@misc{OrlowskiKosterRaacketal.2006, author = {Orlowski, Sebastian and Koster, Arie M.C.A. and Raack, Christian and Wess{\"a}ly, Roland}, title = {Two-layer Network Design by Branch-and-Cut featuring MIP-based Heuristics}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-9412}, number = {06-47}, year = {2006}, abstract = {This paper deals with MIP-based primal heuristics to be used within a branch-and-cut approach for solving multi-layer telecommunication network design problems. Based on a mixed-integer programming formulation for two network layers, we present three heuristics for solving important subproblems, two of which solve a sub-MIP. On multi-layer planning instances with many parallel logical links, we show the effectiveness of our heuristics in finding good solutions early in the branch-and-cut search tree.}, language = {en} } @misc{RaackKosterWessaely2007, author = {Raack, Christian and Koster, Arie M.C.A. and Wess{\"a}ly, Roland}, title = {On the strength of cut-based inequalities for capacitated network design polyhedra}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-9512}, number = {07-08}, year = {2007}, abstract = {In this paper we study capacitated network design problems, differentiating directed, bidirected and undirected link capacity models. We complement existing polyhedral results for the three variants by new classes of facet-defining valid inequalities and unified lifting results. For this, we study the restriction of the problems to a cut of the network. First, we show that facets of the resulting cutset polyhedra translate into facets of the original network design polyhedra if the two subgraphs defined by the network cut are (strongly) connected. Second, we provide an analysis of the facial structure of cutset polyhedra, elaborating the differences caused by the three different types of capacity constraints. We present flow-cutset inequalities for all three models and show under which conditions these are facet-defining. We also state a new class of facets for the bidirected and undirected case and it is shown how to handle multiple capacity modules by Mixed Integer Rounding (MIR).}, language = {en} } @misc{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}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-9576}, number = {07-14}, year = {2007}, abstract = {This paper deals with directed, bidirected, and undirected capacitated network design problems. Using mixed integer rounding (MIR), we generalize flow-cutset inequalities to these three link types and to an arbitrary modular link capacity structure, and propose a generic separation algorithm. In an extensive computational study on 54 instances from the Survivable Network Design Library (SNDlib), we show that the performance of cplex can significantly be enhanced by this class of cutting planes. The computations reveal the particular importance of the subclass of cutset-inequalities.}, language = {en} } @inproceedings{BleyMenneKlaehneetal.2008, author = {Bley, Andreas and Menne, Ulrich and Kl{\"a}hne, Roman and Raack, Christian and Wess{\"a}ly, Roland}, title = {Multi-layer network design - A model-based optimization approach}, booktitle = {Proceedings of the PGTS 2008, Berlin, Germany}, publisher = {Polish-German Teletraffic Symposium}, address = {Berlin, Germany}, pages = {107 -- 116}, year = {2008}, language = {en} } @misc{OrlowskiPioroTomaszewskietal.2007, author = {Orlowski, Sebastian and Pioro, Michal and Tomaszewski, Artur and Wess{\"a}ly, Roland}, title = {SNDlib 1.0--Survivable Network Design Library}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-9582}, number = {07-15}, year = {2007}, abstract = {We provide information on the Survivable Network Design Library (SNDlib), a data library for fixed telecommunication network design that can be accessed at http://sndlib.zib.de. In version 1.0, the library contains data related to 22 networks which, combined with a set of selected planning parameters, leads to 830 network planning problem instances. In this paper, we provide a mathematical model for each planning problem considered in the library and describe the data concepts of the SNDlib. Furthermore, we provide statistical information and details about the origin of the data sets.}, language = {en} } @misc{MenneRaackWessaelyetal.2012, author = {Menne, Ulrich and Raack, Christian and Wess{\"a}ly, Roland and Kharitonov, Daniel}, title = {Optimal Degree of Optical Circuit Switching in IP-over-WDM Networks}, issn = {1438-0064}, doi = {10.1109/ONDM.2012.6210206}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-14843}, year = {2012}, abstract = {In this paper, we study the influence of technology, traffic properties and price trends on optimized design of a reference IP-over-WDM network with rich underlying fiber topology. In each network node, we investigate the optimal degree of traffic switching in an optical (lambda) domain versus an electrical (packet) domain, also known as measure of \emph{node transparency}. This measure is studied in connection to changes in traffic volume, demand affinity, optical circuit speeds and equipment cost. By applying variable design constraints, we assess the relative roles of the two distinct equipment groups, IP routers and optical cross-connects, with respect to resulting changes in cost-sensitive network architectures.}, language = {en} }