@misc{OrlowskiPioro, author = {Orlowski, Sebastian and Pi{\´o}ro, Michal}, title = {On the complexity of column generation in survivable network design with path-based survivability mechanisms}, issn = {1438-0064}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-11058}, number = {08-51}, abstract = {This survey concerns optimization problems arising in the design of survivable communication networks. It turns out that such problems can be modeled in a natural way as non-compact linear programming formulations based on multicommodity flow network models. These non-compact formulations involve an exponential number of path flow variables, and therefore require column generation to be solved to optimality. We consider several path-based survivability mechanisms and present results, both known and new, on the complexity of the corresponding column generation problems (called the pricing problems). We discuss results for the case of the single link (or node) failures scenarios, and extend the considerations to multiple link failures. Further, we classify the design problems corresponding to different survivability mechanisms according to the structure of their pricing problem. Finally, we show that almost all encountered pricing problems are hard to solve for scenarios admitting multiple failures.}, language = {en} } @misc{OrlowskiPioroTomaszewskietal., 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}, 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{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} }