Zespół Sieci Komputerowych

Team leader szef zespołu Krzysztofwalkowiak Krzysztof Walkowiak

Ta strona nie została jeszcze uzupełniona.

Zainteresowania badawcze
  • insert_drive_fileSurvivable multipath routing of anycast and unicast traffic in elastic optical networks ()

    R. Go\'scie\'n and K. Walkowiak and M. Tornatore in Journal of Optical Communications and Networking

    In this paper, we focus on the survivability of elastic optical networks (EONs) that jointly support two types of traffic demands: unicast and anycast. To provide network survivability, we apply multipath routing; i.e., we allow the splitting of a demand into a number of routing paths if the paths’ combination guarantees the realization of a specific demand volume in the case of a single link failure. We formulate the corresponding optimization problem as an integer linear program (ILP) and propose a survivable multipath allocation (SMA) algorithm to solve the problem in a reasonable amount of time. Next, we perform numerical experiments to compare the efficiency (ability to provide a good-quality solution in a reasonable amount of time) of the ILP model and SMA as well as to evaluate the impact of survivable multipath routing on the objective defined as a maximum spectrum usage in EONs. Our results show that the SMA method finds good-quality solutions in a reasonable amount of time and that survivable multipath routing in EONs requires additional spectrum resources, up to 45%. However, the amount of additional resources depends on the required protection level, amount of anycast traffic, the maximum number of paths used for demand realization, and the considered network topology.

    , Cytuj

  • insert_drive_fileProtection in elastic optical networks (2015)

    R. Go\'scie\'n and K. Walkowiak and M. Klinkowski and J. Rak in IEEE Network

    In this article, we analyze gains resulting from the use of EON architectures with special focus on transportation of cloud-ready and content-oriented traffic in the context of network resilience. EONs are a promising approach for future optical transport networks and, apart from improving the network spectral efficiency, bring such new capabilities as squeezed protection, which reduces resource requirements in failure scenarios. In the introductory part, we present a background on new network services based on cloud computing and content orientation paradigms, EON architectures, and their survivability mechanisms. Next, we show the impact of disasters on EON performance. To support the discussion, in the evaluation part we provide simulation results to compare survivable EONs and wavelength-switching optical networks, estimate the efficiency of different survivable EON schemes supporting cloud- and content-oriented traffic, and assess the robustness of EONs to disasters.

    , 2015 Cytuj

  • insert_drive_fileTabu search algorithm for routing, modulation and spectrum allocation in elastic optical network with anycast and unicast traffic (2015)

    R. Go\'scie\'n and K. Walkowiak and M. Klinkowski in Computer Networks

    The paper presents a novel method based on the standard tabu search (TS) approach, dedicated to solve the routing, modulation and spectrum allocation (RMSA) problem in elastic optical networks (EONs). The considered formulation of the RMSA problem covers simultaneously unicast (one-to-one) and anycast (one-to-one-of-many) traffic demands. This is a very important issue taking into account the fact that anycasting gains more and more importance in contemporary Internet due the growing popularity of services like cloud computing, content delivery networks, and video streaming. In this paper, we formulate RMSA as an integer linear programming (ILP) problem and we study four different objective functions, which are related to, respectively, cost, power consumption, maximum and average spectrum usage. We evaluate the performance of our TS method based on the comparison with both optimal results yielded by the CPLEX solver and the results obtained by reference heuristic algorithms proposed in the literature. Moreover, we evaluate benefits of the use of anycasting in EONs. The performed simulation experiments demonstrate that the proposed algorithm outperforms other reference methods. What is more, we show that the anycast transmission can provide significant savings compared to the typical unicast transmission.

    , 2015 Cytuj

  • insert_drive_fileOn the complexity of routing and spectrum assignment in flexible-grid ring networks (2015)

    M. Tornatore and C. Rottondi and R. Go\'scie\'n and K. Walkowiak and G. Rizzelli and A. Morea in Journal of Optical Communications and Networking

    The adoption of a flexible grid will benefit the network design and control plane of future optical networks by providing increased adaptability of spectral resources to heterogeneous network conditions. Unfortunately, this flexibility is gained at the cost of significant additional complexity in the network design and control. In this paper, we consider the optimization of routing and spectrum allocation in flexi-grid ring networks and explore the trade-off between network cost (in terms of spectrum and transponder utilization) and problem complexity (in terms of the number of variables/constraints and computational time). Such trade-offs are investigated under multiple assumptions in terms of traffic grooming, regeneration, and modulation/baud rate assignment capabilities and contrasted with the case of fixed grid. We show how in the presence of traffic grooming the additional complexity due to the flexible grid has a minor impact on problem complexity. Similarly, in all the considered scenarios, regeneration and modulation/baud rate assignment do not relevantly impact on problem complexity. We also consider two possible alternative integer linear programming (ILP) models: the slice-based and channel-based approaches. The former handles each slice individually, whereas the latter uses precomputed subsets of contiguous slices of different bandwidths. Both models are solved under several different network settings. Complexity comparison of the ILP models shows that the slice-based approach provides better performance than the channel-based approach and that the performance gap between the two models increases with the introduction of additional flexibility and dimensions.

    , 2015 Cytuj

  • insert_drive_fileTowards solving practical problems of large solution space using a novel pattern searching hybrid evolutionary algorithm–--an elastic optical network optimization case study (2015)

    M. Przewo\'zniczek and R. Go\'scie\'n and K. Walkowiak and M. Klinkowski in Expert Systems with Applications

    The fast social and economic development observed in the recent years brings up new challenging optimization problems. These problems are often very hard not only because of their computational complexity, but also due to their enormous solution space size. Therefore, this paper proposes an effective optimization method, based on the novel Multi Population Pattern Searching (MuPPetS) Algorithm, to solve optimization problems characterized with very large solution space. As a case study problem, we focus on the problem of routing and spectrum allocation with joint anycast and unicast traffic demands that arises in the field of optical networks optimization. The proposed method is adjusted to the problem with proper solution encoding, hybridization using a local search algorithm, and dedicated mechanisms necessary to improve method convergence. The above adjustments are required to make the method effective against test cases with solution space size of up to 103700 points (sets of values of the choice variables). The paper compares the performance of the proposed method with other reference methods known from the literature. Another key contribution of this paper is presentation of the complicated dependency between fitness function evaluation number (FFE) and real computation load, which are used to evaluate effectiveness of the proposed technique. The analysis is supported with proper empirical tests and their analysis.

    , 2015 Cytuj


Benchmark machine learning dataset repository for Weles.