@misc{KosterOrlowskiRaacketal., author = {Koster, Arie M.C.A. and Orlowski, Sebastian and Raack, Christian and Bayer, Georg and Engel, Thomas}, title = {Single-layer Cuts for Multi-layer Network Design Problems}, issn = {1438-0064}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-9641}, number = {07-21}, abstract = {We study a planning problem arising in SDH/WDM multi-layer telecommunication network design. The goal is to find a minimum cost installation of link and node hardware of both network layers such that traffic demands can be realized via grooming and a survivable routing. We present a mixed-integer programming formulation that takes many practical side constraints into account, including node hardware, several bitrates, and survivability against single physical node or link failures. This model is solved using a branch-and-cut approach with problem-specific preprocessing and cutting planes based on either of the two layers. On several realistic two-layer planning scenarios, we show that these cutting planes are still useful in the multi-layer context, helping to increase the dual bound and to reduce the optimality gaps.}, language = {en} } @misc{IdzikowskiOrlowskiRaacketal., author = {Idzikowski, Filip and Orlowski, Sebastian and Raack, Christian and Woesner, Hagen and Wolisz, Adam}, title = {Dynamic routing at different layers in IP-over-WDM networks -- Maximizing energy savings}, organization = {Zuse Institute Berlin}, issn = {1438-0064}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-11692}, number = {10-07}, abstract = {We estimate potential energy savings in IP-over-WDM networks achieved by switching off router line cards in low-demand hours. We compare three approaches to react on dynamics in the IP traffic over time, FUFL, DUFL and DUDL. They provide different levels of freedom in adjusting the routing of lightpaths in the WDM layer and the routing of demands in the IP layer. Using MILP models based on three realistic network topologies as well as realistic demands, power, and cost values, we show that already a simple monitoring of the lightpath utilization in order to deactivate empty line cards (FUFL) brings substantial benefits. The most significant savings, however, are achieved by rerouting traffic in the IP layer (DUFL), which allows emptying and deactivating lightpaths together with the corresponding line cards. A sophisticated reoptimization of the virtual topologies and the routing in the optical domain for every demand scenario (DUDL) yields nearly no additional profits in the considered networks. These results are independent of the ratio between the demand and capacity granularities, the time scale and the network topology, and show little dependency on the demand structure.}, language = {en} } @misc{WessaelyWernerEckeletal., author = {Wess{\"a}ly, Roland and Werner, Axel and Eckel, Klaus and Seibel, Julia and Orlowski, Sebastian and Louchet, Hadrien and Patzak, Erwin and Bentz, Winfried}, title = {Sch{\"a}tze heben bei der Planung von FTTx-Netzen: optimierte Nutzung von existierenden Leerrohren - eine Praxisstudie}, issn = {1438-0064}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-14861}, abstract = {Das vom BMBF gef{\"o}rderte Projekt FTTX-PLAN entwickelt mathematische Modelle und Optimierungsverfahren, um automatisiert kostenoptimierte FTTx-Netze berechnen zu k{\"o}nnen. Wir zeigen anhand einer Praxisstudie in Zusammenarbeit mit der Regensburger R-KOM, wie ein Planer von diesen Verfahren profitieren kann, um die Auswirkungen bestimmter Entscheidungen auf die Netzstruktur und -kosten zu untersuchen. Wir illustrieren dies am Beispiel eines FTTB/FTTH-Vergleichs, der Variation von Kundenanbindungsraten und der gezielten Ausnutzung existierender Leerrohre, um Tiefbau zu vermeiden.}, language = {de} } @misc{OrlowskiWernerWessaely, author = {Orlowski, Sebastian and Werner, Axel and Wess{\"a}ly, Roland}, title = {Estimating trenching costs in FTTx network planning}, issn = {1438-0064}, doi = {10.1007/978-3-642-29210-1_15}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-14884}, abstract = {In this paper we assess to which extent trenching costs of an FTTx network are unavoidable, even if technical side constraints are neglected. For that purpose we present an extended Steiner tree model. Using a variety of realistic problem instances we demonstrate that the total trenching cost can only be reduced by about 5 percent in realistic scenarios. This work has been funded by BMBF (German Federal Ministry of Education and Research) within the program "KMU-innovativ".}, language = {en} } @phdthesis{Orlowski, author = {Orlowski, Sebastian}, title = {Optimal Design of Survivable Multi-layer Telecommunication Networks}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-11876}, abstract = {Telecommunication transport networks consist of a stack of technologically different subnetworks, so-called layers, which are strongly interdependent. For example, one layer may correspond to an Internet (IP) backbone network whose links are realized by lightpath connections in an underlying optical fiber layer. To ensure that the network can fulfill its task of routing all communication requests, the inter-layer dependencies have to be taken into account already in the planning phase of the network. This is particularly important with survivability constraints, where connections in one layer have to be protected against cable cuts or equipment failures in another layer. The traditional sequential planning approach where one layer is optimized after the other cannot properly take care of the inter-layer dependencies; this can only be achieved with an integrated planning of several network layers at the same time. This thesis provides mathematical models and algorithmic techniques for the integrated optimization of two network layers with survivability constraints. We describe a multi-layer network design problem which occurs in various technologies, and model it mathematically using mixed-integer programming (MIP) formulations. The presented models cover many important practical side constraints from different technological contexts. In contrast to previous models from the literature, they can be used to design large two-layer networks with survivability requirements. We discuss modeling alternatives for various aspects of a multi-layer network and compare different routing formulations under multi-layer survivability constraints. We solve our models using a branch-and-cut-and-price approach with various problemspecific enhancements. This includes a presolving technique based on linear programming to reduce the problem size, combinatorial and sub-MIP-based primal heuristics to compute feasible network configurations, cutting planes which take the multi-layer survivability constraints into account to improve the lower bound on the optimal network cost, and column generation to generate flow variables dynamically during the algorithm. We develop techniques to speed up computations in a Benders decomposition approach and compare this approach to the standard formulation with a single MIP. We use the developed techniques to design large survivable two-layer networks by means of linear and integer programming methods. On realistic test instances with up to 67 network nodes and survivability constraints, we investigate the algorithmic impact of our techniques and show how to use them to compute good network configurations with quality guarantees. Most of the smaller test instances with up to 17 nodes can be solved to near-optimality. Moreover, we can compute feasible solutions and dual bounds even for large networks with survivability constraints, which has not been possible before.}, language = {en} } @article{RaackKosterOrlowskietal.2011, author = {Raack, Christian and Koster, Arie M.C.A. and Orlowski, Sebastian and Wess{\"a}ly, Roland}, title = {On cut-based inequalities for capacitated network design polyhedra}, series = {Networks}, volume = {57}, journal = {Networks}, number = {2}, pages = {141 -- 156}, year = {2011}, language = {en} } @article{IdzikowskiOrlowskiRaacketal.2011, author = {Idzikowski, Filip and Orlowski, Sebastian and Raack, Christian and Woesner, Hagen and Wolisz, Adam}, title = {Dynamic routing at different layers in IP-over-WDM networks - Maximizing energy savings}, series = {Optical Switching and Networking, Special Issue on Green Communications}, journal = {Optical Switching and Networking, Special Issue on Green Communications}, year = {2011}, language = {en} } @inproceedings{IdzikowskiOrlowskiRaacketal.2010, author = {Idzikowski, Filip and Orlowski, Sebastian and Raack, Christian and Woesner, Hagen and Wolisz, Adam}, title = {Saving energy in IP-over-WDM networks by switching off line cards in low-demand scenarios}, series = {Proceedings of the 14th conference on Optical network design and modeling}, booktitle = {Proceedings of the 14th conference on Optical network design and modeling}, publisher = {IEEE Press}, address = {Piscataway, NJ, USA}, pages = {42 -- 47}, year = {2010}, language = {en} } @incollection{KosterOrlowskiRaacketal.2009, author = {Koster, Arie M.C.A. and Orlowski, Sebastian and Raack, Christian and Baier, Georg and Engel, Thomas and Belotti, Pietro}, title = {Branch-and-cut techniques for solving realistic two-layer network design problems}, series = {Graphs and Algorithms in Communication Networks}, booktitle = {Graphs and Algorithms in Communication Networks}, publisher = {Springer Berlin Heidelberg}, pages = {95 -- 118}, year = {2009}, language = {en} } @inproceedings{RaackKosterOrlowskietal.2007, author = {Raack, Christian and Koster, Arie M.C.A. and Orlowski, Sebastian and Wess{\"a}ly, Roland}, title = {Capacitated network design using general flow-cutset inequalities}, series = {Proceedings of the INOC 2007, Spa, Belgium, also ZIB Report ZR-07-14}, booktitle = {Proceedings of the INOC 2007, Spa, Belgium, also ZIB Report ZR-07-14}, publisher = {International Network Optimization Conference}, address = {Spa, Belgium}, year = {2007}, language = {en} }