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

An exact approach for finding bicriteria maximally SRLG-disjoint/shortest path pairs in telecommunication networks

The paper addresses a bicriteria optimisation problem in telecommunication networks that aims at finding Pareto efficient pairs of paths between two given nodes, seeking to minimise the number of SRLGs (Shared Risk Link Groups) common to both paths and the path pair cost. This problem is of particular importance in telecommunication routing design, namely concerning resilient routing models where both a primary and a backup paths have to be calculated to minimise the risk of failure of a connection between origin and terminal nodes, in case of failure in the primary path. An exact resolution method is applied for solving this problem, enabling the calculation of the whole set of Pareto optimal solutions, which combines a transformation of the network representation with a path ranking algorithm. A comprehensive experimental study on the application of this approach, using reference network topologies, considering random SRLG assignments to the links and random link bandwidth occupations, together with the discussion on typical examples of solution selection and potential advantages of the method, are presented

Routage résilient dans les réseaux SDN

International audienceLes réseaux SDN (software-defined networking) permettentàpermettent`permettentà un contrôleur centralisé de décider du routage. Afin d'´ etablir des routes fiables, il est souvent nécessaire de trouver plusieurs chemins dans le réseau ne partageant pas les mêmes ressouresàressoures`ressouresà risque, communément appelé SRLG pour Shared Risk Link Group. Tout en assurant cette fiabilité, l'objectif est aussi de minimiser un coût, qui intègre des indicateurs de congestion ou de latence. Ceprobì eme peutêtrepeutˆpeutêtre modélisé par un programme linéaire en nombres entiers (ILP). Nous proposons ici une méthode efficace pour sa résolution qui utilise une relaxation fractionnaire bien choisie, dont nous montrerons qu'elle m` ene en fait la plupart du tempsàtemps`tempsà une solutionentì ere. La résolution de ceprobì eme relaxé utilise une méthode de génération de colonnes (CG), o` u chaque colonne représente un chemin dans le réseau avec une notion de coût modifié prenant en compte les SRLGs ; les nouvelles colonnes peuventêtrepeuventˆpeuventêtre obtenues par un algorithme efficace de programmation dynamique quí etend les algorithmes classiques de calcul de plus court chemin. Afin de limiter l'explosion combinatoire potentielle, nous présentonsprésentons´présentonségalement une heuristique qui accélére le calcul d'une solution résiliente tout en préservant de très bonnes performances. Les résultats numériques montrent que notre approche donne une solution de très bonne qualité dans un temps de calcul raisonnable sur des instances de réseau réalistes

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

Journal of Telecommunications and Information Technology, 2010, nr 3

kwartalni

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

Future Internet Routing Design for Massive Failures and Attacks

Given the high complexity and increasing traffic load of the Internet, geo-correlated challenges caused by large-scale disasters or malicious attacks pose a significant threat to dependable network communications. To understand its characteristics, we propose a critical-region identification mechanism and incorporate its result into a new graph resilience metric, compensated Total Geographical Graph Diversity. Our metric is capable of characterizing and differentiating resiliency levels for different physical topologies. We further analyze the mechanisms attackers could exploit to maximize the damage and demonstrate the effectiveness of a network restoration plan. Based on the geodiversity in topologies, we present the path geodiverse problem and two heuristics to solve it more efficiently compared to the optimal algorithm. We propose the flow geodiverse problem and two optimization formulations to study the tradeoff among cost, end-to-end delay, and path skew with multipath forwarding. We further integrate the solution to above models into our cross-layer resilient protocol stack, ResTP–GeoDivRP. Our protocol stack is prototyped and implemented in the network simulator ns-3 and emulated in our KanREN testbed. By providing multiple GeoPaths, our protocol stack provides better path restoration performance than Multipath TCP

Supporting differentiated classes of resilience in multilayer networks

Services provided over telecommunications networks typically have different resilience requirements and networks need to be able to support different levels of resilience in an efficient manner. This dissertation investigates the problem of supporting differentiated classes of resilience in multilayer networks, including the most stringent resilience class required by critical services. We incorporate an innovative technique of embedding a subnetwork, termed the spine, with comparatively higher availability values at the physical layer. The spine lays a foundation for differentiation between multiple classes of flows that can be leveraged to achieve both high resilience and differentiation. The aim of this research is mainly to explore, design, and evaluate the proposed spine concept model in multilayer networks. The dissertation has four major parts. First, we explore the spine concept through numerical analysis of simple topologies illustrating the potential benefits and the cost considerations of the spine. We develop heuristics algorithms to find suitable spines for a network based on the structural properties of the network topology. Second, an optimization problem is formulated to determine the spine. The problem encompasses estimates of link availability improvements, associated costs, and a total budget. Third, we propose a crosslayer mapping and spine-aware routing design problem with protection given mainly at the lower layer. The problem is designed to transfer lower layer differentiation capability to the upper layer network and flows. We provide two joint routing-mapping optimization formulations and evaluate their performance in a multilayer scenario. Fourth, the joint routing-mapping problem is redesigned with protection given in the upper network layer instead. This will create two isolated logical networks; one mapped to the spine and the other is mapped freely on the network. Flows are assigned a path or path-pair based on their class of resilience. This approach can provide more routing options yielding different availability levels. The joint routing-mapping design problems are formulated as Integer Linear Programming (ILP) models. The goal is to achieve a wider range of availability values across layers and high availability levels for mission-critical services without the need to use higher order protection configurations. The proposed models are evaluated with extensive numerical results using real network topologies

Resilient routing in the internet

Although it is widely known that the Internet is not prone to random failures, unplanned failures due to attacks can be very damaging. This prevents many organisations from deploying beneficial operations through the Internet. In general, the data is delivered from a source to a destination via a series of routers (i.e routing path). These routers employ routing protocols to compute best paths based on routing information they possess. However, when a failure occurs, the routers must re-construct their routing tables, which may take several seconds to complete. Evidently, most losses occur during this period. IP Fast Re-Route (IPFRR), Multi-Topology (MT) routing, and overlays are examples of solutions proposed to handle network failures. These techniques alleviate the packet losses to different extents, yet none have provided optimal solutions. This thesis focuses on identifying the fundamental routing problem due to convergence process. It describes the mechanisms of each existing technique as well as its pros and cons. Furthermore, it presents new techniques for fast re-routing as follows. Enhanced Loop-Free Alternates (E-LFAs) increase the repair coverage of the existing techniques, Loop-Free Alternates (LFAs). In addition, two techniques namely, Full Fast Failure Recovery (F3R) and fast re-route using Alternate Next Hop Counters (ANHC), offer full protection against any single link failures. Nevertheless, the former technique requires significantly higher computational overheads and incurs longer backup routes. Both techniques are proved to be complete and correct while ANHC neither requires any major modifications to the traditional routing paradigm nor incurs significant overheads. Furthermore, in the presence of failures, ANHC does not jeopardise other operable parts of the network. As emerging applications require higher reliability, multiple failures scenarios cannot be ignored. Most existing fast re-route techniques are able to handle only single or dual failures cases. This thesis provides an insight on a novel approach known as Packet Re-cycling (PR), which is capable of handling any number of failures in an oriented network. That is, packets can be forwarded successfully as long as a path between a source and a destination is available. Since the Internet-based services and applications continue to advance, improving the network resilience will be a challenging research topic for the decades to come

Cálculo de um par de caminhos maximamente disjuntos ou de um par de caminhos disjuntos nas avarias, de custo aditivo mínimo

Atualmente, com o crescente volume de tráfego em redes de telecomunicações, é de extrema importância a proteção das ligações ponto a ponto estabelecidas ao longo da rede, com o objetivo de evitar interrupções de serviço. Um SRLG (Shared Risk Link Group) é um conjunto de elementos da rede que têm um risco comum de falha. Os protocolos de encaminhamento podem distribuir informação acerca dos SRLG que podem afetar cada arco da rede, pelo que se torna importante o desenvolvimento de algoritmos eficientes para a determinação de caminhos disjuntos ou maximamente disjuntos nos SRLG. Um par de caminhos disjuntos nas avarias é um par de caminhos totalmente disjuntos ou que podem ter em comum elementos resilientes, ou seja que estão protegidos numa camada inferior. No presente trabalho, desenvolvido no âmbito de um contrato de I&D com a PT Inovação, foram estudados e implementados vários algoritmos: em primeiro lugar um algoritmo de cálculo de um par de caminhos maximamente disjuntos nos nós, de custo aditivo mínimo, que garante que a solução obtida é ótima; em segundo lugar três algoritmos de cálculo de um par de caminhos maximamente disjuntos nos nós e nos SRLG. Cada um desses três algoritmos, propostos no âmbito deste trabalho, são extensões/adaptações de heurísticas para a determinação de pares de caminhos disjuntos nos SRLG; finalmente foi implementada uma heurística, que procura obter um par de caminhos totalmente disjuntos nos nós, exceto em nós extremos de arcos resilientes partilhados por esse par de caminhos. Os algoritmos foram desenvolvidos tendo em vista a sua utilização em PCE (Path Computation Element) integrados em equipamentos de redes GMPLS (Generalized Multiprotocol Label Switching). Dado que os PCE integrados têm tipicamente recursos computacionais (capacidade de processamento e quantidade de memória) limitados, procurouse otimizar os algoritmos implementados. Foram realizados testes de desempenho das rotinas implementadas, tendo-se verificado que o algoritmo de cálculo de um par de caminhos maximamente disjuntos nos nós, de custo aditivo mínimo, é perfeitamente adequado ao PCE utilizado nos testes. As implementações dos algoritmos de cálculo de um par de caminhos maximamente disjuntos nos nós e nos SRLG, mostraram poder ser utilizadas num PCE no plano de controlo desde que o número de iterações permitido fosse limitado. A última heurística desenvolvida poderá ser utilizada num PCE apenas no plano de gestão uma vez que os tempos de execução não são compatíveis com a sua utilização no plano de controlo, para a rede fornecida pela PT Inovação.Nowadays telecommunication networks face an increasing demand of traffic volume and an increasing need to provide an adequate quality of the service experienced by the users. Therefore the protection of point-to-point connections throughout the network becomes of the utmost importance, in order to avoid service interruptions. A SRLG (Shared Risk Link Group) is a set of network elements with common risk of failure. The routing protocols can consider the information on the SRLG affecting each network link. Therefore, the development of efficient algorithms for the calculation of SRLG-disjoint (or at least maximally disjoint) paths becomes a critical issue in this context. A failure-disjoint path pair is a path pair which is either totally disjoint or only has in common resilient elements (i.e. protected in a lower layer). In this work, which was developed in the context of a R&D contract with PT Inovação, several algorithms were studied and implemented: firstly, an algorithm for the calculation of a maximally node-disjoint path pair of min-sum cost, which guarantees finding an optimal solution; secondly, three algorithms for the calculation of a maximally node and SRLG-disjoint path pair, which are adaptations/extensions of existing heuristics for the calculation of a totally SRLG-disjoint path pair; lastly, a heuristic to calculate a pair of totally node-disjoint paths, except for extreme nodes of resilient links that are shared by that path pair. The algorithms were developed having in mind that they will be used in a PCE (Path Computation Element) in GMPLS (Generalized Multiprotocol Label Switching) networks devices, which are usually very limited in terms of computational resources (processing and memory). Some performance tests for comparison of the implemented algorithms were made. The algorithm for the calculation of maximally node-disjoint path pairs of min-sum cost is suitable for the considered PCE. As for the algorithms for the calculation of maximally node and SRLG-disjoint path pairs, they can be used in a PCE as long as the number of allowed iterations is adequate. The heuristic for the calculation of failure-disjoint path pairs can be used in a PCE but only in a management plane due to its long execution time