José M. F. Craveirinha

Internet packet routing: Application of a K-quickest path algorithm

This paper describes a study on the application of an algorithm to rank the K-quickest paths to the routing of data packets in Internet networks. For this purpose an experimental framework was developed by considering two types of random generated networks. To simulate values of the IP packet sizes, a truncated Pareto distribution was defined, having in mind to reflect a key feature of Internet traffic, namely its self-similar stochastic nature. Results concerning the average CPU times of the algorithm for the different sets of experiments will be presented and discussed.

A bicriterion approach for routing problems in multimedia networks

Routing problems in communication networks supporting multiple services, namely, multimedia applications, involve the selection of paths satisfying multiple constraints (of a technical nature) and seeking simultaneously to “optimize” the associated metrics. Although traditional models in this area are single-objective, in many situations, it is important to consider different, eventually conflicting, objectives. In this paper, we consider a bicriterion model dedicated to calculating nondominated paths for specific traffic flows (associated with video services) in multiservice high-speed networks. The mathematical formulation of the problem and the bicriterion algorithmic approach developed for its resolution are presented together with computational tests regarding an application to video-traffic routing in a high-speed network. The algorithmic approach is an adaptation of recent work by Ernesto Martins and his collaborators, namely, the MPS algorithm.

A meta-model for multiobjective routing in MPLS networks

MPLS (Multiprotocol Label Switching) enables the utilisation of explicit routes and other advanced routing mechanisms in multiservice packet networks, capable of dealing with multiple and heterogeneous QoS (Quality of Service) parameters. Firstly the paper presents a discussion of conceptual and methodological issues raised by multiobjective routing optimisation models for MPLS networks. The major contribution is the proposal of a multiobjective routing optimisation framework for MPLS networks. The major features of this modelling framework are: the formulation of a three-level hierarchical routing optimisation problem including network and service performance objectives, the inclusion of fairness objectives in the different levels of optimisation and a two-level stochastic representation of the traffic in the network (traffic flow and packet stream levels). A variant of the general model for two classes of traffic flows, QoS traffic and Best Effort traffic, is also presented. Finally a stochastic teletraffic modelling approach, underlying the optimisation model, is fully described.

An effective algorithm for obtaining the minimal cost pair of disjoint paths with dual arc costs

Routing optimisation in some types of networks requires the calculation of the minimal cost pair of disjoint paths such that the cost functions associated with the arcs in the two paths are different. An exact algorithm for solving this NP-complete problem is proposed, based on a condition which guarantees that the optimal path pair cost has been obtained. This optimality condition is based on the calculation of upper and lower bounds on the optimal cost. A formal proof of the correctness of the algorithm is described. Extensive experimentation is presented to show the effectiveness of the algorithm, including a comparison with an integer linear programming formulation.

Multicriteria Analysis in Telecommunication Network Planning and Design — Problems and Issues

The interaction between a complex socio-economic environment and the extremely fast pace of development of new telecommunication technologies and services justifies the interest in using multicriteria evaluation in decision making processes associated with several phases of network planning and design. Based on an overview of current and foreseen evolutions in telecommunication network technologies and services we begin by identifying and discussing challenges and issues concerning the use of multicriteria analysis (M.A.) in telecommunication network planning and design problems. Next we present a review of contributions in these areas, with particular emphasis on network modernisation planning and routing problems. We will also outline an agenda of current and future research trends and issues in this application area of multicriteria modelling.

A New Multiobjective Dynamic Routing Method for Multiservice Networks: Modelling and Performance

There are potential advantages in formulating the routing problems in modern multiservice networks as multiple objective problems. This paper presents a novel hierarchical bi-level multiobjective dynamic routing model for multiservice networks. It is based on a bi-objective shortest path algorithm, with dynamically adapted soft-constraints, to compute alternative paths for each node pair and on a heuristic to synchronously select alternative routing plans for the network in a dynamic alternative routing context. It is a routing method which periodically changes alternative paths as a function of periodic updates of certain QoS related parameters obtained from real-time measurements. The performance of the proposed routing method is compared with two reference dynamic routing methods namely RTNR and DAR by means of a discrete-event simulator.

An efficient algorithm for sequential generation of failure states in a network with multi-mode components

Abstract In this work a new algorithm for the sequential generation of failure states in a network with multi-mode components is proposed. The algorithm presented in the paper transforms the state enumeration problem into a K -shortest paths problem. Taking advantage of the inherent efficiency of an algorithm for shortest paths enumeration and also of the characteristics of the reliability problem in which it will be used, an algorithm with lower complexity than the best algorithm in the literature for solving this problem, was obtained. Computational results will be presented for comparing the efficiency of both algorithms in terms of CPU time and for problems of different size.

Planning the evolution to broadband access networks: A multicriteria approach

The interplay between continuing technical innovations, development of multifaceted modes of communication and market structure, among other factors, have raised new and complex problems concerning the strategic modernisation planning of telecommunications networks, namely regarding the evolution paths towards a wide range of new service offerings to be delivered to homes by using broadband technologies. However, decisions must be made by telecommunications operating companies or administrations in a turbulent environment, full of uncertainties with respect to reliable demand forecasts (for new services for which no past data is available), production costs and time to reach the market of some equipment based on brand new technologies, development of new services, etc. Moreover, strategic decisions to be made generally involve distinct, incommensurate and conflicting aspects; that is, problems are multicriteria in nature in the sense that economical, technological, market and social aspects are at stake. Therefore, in order to make well founded decisions, models should explicitly address those different objectives, so that decision makers and planning bodies may grasp the conflicting nature of the objectives and the trade-offs to be made in order to select satisfactory evolution plans. This paper presents a multicriteria model, which extends previous work by the authors, aimed at studying the evolution scenarios to deploy new supporting technologies in the access network to deliver broadband services to individuals and small enterprises.

On a bi-dimensional dynamic alternative routing method

Abstract The analysis of a bi-dimensional dynamic routing model for alternative routing telecommunication networks led to the identification of an instability problem in the synchronous path selection associated with the complex interdependencies among the coefficients of the objective functions and the computed paths for every node pair. In this paper an analytical model enabling to make explicit this problem and evaluate its effects in terms of two global network criteria, is presented. Also a heuristic procedure dedicated to overcome this instability problem and select “good” compromise solutions in terms of network performance is developed. Finally the performance of the proposed routing method using the heuristic is compared by recurring to discrete-event simulation with a reference dynamic routing method (Real Time Network Routing) for some test networks.

Hierarchical multiobjective routing in Multiprotocol Label Switching networks with two service classes: a heuristic solution

Modern multiservice network routing functionalities have to deal with multiple, heterogeneous and multifaceted Quality of Service (QoS) requirements. A heuristic approach devised to find “good” solutions to a hierarchical multiobjective alternative routing optimization problem in Multiprotocol Label Switching networks with two service classes (and different types of traffic flows in each class), namely QoS and Best Effort services, formulated within a hierarchical network-wide optimization framework, is presented. This heuristic solution is based on a bi-objective constrained shortest path model and is applied to a test network used in a benchmarking case study. An experimental study based on analytic and discrete event simulation results is presented, allowing for an assessment of the quality of results obtained with this new heuristic solution for various traffic matrices. A dynamic version of the routing method is formulated and its performance with the same case study network is analysed.