An Algorithm for Enumerating SRLG Diverse Path Pairs, Journal of Telecommunications and Information Technology, 2010, nr 3

Telecommunication networks are intrinsically multi-layered, a single failure at a lower level usually corresponds to a multi-failure scenario at an upper layer. In this context, the concept of shared risk link group (SRLG) allows an upper layer to select, for a given active path (AP), a backup path (BP), which avoids every SRLG that may involve the selected AP, in the event of a failure. That is a SRLG diverse path set maybe defined as a set of paths, between an origin and a destination, such that no pair of paths can be simultaneously affected by any given failure (or risk) in a single failure scenario. Firstly we present the formulation of the SRLG diverse path pair calculation problem in a directed network. An algorithm for enumerating SRLG diverse paths, by non decreasing cost of their total (additive) cost will be presented, which is based on an algorithm proposed for generating minimal cost node disjoint path pairs. The SRLG diverse path pairs may be node or arc disjoint, with or without length constraints. Computational results will be presented to show the efficiency of the proposed algorithm for obtaining node or arc disjoint SRLG diverse path pairs in undirected networks

A new algorithm for calculating the most reliable pair of disjoint paths in a network, Journal of Telecommunications and Information Technology, 2006, nr 4

In various types telecommunication networks, namely mobile ad hoc networks, WDM networks and MPLS networks, there is the necessity of calculating disjoint paths for given node to node connections in order to increase the reliability of the services supported by these networks. This leads to the problem of calculating a pair of disjoint paths (or a set of disjoint paths) which optimises some measure of performance in those networks. In this paper we present an algorithm, designated as OptDP, for obtaining the most reliable pair of disjoint paths based on the loopless version of MPS, a very efficient k-shortest path algorithm, and on Dijkstra algorithm. Since to the best of our knowledge there is no other proposal of an algorithm capable of solving exactly the same problem we perform a comparison with the application to this problem of the DPSP algorithm which calculates a set of disjoint paths with high reliability. Also a comparison with a simplified version (designated as NopDP) of the proposed algorithm, which stops after a maximal number F of candidate pairs of paths have been found, is presented. The comparison also includes the percentage of cases in which both algorithms were not capable of finding the optimal pair

Analytical properties of a stochastic teletraffic system with MMPP input and an access function, Journal of Telecommunications and Information Technology, 2002, nr 3

Stochastic modeling of teletraffic systems with restricted availability and correlated input arrival rates is of great interest in GoS (grade of service) analysis and design of certain telecommunication networks. This paper presents some analytical properties of a recursive nature, associated with the infinitesimal generator of the Markov process which describes the state of a teletraffic system with MMPP (Markov modulated Poisson process) input traffic, negative exponentially distributed service times, finite queue and restricted availability defined through a loss function. Also the possible application of the derived properties to a direct method of resolution of the linear system, which gives the stationary probability distribution of the system, will be discussed

Hierarchical Multiobjective Routing in MPLS Networks with Two Service Classes – A Meta-Heuristic Solution, Journal of Telecommunications and Information Technology, 2009, nr 3

The paper begins by reviewing a two-level hierarchical multicriteria routing model for MPLS networks with two service classes (QoS and BE services) and alternative routing, as well as the foundations of a heuristic resolution approach, previously proposed by the authors. Afterwards a new approach, of meta-heuristic nature, based on the introduction of simulated annealing and tabu search techniques, in the structure of the dedicated heuristic, is described. The application of the developed procedures to a benchmarking case study will show that, in certain initial conditions, this approach provides improvements in the final results especially in more “difficult” situations detected through sensitivity analysis

Performance Analysisof a Bi-Objective Model for Routing and Wavelength Assignmentin WDM Networks, Journal of Telecommunications and Information Technology, 2010, nr 3

Establishing end-to-end connections on wavelength division multiplexing (WDM) networks requires setting up lightpaths, defining the sequence of optical fibres and the wavelength in each fibre (the routing and wavelength assignment problem) for traffic flow. This paper reviews a bicriteria model for obtaining a topological path (unidirectional or symmetric bidirectional) for each lightpath request in a WDM network, developed by the authors, and presents a performance analysis of the model by considering important network performance measures. An extensive performance analysis of the two bicriteria model is presented, comparing the performance metrics obtained with the monocriterion models using the same objective functions, in five different reference networks commonly used in literature

Implementation and performance of a new multiple objective dynamic routing method for multiexchange networks, Journal of Telecommunications and Information Technology, 2003, nr 3

The paper describes new developments of a multiple objective dynamic routing method (MODR) for circuit-switched networks previously presented, based on the periodic calculation of alternative paths for every node pair by a specialised bi-objective shortest path algorithm (MMRA). A model is presented that enables the numerical calculation of two global network performance parameters, when using MMRA. This model puts in evidence an instability problem in the synchronous path computation model which may lead to solutions with poor global network performance, measured in terms of network mean blocking probability and maximum node-to-node blocking probability. The essential requirements of a heuristic procedure enabling to overcome this problem and select “good” routing solutions in every path updating period, are also discussed

Performance Analysisof a Bi-Objective Model for Routing withProtection in WDM Networks, Journal of Telecommunications and Information Technology, 2010, nr 3

The operation of wavelength division multiplexing (WDM) networks involves not only the establishment of lightpaths, defining the sequence of optical fibres and the wavelength in each fibre for traffic flow, but also a fault management scheme in order to avoid the huge loss of data that can result from a single link failure. Dedicated path protection, which establishes two end-to-end disjoint routes between the source–destination node pair, is an effective scheme to preserve customers’ connections. This paper reviews a bicriteria model for dedicated path protection, that obtains a topological path pair of node-disjoint routes for each lightpath request in a WDM network, developed by the authors. An extensive performance analysis of the bicriteria model is then presented, comparing the performance metrics obtained with the monocriterion models using the same objective functions, in four different reference networks commonly used in literature

On the performance analysis of a heuristic approach dedicated to a multiobjective dynamic routing model, Journal of Telecommunications and Information Technology, 2005, nr 3

In previous works the features and a complete formulation for circuit-switched networks of a multiple objective dynamic routing method (MODR) of periodic state dependent routing type were presented. The aim of the model is to resolve a very complex network bi-objective dynamic routing problem, by recurring to a heuristic for synchronous path selection enabling to obtain a good compromise solution in terms of two network performance measures. In this paper we present a study on the performance of variants of the MODR heuristic of synchronous path selection by using relaxations of the values previously calculated for the two network objective functions. This study permitted the development of an improved version of the initial heuristic. Also a comparison of the analytical values of the network objective functions obtained with selected variants of the initial heuristic with the corresponding results from a known reference method, the real time network routing (RTNR) method, given by a discrete-event simulator for single-service networks, is presented

A new multiple objective dynamic routing method using implied costs, Journal of Telecommunications and Information Technology, 2003, nr 3

There are advantages in considering the routing problem in integrated communication networks as a multiobjective shortest path problem, having in mind to grasp eventual conflicts and trade-offs among distinct objectives and quality of services (QoS) constraints. On the other hand the utilisation of dynamic routing methods in various types of networks is well known to have significant impact on network performance and cost, namely in overload and failure conditions. This paper presents the detailed formulation of a proposal of a multiple objective dynamic routing method (MODR) of periodic state dependent routing type, enabling to represent distinct QoS related metrics and requirements in a consistent manner. The MODR method present formulation is based on a multiple objective shortest path model with constraints and is prepared to use implied costs as one of the metrics. Alternative paths for each traffic flow are changed as a function of periodic updates of certain QoS related parameters estimated from real time measurements on the routes and trunks of the network. Such paths are computed by a specialised and efficient variant of a bi-objective shortest path constrained algorithm, developed for the MODR, enabling to incorporate flexible requirements on the QoS metrics. The architecture of the routing system is discussed together with the features of its main modules. An illustrative example of application of theMODR path calculation module to a circuit-switched type network using blocking probability and implied cost as metrics, is also presented, considering different overload conditions

Traffic splitting in MPLS networks – a hierarchical multicriteria approach, Journal of Telecommunications and Information Technology, 2007, nr 4

In this paper we address a new hierarchical multicriteria routing model associated with a two-path traffic splitting routing method in MPLS networks whereby the bandwidth required by a given node-to-node traffic flow is divided by two disjoint paths. The model has two levels of objective functions and several constraints. An algorithmic approach is presented for calculating non-dominated solutions and selecting good compromise solutions to this problem. Also a number of computational experiments are presented