. Using these results, we develop a Branch-and-Cut algorithm and a Branch-and-Cut-and-Price algorithm for each variant and present extensive computational results

OR for entrepreneurial ecosystems : a problem-oriented review and agenda

Innovation-driven entrepreneurship has become a focus for economic development and received increasing attention from policy makers and academics over the last decades. While consensus has been reached that context matters for innovation and entrepreneurship, little evidence and decision support exists for policy makers to effectively shape the environment for growth-oriented companies. We present the entrepreneurial ecosystem concept as a complex systems-based approach to the study of innovation-driven entrepreneurial economies. The concept, in combination with novel data sources, offers new opportunities for research and policy, but also comes with new challenges. The aim of this paper is to take stock of the literature and build bridges for more transdisciplinary research. First, we review emergent trends in ecosystem research and provide a typology of four overarching problems based on current limitations. These problems connect operational research scholars to the context and represent focal points for their contributions. Second, we review the operational research literature and provide an overview of how these problems have been addressed and outline opportunities for future research, both for the specific problems as well as cross-cutting themes. Operational research has been invaluable in supporting decision-makers facing complex problems in several fields. This paper provides a conceptual and methodological agenda to increase its contribution to the study and governance of entrepreneurial ecosystems

Characterization, design and re-optimization on multi-layer optical networks

L'augment de volum de tràfic IP provocat per l'increment de serveis multimèdia com HDTV o vídeo conferència planteja nous reptes als operadors de xarxa per tal de proveir transmissió de dades eficient. Tot i que les xarxes mallades amb multiplexació per divisió de longitud d'ona (DWDM) suporten connexions òptiques de gran velocitat, aquestes xarxes manquen de flexibilitat per suportar tràfic d’inferior granularitat, fet que provoca un pobre ús d'ample de banda. Per fer front al transport d'aquest tràfic heterogeni, les xarxes multicapa representen la millor solució. Les xarxes òptiques multicapa permeten optimitzar la capacitat mitjançant l'empaquetament de connexions de baixa velocitat dins de connexions òptiques de gran velocitat. Durant aquesta operació, es crea i modifica constantment una topologia virtual dinàmica gràcies al pla de control responsable d’aquestes operacions. Donada aquesta dinamicitat, un ús sub-òptim de recursos pot existir a la xarxa en un moment donat. En aquest context, una re-optimizació periòdica dels recursos utilitzats pot ser aplicada, millorant així l'ús de recursos. Aquesta tesi està dedicada a la caracterització, planificació, i re-optimització de xarxes òptiques multicapa de nova generació des d’un punt de vista unificat incloent optimització als nivells de capa física, capa òptica, capa virtual i pla de control. Concretament s'han desenvolupat models estadístics i de programació matemàtica i meta-heurístiques. Aquest objectiu principal s'ha assolit mitjançant cinc objectius concrets cobrint diversos temes oberts de recerca. En primer lloc, proposem una metodologia estadística per millorar el càlcul del factor Q en problemes d'assignació de ruta i longitud d'ona considerant interaccions físiques (IA-RWA). Amb aquest objectiu, proposem dos models estadístics per computar l'efecte XPM (el coll d'ampolla en termes de computació i complexitat) per problemes IA-RWA, demostrant la precisió d’ambdós models en el càlcul del factor Q en escenaris reals de tràfic. En segon lloc i fixant-nos a la capa òptica, presentem un nou particionament del conjunt de longituds d'ona que permet maximitzar, respecte el cas habitual, la quantitat de tràfic extra proveït en entorns de protecció compartida. Concretament, definim diversos models estadístics per estimar la quantitat de tràfic donat un grau de servei objectiu, i diferents models de planificació de xarxa amb l'objectiu de maximitzar els ingressos previstos i el valor actual net de la xarxa. Després de resoldre aquests problemes per xarxes reals, concloem que la nostra proposta maximitza ambdós objectius. En tercer lloc, afrontem el disseny de xarxes multicapa robustes davant de fallida simple a la capa IP/MPLS i als enllaços de fibra. Per resoldre aquest problema eficientment, proposem un enfocament basat en sobre-dimensionar l'equipament de la capa IP/MPLS i recuperar la connectivitat i el comparem amb la solució convencional basada en duplicar la capa IP/MPLS. Després de comparar solucions mitjançant models ILP i heurístiques, concloem que la nostra solució permet obtenir un estalvi significatiu en termes de costos de desplegament. Com a quart objectiu, introduïm un mecanisme adaptatiu per reduir l'ús de ports opto-electrònics (O/E) en xarxes multicapa sota escenaris de tràfic dinàmic. Una formulació ILP i diverses heurístiques són desenvolupades per resoldre aquest problema, que permet reduir significativament l’ús de ports O/E en temps molt curts. Finalment, adrecem el problema de disseny resilient del pla de control GMPLS. Després de proposar un nou model analític per quantificar la resiliència en topologies mallades de pla de control, usem aquest model per proposar un problema de disseny de pla de control. Proposem un procediment iteratiu lineal i una heurística i els usem per resoldre instàncies reals, arribant a la conclusió que es pot reduir significativament la quantitat d'enllaços del pla de control sense afectar la qualitat de servei a la xarxa.The explosion of IP traffic due to the increase of IP-based multimedia services such as HDTV or video conferencing poses new challenges to network operators to provide a cost-effective data transmission. Although Dense Wavelength Division Multiplexing (DWDM) meshed transport networks support high-speed optical connections, these networks lack the flexibility to support sub-wavelength traffic leading to poor bandwidth usage. To cope with the transport of that huge and heterogeneous amount of traffic, multilayer networks represent the most accepted architectural solution. Multilayer optical networks allow optimizing network capacity by means of packing several low-speed traffic streams into higher-speed optical connections (lightpaths). During this operation, a dynamic virtual topology is created and modified the whole time thanks to a control plane responsible for the establishment, maintenance, and release of connections. Because of this dynamicity, a suboptimal allocation of resources may exist at any time. In this context, a periodically resource reallocation could be deployed in the network, thus improving network resource utilization. This thesis is devoted to the characterization, planning, and re-optimization of next-generation multilayer networks from an integral perspective including physical layer, optical layer, virtual layer, and control plane optimization. To this aim, statistical models, mathematical programming models and meta-heuristics are developed. More specifically, this main objective has been attained by developing five goals covering different open issues. First, we provide a statistical methodology to improve the computation of the Q-factor for impairment-aware routing and wavelength assignment problems (IA-RWA). To this aim we propose two statistical models to compute the Cross-Phase Modulation variance (which represents the bottleneck in terms of computation time and complexity) in off-line and on-line IA-RWA problems, proving the accuracy of both models when computing Q-factor values in real traffic scenarios. Second and moving to the optical layer, we present a new wavelength partitioning scheme that allows maximizing the amount of extra traffic provided in shared path protected environments compared with current solutions. Specifically, we define several statistical models to estimate the traffic intensity given a target grade of service, and different network planning problems for maximizing the expected revenues and net present value. After solving these problems for real networks, we conclude that our proposed scheme maximizes both revenues and NPV. Third, we tackle the design of survivable multilayer networks against single failures at the IP/MPLS layer and WSON links. To efficiently solve this problem, we propose a new approach based on over-dimensioning IP/MPLS devices and lightpath connectivity and recovery and we compare it against the conventional solution based on duplicating backbone IP/MPLS nodes. After evaluating both approaches by means of ILP models and heuristic algorithms, we conclude that our proposed approach leads to significant CAPEX savings. Fourth, we introduce an adaptive mechanism to reduce the usage of opto-electronic (O/E) ports of IP/MPLS-over-WSON multilayer networks in dynamic scenarios. A ILP formulation and several heuristics are developed to solve this problem, which allows significantly reducing the usage of O/E ports in very short running times. Finally, we address the design of resilient control plane topologies in GMPLS-enabled transport networks. After proposing a novel analytical model to quantify the resilience in mesh control plane topologies, we use this model to propose a problem to design the control plane topology. An iterative model and a heuristic are proposed and used to solve real instances, concluding that a significant reduction in the number of control plane links can be performed without affecting the quality of service of the network

B.: The multi-layered network design problem

Abstract We address the problem of designing a network built on several layers. This problem occurs in practical applications but has not been studied extensively from the point of view of global optimisation, since the problem of designing a singlelayered network is complex. An example of an application is the design of a virtual network (Internet Protocol) built on a sparse optical transport network. We suggest a mathematical formulation without any flow variables or path variables, based on metric inequalities. We give numerical results for two-layered network instances obtained with a global method giving optimal solutions and we compare them with approximate results obtained by solving the problem in two steps