@misc{BleyKoch, author = {Bley, Andreas and Koch, Thorsten}, title = {Optimierung in der Planung und beim Aufbau des G-WiN}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-6169}, number = {00-48}, abstract = {Ende Juni diesen Jahres wurde das Gigabit-Wissenschaftsnetz offiziell gestartet. In der zweij{\"a}hrigen Vorbereitungsphase wurden nicht nur die technischen M{\"o}glichkeiten der neuen {\"U}bertragungstechniken und Dienste getestet. Es wurden auch verschiedene Fragestellungen zum effizienten Einsatz der verf{\"u}gbaren Ressourcen f{\"u}r den Betrieb des G-WiN untersucht. In diesem Artikel beschreiben wir, wie das G-WiN zu seiner jetzigen Struktur und Topologie gekommen ist.}, language = {de} } @misc{BleyKoch, author = {Bley, Andreas and Koch, Thorsten}, title = {Integer programming approaches to access and backbone IP-network planning}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-7081}, number = {02-41}, abstract = {In this article we study the problem of designing a nation-wide communication network. Such networks usually consist of an access layer, a backbone layer, and maybe several intermediate layers. The nodes of each layer must be connected to those of the next layer in a tree-like fashion. The backbone layer has to satisfy certain survivability and routing constraints. Given the node locations, the demands between them, the possible connections and hardware configurations, and various other technical and administrational constraints, the goal is to decide, which node is assigned to which network level, how the nodes are connected, what hardware must be installed, and how traffic is routed in the backbone. Mixed integer linear programming models and solution methods are presented for both the access and the backbone network design problem. The focus is on the design of IP-over-SDH networks, but the access network design model and large parts of the backbone network design models are general and also applicable for other types of communication networks. Results obtained with these methods in the planning of the German research network are presented.}, language = {en} } @misc{Bley, author = {Bley, Andreas}, title = {Inapproximability Results for the Inverse Shortest Paths Problem with Integer Length and Unique Shortest Paths}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-8388}, number = {05-04}, abstract = {We study the complexity of two Inverse Shortest Paths (ISP) problems with integer arc lengths and the requirement for uniquely determined shortest paths. Given a collection of paths in a directed graph, the task is to find positive integer arc lengths such that the given paths are uniquely determined shortest paths between their respective terminals. The first problem seeks for arc lengths that minimize the length of the longest of the prescribed paths. In the second problem, the length of the longest arc is to be minimized. We show that it is \$np-hard\$ to approximate the minimal longest path length within a factor less than \$8/7\$ or the minimal longest arc length within a factor less than \$9/8\$. This answers the (previously) open question whether these problems are \$np-hard\$ or not. We also present a simple algorithm that achieves an \$\mathcal{O}(|V|)\$-approximation guarantee for both variants. Both ISP problems arise in the planning of telecommunication networks with shortest path routing protocols. Our results imply that it is \$\mathcal{NP}\$-hard to decide whether a given path set can be realized with a real shortest path routing protocol such as OSPF, IS-IS, or RIP.}, language = {en} } @misc{BleyKochNiu, author = {Bley, Andreas and Koch, Thorsten and Niu, Lingfeng}, title = {Experiments with nonlinear extensions to SCIP}, issn = {1438-0064}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-8300}, number = {08-28}, abstract = {This paper describes several experiments to explore the options for solving a class of mixed integer nonlinear programming problems that stem from a real-world mine production planning project. The only type of nonlinear constraints in these problems are bilinear equalities involving continuous variables, which enforce the ratios between elements in mixed material streams. A branch-and-bound algorithm to handle the integer variables has been tried in another project. However, this branch-and-bound algorithm is not effective for handling the nonlinear constraints. Therefore state-of-the-art nonlinear solvers are utilized to solve the resulting nonlinear subproblems in this work. The experiments were carried out using the NEOS server for optimization. After finding that current nonlinear programming solvers seem to lack suitable preprocessing capabilities, we preprocess the instances beforehand and use an heuristic approach to solve the nonlinear subproblems. In the appendix, we explain how to add a polynomial constraint handler that uses IPOPT as embedded nonlinear programming solver for the constraint programming framework SCIP. This is one of the crucial steps for implementing our algorithm in SCIP. We briefly described our approach and give an idea of the work involved.}, language = {en} } @misc{BleyPattloch, author = {Bley, Andreas and Pattloch, Marcus}, title = {Modellierung und Optimierung der X-WiN Plattform}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-8551}, number = {05-21}, abstract = {In diesem Artikel werden die Optimierungsmodelle und -verfahren beschrieben, die bei der Planung des Kernnetzes und der Zugangsinfrastruktur des X-WiN verwendet wurden.}, language = {de} } @misc{Bley, author = {Bley, Andreas}, title = {A Lagrangian Approach for Integrated Network Design and Routing in IP Networks}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-7515}, number = {03-29}, abstract = {We consider the problem of designing a network that employs a non-bifurcated shortest path routing protocol. The network's nodes and the set of potential links are given together with a set of forecasted end-to-end traffic demands. All relevant hardware components installable at links or nodes are considered. The goal is to simultaneously choose the network's topology, to decide which hardware components to install on which links and nodes, and to find appropriate routing weights such that the overall network cost is minimized. In this paper, we present a mathematical optimization model for this problem and an algorithmic solution approach based on a Lagrangian relaxation. Computational results achieved with this approach for several real-world network planning problems are reported.}, language = {en} } @misc{BleyKosterKroelleretal., author = {Bley, Andreas and Koster, Arie M.C.A. and Kr{\"o}ller, Alexander and Wess{\"a}ly, Roland and Zymolka, Adrian}, title = {Kosten- und Qualit{\"a}tsoptimierung in Kommunikationsnetzen}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-7537}, number = {03-31}, abstract = {Der scharfe Wettbewerb innerhalb der Telekommunikationsbranche zwingt die Netzbetreiber dazu, ihre Investitionen genau zu planen und immer wieder Einsparungsmanahmen durchzuf{\"u}hren. Gleichzeitig ist es jedoch wichtig, die Qualit{\"a}t der angebotenen Dienste zu verbessern, um neue Kunden zu gewinnen und langfristig an sich zu binden. Die mathematische Optimierung bietet sich f{\"u}r viele solcher Aufgabenstellungen als hervorragend geeignetes Planungswerkzeug an. Ziel dieses Artikels ist es, ihre Methodik und ihre Anwendung speziell zur Kosten- und Qualit{\"a}tsoptimierung in Kommunikationsnetzen vorzustellen. Anhand von vier konkreten Planungsaufgaben aus dem Bereich der Festnetzplanung wird aufgezeigt, wie sich komplexe Zusammenh{\"a}nge in flexiblen mathematischen Modellen abbilden lassen und welche Verfahren zur automatisierten Bearbeitung der Probleme eingesetzt werden k{\"o}nnen. Die hier vorgestellten Methoden zeichnen sich insbesondere dadurch aus, dass sie neben hochwertigen L{\"o}sungen auch eine Qualittsgarantie liefern, mit der sich die Lsungen fundiert bewerten lassen. Die dokumentierten Ergebnisse aus verschiedenen Industrieprojekten belegen die Eignung und G{\"u}te der mathematischen Optimierung f{\"u}r die Praxis.}, language = {de} } @misc{BleyZymolka, author = {Bley, Andreas and Zymolka, Adrian}, title = {Planung kostenoptimaler Informations- und Kommunikations-Infrastrukturen}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-7591}, number = {03-37}, abstract = {Beim Entwurf und Ausbau von Informations- und Kommunikationsnetzwerken m{{\"u}}ssen zahlreiche interdependente Entscheidungen getroffen und gleichzeitig mannigfaltige Bedingungen ber{{\"u}}cksichtigt werden. Die verf{{\"u}}gbaren technischen und organisatorischen Alternativm{{\"o}}glichkeiten sind normalerweise so vielf{{\"a}}ltig und komplex, dass eine manuelle Planung praktisch nicht m{{\"o}}glich ist. In diesem Artikel wird das Potential und die Methodik der mathematischen Optimierung bei der kostenoptimalen Planung von Kommunikationsnetzen vorgestellt. Als Ausgangspunkt wird exemplarisch eine typische praktische Aufgabe, die Struktur- und Konfigurationsplanung mehrstufiger Telekommunikationsnetzwerke, dargestellt. Anschließend werden kurz die wesentlichen Modellierungstechniken und Verfahrensans{{\"a}}tze der mathematischen Optimierung skizziert. Abschließend gehen wir auf die Planung einer ad{{\"a}}quaten Informations- und Kommunikations- Infrastruktur f{{\"u}}r ein dezentrales Energieversorgungsnetz ein.}, language = {de} } @misc{BleyKochWessaely, author = {Bley, Andreas and Koch, Thorsten and Wess{\"a}ly, Roland}, title = {Large-scale hierarchical networks: How to compute an optimal architecture?}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-7799}, number = {04-04}, abstract = {In this article, we present a mathematical model and an algorithm to support one of the central strategic planning decisions of network operators: How to organize a large number of locations into a hierarchical network? We propose a solution approach that is based on mixed-integer programming and Lagrangian relaxation techniques. As major advantage, our approach provides not only solutions but also worst-case quality guarantees. Real-world scenarios with more than 750 locations have been solved within 30 minutes to less than 1\\% off optimality.}, language = {en} } @misc{Bley, author = {Bley, Andreas}, title = {On the Hardness of Finding Small Shortest Path Routing Conflicts}, issn = {1438-0064}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-11276}, number = {09-15}, abstract = {Nowadays most data networks use shortest path protocols such as OSPF or IS-IS to route traffic. Given administrative routing lengths for the links of a network, all data packets are sent along shortest paths with respect to these lengths from their source to their destination. One of the most fundamental problems in planning shortest path networks is to decide whether a given set of routing paths forms a valid routing and, if this is not the case, to find a small subset of the given paths that cannot be shortest paths simultaneously for any routing lengths. In this paper we show that it is NP-hard to approximate the size of the smallest shortest path conflict by a factor less than 7/6.}, language = {en} }