Efficient calculation of the most reliable pair of link disjoint paths in telecommunication networks

In transmission networks an important routing problem is to find a pair of link disjoint paths which optimises some performance measure. In this paper the problem of obtaining the most reliable pair of link disjoint paths, assuming the reliability of the links are known, is considered. This is a non-linear optimisation problem. It is further introduced the constraint that the length of the paths should not exceed a certain number of links, which makes the efficient resolution of the problem more complex.http://www.sciencedirect.com/science/article/B6VCT-4JS20BJ-2/1/d3a0679a9c65e51ae2074080f957df9

An effective algorithm for obtaining the whole set of minimal cost pairs of disjoint paths with dual arc costs

In telecommunication networks design the problem of obtaining optimal (arc or node) disjoint paths, for increasing network reliability, is extremely important. The problem of calculating kc disjoint paths from s to t (two distinct nodes), in a network with kc different (arbitrary) costs on every arc such that the total cost of the paths is minimised, is NP-complete even for kc = 2. When kc = 2 these networks are usually designated as dual arc cost networks. In this paper we propose an exact algorithm for finding the whole set of arc-disjoint path pairs, with minimal cost in a network with dual arc costs. The correctness of the algorithm is based on a condition which guarantees that the optimal path pair cost has been obtained and on a proposition which guarantees that at the end of the algorithm all the optimal pairs have been obtained. The optimality condition is based on the calculation of upper and lower bounds on the optimal cost. Extensive experimentation is presented to show the effectiveness of the algorithm

On a Bicriterion Server Allocation Problem for a Multidimensional Erlang Loss System

In this work an optimization problem on a classical elementary stochastic system system, modeled as an Erlang-B (M/M/x) loss system, is formulated by using a bicriteria approach. The problem is focused on the allocation of a given total of k servers to a number of groups of servers capable of carrying certain offered traffic processes assumed as Poissonian in nature. Two main objectives are present in this formulation. Firstly a criterion of equity in the grade of service, measured by the call blocking probabilities, entails that the absolute difference between the blocking probabilities experienced by the calls in the different service groups must be as small as possible. Secondly a criterion of system economic performance optimization requires the total traffic carried by the system, to be maximized. Relevant mathematical results characterizing the two objective functions and the set N of the non-dominated solutions, are presented. An algorithm for traveling on N based on the resolution of single criterion convex problems, using a Newton-Raphson method, is also proposed. In each iteration the two first derivatives of the Erlang-B function in the number of circuits (a difficult numerical problem) are calculated using a method earlier proposed. Some computational results are also presented

Network performance of multi-service circuit switched networks simulational comparison of variants of DAR and RTNR

The use of dynamic routing methods has an important impact on the performance of multi-service networks namely in overload and failure conditions. The paper describes and compares the performance of variants of reference dynamic routing methods (DAR and RTNR). Two variants of DAR resulting from the extension to multi-service networks of the original formulation of the method are presented. Also a simplification of the trunk reservation mechanism per traffic class of RTNR is considered. The major results of extensive experimentation with these variants of the routing methods using a discrete event simulation platform are discussed. The simulation model includes Poisson and Engset type multi-class traffic flows. Conclusions concerning the relative performance of the methods at network level and per traffic class are put forward.Work partially supported by programme POSI of the IIIrd EU programme co-sponsored by FEDER and national funds.info:eu-repo/semantics/publishedVersio

Constructing minimal cost/minimal SRLG spanning trees Over optical networks - An exact approach

The construction of overlay or broadcast networks, based on spanning trees, over WDM optical networks with SRLG information has important applications in telecommunications. In this paper we propose a bicriteria optimisation model for calculating communication spanning trees over WDM networks the objectives of which are the minimisation of the total number of different SRLGs of the tree links (seeking to maximise reliability) and the minimisation of the total bandwidth usage cost. An exact algorithm for generating the whole set of non-dominated solutions and methods for selecting a final solution in various decision environments, are put forward. An extensive experimental study on the application of the model, including two sets of experiments based on reference transport network topologies, with random link bandwidth occupations and with random SRLG assignments to the links, is also presented, together with a discussion on potential advantages of the model

Determinação de k caminhos disjuntos nos SRLG

A determinação de um conjunto de caminhos disjuntos nos SRLG é um problema NP-Completo, de grande interesse no desenvolvimento de métodos de encaminhamento resiliente. Existem poucas heurísticas para a determinação de k de caminhos disjuntos nos SRLG, e tanto quanto nos foi possível averiguar, não existe nenhuma heurística que tente minimizar o custo total do conjunto de caminhos a determinar. São aqui propostas duas heurísticas que procuram determinar um conjunto de k caminhos disjuntos nos nós e nos SRLG, de custo aditivo mínimo.partially supported by FCT under project grant PEst-C/EEI/UI0308/2011, by programme COMPETE of the EC Community Support Framework III and cosponsored by the EC fund FEDER and national funds (FCT - PTDC/EEA-TEL/101884/2008) and PT Inovação by Project \Proteção extremo-a-extremo em redes GMPLS, considerando informação acerca de SRLG

Two heuristics for calculating a shared risk link group disjoint set of paths of min-sum cost

A shared risk link group (SRLG) is a set of links which share a common risk of failure. Routing protocols in Generalized MultiProtocol Label Switching, using distributed SRLG information, can calculate paths avoiding certain SRLGs. For single SRLG failure an end-to-end SRLG-disjoint path pair can be calculated, but to ensure connection in the event of multiple SRLG failures a set with more than two end-to-end SRLG-disjoint paths should be used. Two heuristic, the Conflicting SRLG-Exclusion Min Sum (CoSE-MS) and the Iterative Modified Suurballes’s Heuristic (IMSH), for calculating node and SRLG-disjoint path pairs, which use the Modified Suurballes’s Heuristic, are reviewed and new versions (CoSE-MScd and IMSHd) are proposed, which may improve the number of obtained optimal solutions. Moreover two new heuristics are proposed: kCoSE-MScd and kIMSHd, to calculate a set of k node and SRLG-disjoint paths, seeking to minimize its total cost. To the best of our knowledge these heuristics are a first proposal for seeking a set of k ðk[2Þ node and SRLG-disjoint paths of minimal additive cost. The performance of the proposed heuristics is evaluated using a real network structure, where SRLGs were randomly defined. The number of solutions found, the percentage of optimal solutions and the relative error of the sub-optimal solutions are presented. Also the CPU time for solving the problem in a path computation element is reported

Hierarchical Multiobjective Routing Model in MPLS Networks with Two Service Classes – A Comparison Case Study, Journal of Telecommunications and Information Technology, 2012, nr 2

A two-level hierarchical multicriteria routing model for multiprotocol label switching networks with two service classes (QoS, i.e., with quality of service requirements, and best effort services) and alternative routing is reviewed in this paper. A heuristic resolution approach, where nondominated solutions are obtained throughout the heuristic run and kept in an archive for further analysis is also reviewed. In this paper, an extensive analysis of the application of this procedure to two reference test networks for various traffic matrices is presented. Also a comparison of the results of our method with a lexicographic optimization approach based on a multicommodity flow formulation using virtual networks is carried out. Finally, results of a stochastic discrete event simulation model developed for these networks will be shown to illustrate the effectiveness of the resolution approach and to assess the inaccuracies of the analytic results

Edição Casa dos Estudantes do Império - Lisboa

A Casa dos Estudantes do Império (CEI) foi criada em 1944, pelo regime anterior, para responder ao reforço do convívio dos estudantes universitários das ex-colónias portuguesas, que não possuíam instituições de ensino superior e que tinham assim que continuar a frequência universitária em Portugal. Este objetivo integrou-se num outro, mais visto, de formação de eleitos que se admitiam virem a ser enquadradoras dos objetivos que o próprio regime colonial prosseguia. Sob os ventos da descolonização, documentos da Segunda Guerra Mundial, e da aprovação da Carta das Nações Unidas que reconhecem o direito inalienável dos povos à autodeterminação e à independência, o mundo assistiu ao surgimento de novos países no continente africano, o primeiro dos quais foi o Gana, em 1957. A partir dessa altura muitos dos associados da Casa dos Estudantes do Império são impulsionados para o aprofundamento dos estudos relativos à identidade dos territórios de que eram originários, frequentando debates, colóquios e promovendo edições próprias, com conteúdo diversificado, incluindo poemas, contos e outras formas de expressão cultural. Em resultado desta ação, a Casa dos Estudantes do Império é encerrada por intervenção da PIDE em 1965. Em 2015 ocorrerá a passagem do 50.º aniversário desse encerramento que coincide com o 40.º aniversário das independências das ex-colónias portuguesas. Foram associados da Casa dos Estudantes do Império, ou tiveram participação nela, personalidades incontornáveis da cultura e da política como Agostinho Neto, Amílcar Cabral, Lúcio Lara, Fernando França Van Dúnem, Joaquim Chissano, Pascoal Mocumbi, Pedro Pires, Onésimo Silveira, Francisco José Tenreiro, Alda do Espírito Santo, Vasco Cabral, Pepetela, Alda Lara e tantos outros. Decorridos, como se disse, cinquenta anos sob a extinção da Casa dos Estudantes do Império, a UCCLA entendeu dever dar um pontapé de saída para homenagear o conjunto desses jovens, tanto mais que Lisboa, que foi sede da Casa dos Estudantes do Império e Coimbra, onde existiu uma delegação, são associadas da UCCLA. No Porto houve também uma delegação durante alguns anos. Esta homenagem corresponde, sem dúvida, a um desígnio comum dos povos de língua oficial portuguesa e não é possível conceber-se o futuro sem a preservação da memória que a todos respeita.Ministério dos Negócios Estrangeiros; Instituto Camões; Jornal SOL; Câmara Municipal de Lisboainfo:eu-repo/semantics/publishedVersio