@article{MuRySpKo2016-PASM-QPN-LQN-Transformation,
title = {{Enabling Fluid Analysis for Queueing Petri Nets via Model Transformation}},
journal = {Electronic Notes in Theoretical Computer Science},
volume = {327},
pages = {71--91},
year = {2016},
publisher = {Elsevier},
note = {The 8th International Workshop on Practical Application of Stochastic Modeling, PASM 2016},
issn = {1571-0661},
doi = {10.1016/j.entcs.2016.09.024},
url = {http://www.sciencedirect.com/science/article/pii/S157106611630069X},
  author = {Christoph M\"{u}ller and Piotr Rygielski and Simon Spinner and Samuel Kounev},
abstract = {Abstract Due to the growing size of modern \{IT\} systems, their performance analysis becomes an even more challenging task. Existing simulators are unable to analyze the behavior of large systems in a reasonable time, whereas analytical methods suffer from the state space explosion problem. Fluid analysis techniques can be used to approximate the solution of high-order Markov chain models enabling time efficient analysis of large performance models. In this paper, we describe a model-to-model transformation from queueing Petri nets (QPN) into layered queueing networks (LQN). Obtained \{LQN\} models can benefit from three existing solvers: LINE, LQNS, LQSIM. \{LINE\} internally utilize fluid limits approximation to speed up the solving process for large models. We present the incentives for developing the automated model-to-model transformation and present a systematic approach that we followed in its design. We demonstrate the transformations using representative examples. Finally, we evaluate and compare the performance predictions of existing analytical, simulation and fluid analysis solvers. We analyze solvers' limitations, solving time, and memory consumption.},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/1075.pdf},
  slides = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/slides/1075},
}

Abstract Due to the growing size of modern \{IT\} systems, their performance analysis becomes an even more challenging task. Existing simulators are unable to analyze the behavior of large systems in a reasonable time, whereas analytical methods suffer from the state space explosion problem. Fluid analysis techniques can be used to approximate the solution of high-order Markov chain models enabling time efficient analysis of large performance models. In this paper, we describe a model-to-model transformation from queueing Petri nets (QPN) into layered queueing networks (LQN). Obtained \{LQN\} models can benefit from three existing solvers: LINE, LQNS, LQSIM. \{LINE\} internally utilize fluid limits approximation to speed up the solving process for large models. We present the incentives for developing the automated model-to-model transformation and present a systematic approach that we followed in its design. We demonstrate the transformations using representative examples. Finally, we evaluate and compare the performance predictions of existing analytical, simulation and fluid analysis solvers. We analyze solvers' limitations, solving time, and memory consumption.

@article{MiIoKoSaMuCuDiRoRy2016-IEEECC-cup,
author = {Aleksandar Milenkoski and Alexandru Iosup and Samuel Kounev and Kai Sachs and Diane E. Mularz and Jonathan A. Curtiss and Jason J. Ding and Florian Rosenberg and Piotr Rygielski},
title = {{CUP: A Formalism for Expressing Cloud Usage Patterns for Experts and Non-Experts}},
journal = {IEEE Cloud Computing},
year = {2016},
note = {To Appear}
}

@article{RyKo2013,
  author = {Piotr Rygielski and Samuel Kounev},
  doi = {http://dx.doi.org/10.1515/pik-2012-0136},
  journal = {PIK --- Praxis der Informationsverarbeitung und Kommunikation},
  month = {February},
  number = {1},
  pages = {55--64},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/559.pdf},
  publisher = {de Gruyter},
  title = {{Network Virtualization for QoS-Aware Resource Management in Cloud Data Centers: A Survey}},
  url = {http://www.degruyter.com/view/j/piko-2013-36-issue-1/pik-2012-0136/pik-2012-0136.xml?format=INT},
  volume = {36},
  year = {2013},
  abstract = {The increasing popularity of Cloud Computing is leading to the emergence of large virtualized data centers hosting increasingly complex and dynamic IT systems and services. Over the past decade, the efficient sharing of computational resources through virtualization has been subject to intensive research, while network management in cloud data centers has received less attention. A variety of network-intensive applications require QoS (Quality-of-Service) provisioning, performance isolation and support for flexible and efficient migration of virtual machines. In this paper, we survey existing network virtualization approaches and evaluate the extent to which they can be used as a basis for realizing the mentioned requirements in a cloud data center. More specifically, we identify generic network virtualization techniques, characterize them according to their features related to QoS management and performance isolation, and show how they can be composed together and used as building blocks for complex network virtualization solutions. We then present an overview of selected representative cloud platforms and show how they leverage the generic techniques as a basis for network resource management. Finally, we outline open issues and research challenges in the area of performance modeling and proactive resource management of virtualized data center infrastructures.},
}

The increasing popularity of Cloud Computing is leading to the emergence of large virtualized data centers hosting increasingly complex and dynamic IT systems and services. Over the past decade, the efficient sharing of computational resources through virtualization has been subject to intensive research, while network management in cloud data centers has received less attention. A variety of network-intensive applications require QoS (Quality-of-Service) provisioning, performance isolation and support for flexible and efficient migration of virtual machines. In this paper, we survey existing network virtualization approaches and evaluate the extent to which they can be used as a basis for realizing the mentioned requirements in a cloud data center. More specifically, we identify generic network virtualization techniques, characterize them according to their features related to QoS management and performance isolation, and show how they can be composed together and used as building blocks for complex network virtualization solutions. We then present an overview of selected representative cloud platforms and show how they leverage the generic techniques as a basis for network resource management. Finally, we outline open issues and research challenges in the area of performance modeling and proactive resource management of virtualized data center infrastructures.

@article{SwRyJuGr2012-CBS,
  address = {Bristol, PA, USA},
  author = {Pawe{l} \'{S}wi\k{a}tek and Piotr Rygielski and Krzysztof Juszczyszyn and Adam Grzech},
  isbn = {0196-9722},
  journal = {{Cybernetics and Systems: An International Journal (CBS)}},
  month = {May},
  number = {4},
  pages = {340--353},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/682.pdf},
  publisher = {Taylor & Francis, Inc.},
  title = {{User Assignment and Movement Prediction in Wireless Networks}},
  url = {http://www.tandfonline.com/doi/abs/10.1080/01969722.2012.678219},
  volume = {43},
  note = {5-Year Impact Factor (2014): 0.968},
  year = {2012},
  abstract = {The article is devoted to the problem of mobility and resource management in heterogeneous wireless networks. It is assumed that in certain areas covered by multiple overlapping wireless networks there are a certain number of mobile clients that consume networks resources by use of the available communication services (e.g., voice or data transmission) delivered by network providers. Moreover, it is assumed that the continuity of communication services may be assured by the use of common handover techniques supporting client mobility (e.g., Mobile IPv6, IEEE 802.21, etc.). The task of mobility and resource management consists of making decisions concerning the moment and the network to which particular clients should be handed over in order to optimize certain quality criterion (e.g., utilization of network resources). In this article we show that gathering knowledge about client movements and prediction of their future positions may significantly improve the overall quality of the services delivered and network resource utilization.},
}

The article is devoted to the problem of mobility and resource management in heterogeneous wireless networks. It is assumed that in certain areas covered by multiple overlapping wireless networks there are a certain number of mobile clients that consume networks resources by use of the available communication services (e.g., voice or data transmission) delivered by network providers. Moreover, it is assumed that the continuity of communication services may be assured by the use of common handover techniques supporting client mobility (e.g., Mobile IPv6, IEEE 802.21, etc.). The task of mobility and resource management consists of making decisions concerning the moment and the network to which particular clients should be handed over in order to optimize certain quality criterion (e.g., utilization of network resources). In this article we show that gathering knowledge about client movements and prediction of their future positions may significantly improve the overall quality of the services delivered and network resource utilization.

@article{PT2011-kompozycja,
author = {Krzysztof Brzostowski and Piotr Rygielski},
title = {Automatyczna kompozycja uslug monitorowania dla systemu wspomagania treningu wytrzymalo\'sciowego sportowc\'ow},
journal = {Przegl\k{a}d Telekomunikacyjny, Wiadomo\'sci Telekomunikacyjne},
volume = {84},
issue = {8/9},
pages = {1017--1022},
note = {In Polish},
year = {2011},
pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/777.pdf}
}

@article{GrSwRy2010-CBS,
  address = {Bristol, PA, USA},
  author = {Adam Grzech and Pawel \'{S}wi\k{a}tek and Piotr Rygielski},
  issn = {0196-9722},
  journal = {{Cybernetics and Systems: An International Journal (CBS)}},
  month = {November},
  number = {8},
  pages = {610--627},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/676.pdf},
  publisher = {Taylor & Francis, Inc.},
  title = {Translations of Service Level Agreement in Systems Based on Service Oriented Architectures},
  url = {http://dx.doi.org/10.1080/01969722.2010.520225},
  volume = {41},
  year = {2010},
  note = {5-Year Impact Factor (2014): 0.968},
  abstract = {The gain of the article is to introduce and to discuss a formal specification of a computer system's service level agreement (SLA) and its translation into the structure of complex services (composed of atomic services) delivering required functionalities and nonfunctionalities in a distributed environment. It is assumed that the SLA is composed of two parts specifying quantitative and qualitative requirements. The former requirements define the structure of the adequate complex services in form of a directed graph, where potential parallelism of atomic services performance may be taken into account. The latter qualitative requirements are applied to select the optimal complex service realization scenario; it is based on assumption that various atomic services distinguished in the complex services structures are available at the considered distributed environment in different versions and locations. Different versions of atomic services are atomic services delivering the required functionalities and satisfy non-functionalities at various levels. Different locations (installation place) of available atomic services means that the cost of atomic services delivery (communication and calculation) depends on parts of the distributed systems where the services are performed. The proposed model of SLA translation into complex services structures and variants may be applied among others to calculate upper and lower complex services delivery times and to estimate the validity of possible parallelism in complex services.},
}

The gain of the article is to introduce and to discuss a formal specification of a computer system's service level agreement (SLA) and its translation into the structure of complex services (composed of atomic services) delivering required functionalities and nonfunctionalities in a distributed environment. It is assumed that the SLA is composed of two parts specifying quantitative and qualitative requirements. The former requirements define the structure of the adequate complex services in form of a directed graph, where potential parallelism of atomic services performance may be taken into account. The latter qualitative requirements are applied to select the optimal complex service realization scenario; it is based on assumption that various atomic services distinguished in the complex services structures are available at the considered distributed environment in different versions and locations. Different versions of atomic services are atomic services delivering the required functionalities and satisfy non-functionalities at various levels. Different locations (installation place) of available atomic services means that the cost of atomic services delivery (communication and calculation) depends on parts of the distributed systems where the services are performed. The proposed model of SLA translation into complex services structures and variants may be applied among others to calculate upper and lower complex services delivery times and to estimate the validity of possible parallelism in complex services.

@article{GrSwRy2010-SS,
  address = {Wroclaw, Poland},
  author = {Adam Grzech and Pawel \'Swi\k{a}tek and Piotr Rygielski},
  journal = {Systems Science},
  number = {1},
  pages = {7--12},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/674.pdf},
  publisher = {Wroclaw University of Technology Press},
  title = {{Adaptive Packet Scheduling for Requests Delay Guaranties in Packet-Switched Communication Network}},
  url = {http://linksource.ebsco.com/linking.aspx?issn=0137-1223&volume=36&spage=7},
  volume = {36},
  year = {2010},
  abstract = {In this paper the problem of packet scheduling in the node of packet-switched computer communication network is considered. Packet scheduling in the network edge nodes is one of the crucial mechanisms essential for delivery of required level of quality of end-to-end network services (QoS). In order to satisfy QoS guaranties for each incoming request belonging to one of distinguished traffic classes, packet scheduling algorithm must make decisions based on current state of the scheduling system (e.g. buffer lengths) and actual characteristics of the serviced traffic (e.g.: lengths of connections following requests, packet intensities within requests, etc.). The paper is devoted to propose a new packet scheduling algorithm based on Weighted Round Robin (WRR), which weights are adapted according to changes of network’s load and traffic characteristics. By means of computer simulation, on representative examples, it was shown, that utilization of additional knowledge about incoming traffic in the process of packet scheduling may improve QoS guaranties for serviced traffic.},
}

In this paper the problem of packet scheduling in the node of packet-switched computer communication network is considered. Packet scheduling in the network edge nodes is one of the crucial mechanisms essential for delivery of required level of quality of end-to-end network services (QoS). In order to satisfy QoS guaranties for each incoming request belonging to one of distinguished traffic classes, packet scheduling algorithm must make decisions based on current state of the scheduling system (e.g. buffer lengths) and actual characteristics of the serviced traffic (e.g.: lengths of connections following requests, packet intensities within requests, etc.). The paper is devoted to propose a new packet scheduling algorithm based on Weighted Round Robin (WRR), which weights are adapted according to changes of network’s load and traffic characteristics. By means of computer simulation, on representative examples, it was shown, that utilization of additional knowledge about incoming traffic in the process of packet scheduling may improve QoS guaranties for serviced traffic.

@article{RySw2010-SS,
  address = {Wroclaw, Poland},
  author = {Piotr Rygielski and Pawel \'Swi\k{a}tek},
  journal = {Systems Science},
  number = {3},
  pages = {25--32},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/677.pdf},
  publisher = {Wroclaw University of Technology Press},
  title = {{Graph-fold: an Efficient Method for Complex Service Execution Plan Optimization}},
  url = {http://linksource.ebsco.com/linking.aspx?issn=0137-1223&volume=36&spage=25},
  volume = {36},
  year = {2010},
  abstract = {The task of optimization of the complex service execution plan is the last stage of the process of complex services composition in systems based on the SOA paradigm. In general this task consists of choosing proper versions of atomic services, delivering requested functionalities, such that non-functional requirements for complex service are satisfied. In most real-life cases this task is reduced to the problem of multidimensional knapsack problem (MKP), which is known to be NP-hard. Therefore, in order to facilitate effective complex service composition, it is crucial to provide an efficient MKP solution algorithm. In this paper a novel approach to the problem of optimization of complex service execution plan is introduced. In the proposed approach the MKP feasible solution space is constructed in such a way, that the optimal solution can be found in constant time. Of course, since MKP is NP-hard, the process of solution space construction takes an exponential time, This time, however, is amortized by multiple usages of single solution space for determination of optimal execution plans for multiple complex service requests.},
}

The task of optimization of the complex service execution plan is the last stage of the process of complex services composition in systems based on the SOA paradigm. In general this task consists of choosing proper versions of atomic services, delivering requested functionalities, such that non-functional requirements for complex service are satisfied. In most real-life cases this task is reduced to the problem of multidimensional knapsack problem (MKP), which is known to be NP-hard. Therefore, in order to facilitate effective complex service composition, it is crucial to provide an efficient MKP solution algorithm. In this paper a novel approach to the problem of optimization of complex service execution plan is introduced. In the proposed approach the MKP feasible solution space is constructed in such a way, that the optimal solution can be found in constant time. Of course, since MKP is NP-hard, the process of solution space construction takes an exponential time, This time, however, is amortized by multiple usages of single solution space for determination of optimal execution plans for multiple complex service requests.

@inproceedings{RySeKoKl2016-valuetools2016-sdn-switches-hw-sw-flow-tables,
  author = {Piotr Rygielski and Marian Seliuchenko and Samuel Kounev and Mykhailo Klymash},
  title = {{Performance Analysis of SDN Switches with Hardware and Software Flow Tables}},
  booktitle = {Proceedings of the 10th EAI International Conference on Performance Evaluation Methodologies and Tools (ValueTools 2016)},
  year = {2016},
  month = {October}, 
  day = {25--28},
  abstract = {{Nowadays data centers are increasingly becoming larger and dynamic due to virtualization. Software-Defined Networking is the leading approach to network virtualization and flexible management. The wide variety of hardware implementations have brought strong heterogeneity to the market of networking devices which are different in terms of OpenFlow features and performance. In this paper we address the issue of heterogeneity of four hardware OpenFlow switches by characterizing selected performance relevant parameters for the hardware and software flow tables. We characterize maximum size of hardware flow tables for each switch including the behavior of a rule promotion engine that moves the rules between tables. We show that in the worst case forwarding packets using software table decreases the throughput by two orders of magnitude (from 940 to 14 Mbit/s). Our results can help the developers of SDN applications to account performance limitations of hardware and software processing as well as limited hardware support for a specific rule types. }},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/1132.pdf},
}

{Nowadays data centers are increasingly becoming larger and dynamic due to virtualization. Software-Defined Networking is the leading approach to network virtualization and flexible management. The wide variety of hardware implementations have brought strong heterogeneity to the market of networking devices which are different in terms of OpenFlow features and performance. In this paper we address the issue of heterogeneity of four hardware OpenFlow switches by characterizing selected performance relevant parameters for the hardware and software flow tables. We characterize maximum size of hardware flow tables for each switch including the behavior of a rule promotion engine that moves the rules between tables. We show that in the worst case forwarding packets using software table decreases the throughput by two orders of magnitude (from 940 to 14 Mbit/s). Our results can help the developers of SDN applications to account performance limitations of hardware and software processing as well as limited hardware support for a specific rule types. }

@inproceedings{RySeKo2016-SIMUTools-SDN-switches-QPN,
  title = {{Modeling and Prediction of Software-Defined Networks Performance using Queueing Petri Nets}},
  year = {2016},
  month = {August},
  days = {22--23},
  pages={66--75},
  location = {Prague, Czech Republic},
  booktitle = {Proceedings of the Ninth International Conference on Simulation Tools and Techniques (SIMUTools 2016)},
  author = {Piotr Rygielski and Marian Seliuchenko and Samuel Kounev},
  abstract = {{Using various modeling and simulation approaches for predicting network performance requires extensive experience and involves a number of time consuming manual steps regarding each of the modeling formalisms. Descartes Network Infrastructure (DNI) is a data center network performance modeling approach that addresses this challenge by offering multiple performance models but requiring to use only a single modeling language. In this paper, we thoroughly extend DNI to support new networking paradigms like, among others, Software-Defined Networking (SDN) and Network-Function Virtualization (NFV). Additionally, we demonstrate how SDN-based networks can be modeled using DNI and how are they transformed later into Queueing Petri Nets (QPN) using a model-to-model transformation. In the analysis of the performance prediction accuracy, we show that automatically generated QPN models represent the performance of heterogeneous SDN hardware with maximal prediction accuracy error of 12 percent.}},
 isbn = {978-1-63190-120-1}, 
  url = {http://dl.acm.org/citation.cfm?id=3021426.3021437},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/1120.pdf},
  slides = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/slides/1120},
}

{Using various modeling and simulation approaches for predicting network performance requires extensive experience and involves a number of time consuming manual steps regarding each of the modeling formalisms. Descartes Network Infrastructure (DNI) is a data center network performance modeling approach that addresses this challenge by offering multiple performance models but requiring to use only a single modeling language. In this paper, we thoroughly extend DNI to support new networking paradigms like, among others, Software-Defined Networking (SDN) and Network-Function Virtualization (NFV). Additionally, we demonstrate how SDN-based networks can be modeled using DNI and how are they transformed later into Queueing Petri Nets (QPN) using a model-to-model transformation. In the analysis of the performance prediction accuracy, we show that automatically generated QPN models represent the performance of heterogeneous SDN hardware with maximal prediction accuracy error of 12 percent.}

@inproceedings{RySiSiAschKoSch2016-dni-traffic-extraction-icpe2016,
author = {Piotr Rygielski and Viliam Simko and Felix Sittner and Doris Aschenbrenner and Samuel Kounev and Klaus Schilling},
title = {{Automated Extraction of Network Traffic Models Suitable for Performance Simulation}},
year = {2016},
month = {March},
day = {12--18},
pages = {27--35},
doi = {http://dx.doi.org/10.1145/2851553.2851570},
booktitle = {Proceedings of the 7th ACM/SPEC International Conference on Performance Engineering (ICPE 2016)},
location = {Delft, The Netherlands},
publisher = {ACM},
abstract = {{Data centers are increasingly becoming larger and dynamic due to virtualization. In order to leverage the performance modeling and prediction techniques, such as Palladio Component Model or Descartes Modeling Language, in such a dynamic environments, it is necessary to automate the model extraction. Building and maintaining such models manually is not feasible anymore due to their size and the level of details. This paper is focused on traffic models that are an essential part of network infrastructure. Our goal is to decompose real traffic dumps into models suitable for performance prediction using Descartes Network Infrastructure modeling approach. The main challenge was to efficiently encode an arbitrary signal in the form of simple traffic generators while maintaining the shape of the original signal. We show that a typical 15 minute long tcpdump trace can be compressed to 0.4--15% of its original size whereas the relative median of extraction error is 0% for the most of the 69 examined traces.}},
note = {{Acceptance rate (Full Paper): 19/57 = 33\%}},
slides = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/slides/913},
pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/913.pdf},
url = {http://dl.acm.org/citation.cfm?doid=2851553.2851570}
}

@inproceedings{KoBrMeBeKoKoRy2016-SE-tradeoffs_perf_prediction_approaches,
author = {Samuel Kounev and Fabian Brosig and Philipp Meier and Steffen Becker and Anne Koziolek and Heiko Koziolek and Piotr Rygielski},
title = {{Analysis of the Trade-offs in Different Modeling Approaches for Performance Prediction of Software Systems}},
booktitle = {Software Engineering 2016 (SE 2016), Fachtagung des GI-Fachbereichs Softwaretechnik, 23.-26. M\"{a}rz 2016, Vienna, Austria},
publisher = {GI},
series = {Lecture Notes in Informatics (LNI)},
address = {Vienna, Austria},
days = {23-26},
month = {February},
year = {2016},
pages = {47--48},
titleaddon = {{(Talk Extended Abstract)}},
http = {http://subs.emis.de/LNI/Proceedings/Proceedings252/article3.html},
pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/1077.pdf},
slides = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/slides/1077}
}

@inproceedings{LaGeSpRyZiKoTG-SDN-Controller-Placement-ITC2015,
author = {Stanislav Lange and Steffen Gebert and Joachim Spoerhase and Piotr Rygielski and Thomas Zinner and Samuel Kounev and Phuoc Tran-Gia},
title = {{Specialized Heuristics for the Controller Placement Problem in Large Scale SDN Networks}},
booktitle = {27th International Teletraffic Congress ({ITC 2015})},
address = {Ghent, Belgium},
day = {8--10},
month = {September},
year = {2015},
pages = {210--218},
url = {http://dx.doi.org/10.1109/ITC.2015.32},
doi = {10.1109/ITC.2015.32},
abstract = {{The Software Defined Networking~(SDN) concept introduces a paradigm shift in the networking world towards an externalized control plane which is logically centralized. When designing an SDN-based WAN architecture, it is of vital importance to find a feasible solution to the controller placement problem, i.e., to decide where to position a limited amount of resources within the network. In addition to time-independent constraints regarding aspects like scalability, resilience, and control plane communication delays, dynamically changing network conditions like traffic patterns or bandwidth demands need to be considered as well. Consequently, such dynamic environments call for a regular and fast recalculation of placements in order to adapt to the current situation in a timely manner. While an exhaustive evaluation of all possible solutions can be performed within a practically feasible time frame for small and medium-sized networks, such an approach is out of scope for large problem instances which have significantly higher time and memory requirements. Therefore, this work investigates a specialized heuristic, which takes into account a particular set of optimization objectives and returns solutions representing the possible trade-offs between them. Due to its low computation time and acceptable margin of error, this heuristic can be employed by automatic decision systems operating in dynamic environments.}},
pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/803.pdf}
}

@inproceedings{RyKoTr2015-SIMUTools-FlexPerformancePrediction,
title = {{Flexible Performance Prediction of Data Center Networks using Automatically Generated Simulation Models}},
year = {2015},
month = {August},
days = {24--26},
pages = {119--128},
isbn = {978-1-63190-079-2},
doi = {10.4108/eai.24-8-2015.2260961},
location = {Athens, Greece},
booktitle = {Proceedings of the Eighth International Conference on Simulation Tools and Techniques (SIMUTools 2015)},
author = {Piotr Rygielski and Samuel Kounev and Phuoc Tran-Gia},
abstract = {{Using different modeling and simulation approaches for predicting network performance requires extensive experience and involves a number of time consuming manual steps regarding each of the modeling formalisms. In this paper, we propose a generic approach to modeling the performance of data center networks. The approach offers multiple performance models but requires to use only a single modeling language. We propose a two-step modeling methodology, in which a high-level descriptive model of the network is built in the first step, and in the second step model-to-model transformations are used to automatically transform the descriptive model to different network simulation models. We automatically generate three performance models defined at different levels of abstraction to analyze network throughput. By offering multiple simulation models in parallel, we provide flexibility in trading-off between the modeling accuracy and the simulation overhead. We analyze the simulation models by comparing the prediction accuracy with respect to the simulation duration. We observe, that in the investigated scenarios the solution duration of coarser simulation models is up to 300 times shorter, whereas the average prediction accuracy decreases only by 4 percent.}},
pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/789.pdf},
slides = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/slides/789}
}

@inproceedings{RyKo2014-DCPerf-DNI2QPN,
  author = {Piotr Rygielski and Samuel Kounev},
  booktitle = {34th IEEE International Conference on Distributed Computing Systems Workshops (ICDCS 2014 Workshops). 4th International Workshop on Data Center Performance, (DCPerf 2014)},
  location = {Madrid, Spain},
  title = {{Data Center Network Throughput Analysis using Queueing Petri Nets}},
  year = {2014},
  month = {June},
  day = {30},
  pages = {100--105},
  doi = {10.1109/ICDCSW.2014.11},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/705.pdf},
  abstract = {In this paper, we address the problem of performance analysis in computer networks. We present a metamodel designed for the performance modeling of network infrastructures in modern data centers. Instances of our metamodel can be automatically transformed into stochastic simulation models for performance prediction. In this paper, we present the transformation to Queueing Petri Nets (QPNs) and simulate them using SimQPN simulator. We show that despite the high level of abstraction of the QPNs, we are able to estimate the utilization of resources with good accuracy within a short time.},
}

In this paper, we address the problem of performance analysis in computer networks. We present a metamodel designed for the performance modeling of network infrastructures in modern data centers. Instances of our metamodel can be automatically transformed into stochastic simulation models for performance prediction. In this paper, we present the transformation to Queueing Petri Nets (QPNs) and simulate them using SimQPN simulator. We show that despite the high level of abstraction of the QPNs, we are able to estimate the utilization of resources with good accuracy within a short time.

@inproceedings{RyKoZs2013-ThroughputPrediction,
  author = {Piotr Rygielski and Samuel Kounev and Steffen Zschaler},
  booktitle = {{Proceedings of the 2nd IEEE International Workshop on Measurements and Networking (M\&N 2013)}},
  day = {7--8},
  location = {Naples, Italy},
  month = {October},
  pages = {167--172},
  isbn = {978-1-4673-2873-9},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/686.pdf},
  title = {{Model-Based Throughput Prediction in Data Center Networks}},
  year = {2013},
  abstract = {In this paper, we address the problem of performance analysis in computer networks. We present a new meta-model designed for the performance modeling of network infrastructures in modern data centers. Instances of our metamodel can be automatically transformed into stochastic simulation models for performance prediction. We evaluate the approach in a case study of a road traffic monitoring system. We compare the performance prediction results against the real system and a benchmark. The presented results show that our approach, despite of introducing many modeling abstractions, delivers predictions with errors less than 32% and correctly detects bottlenecks in the modeled network.},
}

In this paper, we address the problem of performance analysis in computer networks. We present a new meta-model designed for the performance modeling of network infrastructures in modern data centers. Instances of our metamodel can be automatically transformed into stochastic simulation models for performance prediction. We evaluate the approach in a case study of a road traffic monitoring system. We compare the performance prediction results against the real system and a benchmark. The presented results show that our approach, despite of introducing many modeling abstractions, delivers predictions with errors less than 32% and correctly detects bottlenecks in the modeled network.

@inproceedings{RyZsKo2013-DNI-meta-model,
  address = {New York, NY, USA},
  author = {Piotr Rygielski and Steffen Zschaler and Samuel Kounev},
  booktitle = {Proceedings of the 4th ACM/SPEC International Conference on Performance Engineering (ICPE 2013)},
  day = {21--24},
  location = {Prague, Czech Republic},
  month = {April},
  pages = {327--330},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/560.pdf},
  publisher = {ACM},
  title = {{A Meta-Model for Performance Modeling of Dynamic Virtualized Network Infrastructures}},
  titleaddon = {{(work-in-progress paper)}},
  url = {http://icpe2013.ipd.kit.edu/},
  year = {2013},
  abstract = {In this work-in-progress paper, we present a new meta-model designed for the performance modeling of dynamic data center network infrastructures. Our approach models characteristic aspects of Cloud data centers which were not crucial in classical data centers. We present our meta-model and demonstrate its use for performance modeling and analysis through an example, including a transformation into OMNeT++ for performance simulation.},
}

In this work-in-progress paper, we present a new meta-model designed for the performance modeling of dynamic data center network infrastructures. Our approach models characteristic aspects of Cloud data centers which were not crucial in classical data centers. We present our meta-model and demonstrate its use for performance modeling and analysis through an example, including a transformation into OMNeT++ for performance simulation.

@inproceedings{SwRy2011-CIST,
  author = {\'{S}wi\k{a}tek, Pawe{\l} and Rygielski, Piotr},
  booktitle = {{Proceedings of the VIth International Scientific and Technical Conference (CSIT 2011)}},
  day = {16--19},
  location = {Lviv, Ukraine},
  month = {November},
  pages = {136--139},
  publisher = {Publishing House Vezha&Co},
  title = {{Universal Comunication Platform for QoS-aware Delivery of Complex Services}},
  year = {2011},
}

@inproceedings{RySwJuGr2011-KES,
  address = {Berlin, Heidelberg},
  author = {Rygielski, Piotr and \'{S}wi\k{a}tek, Pawel and Juszczyszyn, Krzysztof and Grzech, Adam},
  booktitle = {Knowledge-Based and Intelligent Information and Engineering Systems, Part II (KES 2011)},
  day = {12--14},
  edition = {1},
  editor = {Koenig, A. and Dengel, A. and Hinkelmann, K. and Kise, K. and Howlett, R.J. and Jain, L.C.},
  isbn = {978-3-642-23862-8},
  location = {Kaiserslautern, Germany},
  month = {September},
  pages = {687--696},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/672.pdf},
  publisher = {Springer-Verlag},
  series = {{Lecture Notes in Computer Science (LNCS)}},
  title = {{Prediction Based Handovers for Wireless Networks Resources Management}},
  url = {http://dl.acm.org/citation.cfm?id=2041341.2041419},
  volume = {6882},
  year = {2011},
  abstract = {The paper is devoted to the problem of mobility and resources management in heterogeneous wireless networks. It is assumed that in certain area covered by multiple overlapping wireless networks there is certain number of mobile client which consume networks resources by use of available communication services (e.g., voice or data transmission) delivered by network providers. Moreover it is assumed, that communication services continuity may be assured with use of common handover techniques supporting clients mobility (e.g: MIPv6, IEEE 802.21, etc.). The task of mobility and resources management consists of making decisions concerning the moment and the network to which particular clients should be handed over in order to optimize certain quality criterion (e.g. utilization of network resources). In this paper we show that gathering knowledge about clients movement and prediction of their future position may significantly improve the overall quality of delivered services and network resources utilization.},
}

The paper is devoted to the problem of mobility and resources management in heterogeneous wireless networks. It is assumed that in certain area covered by multiple overlapping wireless networks there is certain number of mobile client which consume networks resources by use of available communication services (e.g., voice or data transmission) delivered by network providers. Moreover it is assumed, that communication services continuity may be assured with use of common handover techniques supporting clients mobility (e.g: MIPv6, IEEE 802.21, etc.). The task of mobility and resources management consists of making decisions concerning the moment and the network to which particular clients should be handed over in order to optimize certain quality criterion (e.g. utilization of network resources). In this paper we show that gathering knowledge about clients movement and prediction of their future position may significantly improve the overall quality of delivered services and network resources utilization.

@inproceedings{RyTo2011-KES,
  address = {Berlin, Heidelberg},
  author = {Rygielski, Piotr and Tomczak, Jakub},
  booktitle = {Knowledge-Based and Intelligent Information and Engineering Systems, Part II (KES 2011)},
  day = {12--14},
  edition = {1},
  editor = {Koenig, A. and Dengel, A. and Hinkelmann, K. and Kise, K. and Howlett, R.J. and Jain, L.C.},
  isbn = {978-3-642-23862-8},
  location = {Kaiserslautern, Germany},
  month = {September},
  pages = {591--600},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/673.pdf},
  publisher = {Springer-Verlag},
  series = {{Lecture Notes in Computer Science (LNCS)}},
  title = {{Context Change Detection for Resource Allocation in Service-Oriented Systems}},
  volume = {6882},
  year = {2011},
  abstract = {In this paper, the problem of detecting the major changes in the stream of service requests is formulated. The change of stream component varies over time and depends on, e.g., a time of a day. The underlying cause of the change is called a context. Hence, at each moment there exists a probability distribution determining the probability of requesting the system service conditioned by the context. The aim is to find such a moment in which the distributions change. To solve that problem dissimilarity measures between two probability distributions are given. Nevertheless, detecting every change is not interesting but only long-lasting changes because of the costs of the service system resources reallocation. Therefore, in the proposed algorithm an issue of sensitivity to temporary changes detection is considered},
}

In this paper, the problem of detecting the major changes in the stream of service requests is formulated. The change of stream component varies over time and depends on, e.g., a time of a day. The underlying cause of the change is called a context. Hence, at each moment there exists a probability distribution determining the probability of requesting the system service conditioned by the context. The aim is to find such a moment in which the distributions change. To solve that problem dissimilarity measures between two probability distributions are given. Nevertheless, detecting every change is not interesting but only long-lasting changes because of the costs of the service system resources reallocation. Therefore, in the proposed algorithm an issue of sensitivity to temporary changes detection is considered

@inproceedings{RyGo2011-ICSEng,
  address = {Los Alamitos, California USA},
  author = {Piotr Rygielski and Adam Gonczarek},
  booktitle = {ICSEng 2011: Proceedings of the 21st international conference on Systems Engineering (ICSEng 2011)},
  day = {16--18},
  editor = {Henry Selvaraj and Dawid Zydek},
  location = {Las Vegas, Nevada, USA},
  month = {August},
  pages = {212--216},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/678.pdf},
  publisher = {IEEE Computer Society's Conference Publishing Services},
  title = {{Migration-aware Optimization of Virtualized Computational Resources Allocation in Complex Systems}},
  year = {2011},
  abstract = {In this paper a task of resources allocation in the complex system is considered. Novelty of the formulated task consists of assumption that the applications assigned with resources of one machine can be migrated to another machine during system lifetime. The formulated task has been solved using proposed heuristic optimization method. Due to non-convex set of valid solutions the optimization procedure has been decomposed into two stages and forms approach similar to the relax-and-round approach. Proposed decomposition approach facilitates fast algorithm convergence and guaranties that achieved solution satisfies assumed constraints},
}

In this paper a task of resources allocation in the complex system is considered. Novelty of the formulated task consists of assumption that the applications assigned with resources of one machine can be migrated to another machine during system lifetime. The formulated task has been solved using proposed heuristic optimization method. Due to non-convex set of valid solutions the optimization procedure has been decomposed into two stages and forms approach similar to the relax-and-round approach. Proposed decomposition approach facilitates fast algorithm convergence and guaranties that achieved solution satisfies assumed constraints

@incollection{GrSwRy2010-IFIP,
  address = {Boston},
  author = {Grzech, Adam and \'Swi\k{a}tek, Pawel and Rygielski, Piotr},
  booktitle = {Software Services for e-World},
  editor = {Cellary, Wojciech and Estevez, Elsa},
  isbn = {978-3-642-16282-4},
  month = {November},
  pages = {17--28},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/681.pdf},
  publisher = {Springer},
  series = {IFIP Advances in Information and Communication Technology},
  title = {{Dynamic Resources Allocation for Delivery of Personalized Services}},
  url = {http://dx.doi.org/10.1007/978-3-642-16283-1_6},
  volume = {341},
  year = {2010},
  abstract = {The aim of this paper is to introduce a problem of e-health services quality management. The process of delivering e-health services to users consists of two major tasks: service personalization and resources allocation. In this paper we introduce a use-cases of e-health system and distinguish services that can be offered. In order to satisfy user requirements one have to manage resources properly especially when communication conditions change (e.g. in an ambulance). An exemplary solution has been presented and conclusions for further work have been formulated.},
}

The aim of this paper is to introduce a problem of e-health services quality management. The process of delivering e-health services to users consists of two major tasks: service personalization and resources allocation. In this paper we introduce a use-cases of e-health system and distinguish services that can be offered. In order to satisfy user requirements one have to manage resources properly especially when communication conditions change (e.g. in an ambulance). An exemplary solution has been presented and conclusions for further work have been formulated.

@inproceedings{GrRy2010-KES,
  address = {Berlin, Heidelberg},
  author = {Grzech, Adam and Rygielski, Piotr},
  booktitle = {Proceedings of the 14th International Conference on Knowledge-based and Intelligent Information and Engineering Systems (KES 2010)},
  day = {8--10},
  editor = {Setchi, Rossitza and Jordanov, Ivan},
  isbn = {978-3-642-15389-1},
  location = {Cardiff, UK},
  month = {September},
  pages = {523--532},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/679.pdf},
  publisher = {Springer-Verlag},
  series = {Lecture Notes in Computer Science (LNCS)},
  title = {{Translations of Service Level Agreement in Systems Based on Service Oriented Architecture}},
  url = {http://dl.acm.org/citation.cfm?id=1885375.1885435},
  volume = {6277},
  year = {2010},
  abstract = {The gain of the paper is to introduce and to discuss a formal specification of computer system's Service Level Agreement (SLA) and its translation into structure of complex services (composed of atomic services) delivering required functionalities and non-functionalities in distributed environment. The SLA is composed of two parts specifying quantitative and qualitative requirements. The former requirements define structure of the adequate complex services as a directed graph, where potential parallelism of atomic services performance may be taken into account. The qualitative requirements are applied to select the optimal complex service realization scenario; it is based on assumption that various atomic services distinguished in the complex services structure are available in the environment in different versions and locations. Different versions of atomic services are delivering the required functionalities and satisfy non-functionalities at various levels. Various locations of atomic services means that the time and cost of atomic services delivery (communication and calculation) may vary. Proposed model of SLA translation into complex services causes that a scenario variants may be applied, among others, to calculate upper and lower complex services delivering times and to estimate validity of possible parallelism in complex services.},
}

The gain of the paper is to introduce and to discuss a formal specification of computer system's Service Level Agreement (SLA) and its translation into structure of complex services (composed of atomic services) delivering required functionalities and non-functionalities in distributed environment. The SLA is composed of two parts specifying quantitative and qualitative requirements. The former requirements define structure of the adequate complex services as a directed graph, where potential parallelism of atomic services performance may be taken into account. The qualitative requirements are applied to select the optimal complex service realization scenario; it is based on assumption that various atomic services distinguished in the complex services structure are available in the environment in different versions and locations. Different versions of atomic services are delivering the required functionalities and satisfy non-functionalities at various levels. Various locations of atomic services means that the time and cost of atomic services delivery (communication and calculation) may vary. Proposed model of SLA translation into complex services causes that a scenario variants may be applied, among others, to calculate upper and lower complex services delivering times and to estimate validity of possible parallelism in complex services.

@incollection{RyPs2010-ICSS-GF,
  address = {ul. Maszynowa 5/9, 02-392 Warszawa, Poland},
  author = {Piotr Rygielski and Pawe\l{} \'Swi\k{a}tek},
  booktitle = {Applications of Systems Science},
  editor = {Adam Grzech and Pawel \'Swi\k{a}tek and Krzysztof Brzostowski},
  month = {September},
  note = {Most Promising Student Paper Award},
  pages = {217--226},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/664.pdf},
  publisher = {Exit},
  title = {{Optimal Complex Services Composition in SOA Systems}},
  year = {2010},
  abstract = {One of the most important tasks in service oriented architecture paradigm based systems is the task of composition of the complex service. Aim of this paper is to focus on the very last phase of the composition process, where proper atomic service versions are picked to execute the whole complex service. An exact algorithm is proposed in this paper solving two tasks based on popular quality of service delivery approaches: best-effort and differentiated services. The procedure of graph reduction has been introduced to generate space of possible solutions in such way that decision is made in more efficient way. The graph-fold algorithm was tested in simulation environment where its performance was compared to five reference algorithms. Moreover ability to deliver quality at desired level has been tested.},
}

One of the most important tasks in service oriented architecture paradigm based systems is the task of composition of the complex service. Aim of this paper is to focus on the very last phase of the composition process, where proper atomic service versions are picked to execute the whole complex service. An exact algorithm is proposed in this paper solving two tasks based on popular quality of service delivery approaches: best-effort and differentiated services. The procedure of graph reduction has been introduced to generate space of possible solutions in such way that decision is made in more efficient way. The graph-fold algorithm was tested in simulation environment where its performance was compared to five reference algorithms. Moreover ability to deliver quality at desired level has been tested.

@incollection{RyPs2010-ICSS-handover,
  address = {ul. Maszynowa 5/9, 02-392 Warszawa, Poland},
  author = {Piotr Rygielski and Pawe\l{} \'Swi\k{a}tek},
  booktitle = {Applications of Systems Science},
  editor = {Adam Grzech and Pawel \'Swi\k{a}tek and Krzysztof Brzostowski},
  month = {September},
  pages = {227--236},
  publisher = {Exit},
  title = {{Wireless Network Management Through Network-Enforced Handover}},
  year = {2010},
}

@inproceedings{GrRySw2009-HETNETS-QoS,
  address = {Ba{l}tycka 5, 44-100 Gliwice, Poland},
  author = {Adam Grzech and Piotr Rygielski and Pawel \'Swi\k{a}tek},
  booktitle = {Performance modelling and evaluation of heterogeneous networks, 6th Working International Conference (HET-NETs 2010)},
  day = {14--16},
  editor = {Tadeusz Czach{\'o}rski},
  isbn = {978-83-926054-4-7},
  location = {Zakopane, Poland},
  month = {January},
  pages = {35--47},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/670.pdf},
  publisher = {Institute of Theoretical and Applied Informatics of the Polish Academy of Sciences},
  title = {{QoS-aware Infrastructure Resources Allocation in Systems Based on Service-Oriented Architecture Paradigm}},
  year = {2010},
  abstract = {In this paper the task of communication and computational resources allocation in systems based on SOA paradigm is considered. The task of resources allocation consists in assigning resources to each incoming service request in such a way, that required level of the quality of service is met. Complex services performance time in distributed environment is assumed as the quality of service measure. Models of the system and analysis of service response time presented in this paper allowed to formulate several tasks of resource allocation in terms of well known quality of service assurance models: best effort, IntServ and DiffServ. For each formulated task solution algorithms were proposed and their correctness was evaluated by means of simulation.},
}

In this paper the task of communication and computational resources allocation in systems based on SOA paradigm is considered. The task of resources allocation consists in assigning resources to each incoming service request in such a way, that required level of the quality of service is met. Complex services performance time in distributed environment is assumed as the quality of service measure. Models of the system and analysis of service response time presented in this paper allowed to formulate several tasks of resource allocation in terms of well known quality of service assurance models: best effort, IntServ and DiffServ. For each formulated task solution algorithms were proposed and their correctness was evaluated by means of simulation.

@inproceedings{GrRySw2009-HETNETS-sim,
  address = {Ba{l}tycka 5, 44-100 Gliwice, Poland},
  author = {Adam Grzech and Piotr Rygielski and Pawel \'Swi\k{a}tek},
  booktitle = {Performance modeling and evaluation of heterogeneous networks, 6th Working International Conference (HET-NETs 2010)},
  day = {14--16},
  editor = {Tadeusz Czach{\'o}rski},
  isbn = {978-83-926054-4-7},
  location = {Zakopane, Poland},
  month = {January},
  pages = {89--97},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/669.pdf},
  publisher = {Institute of Theoretical and Applied Informatics of the Polish Academy of Sciences},
  title = {{Simulation Environment for Delivering Quality of Service in Systems Based on Service-Oriented Architecture Paradigm}},
  year = {2010},
  abstract = {In this paper a model of complex service in service-oriented architecture (SOA) system is presented. A complex service is composed with a set of atomic services. Each atomic service is characterized with its own non-functional parameters what allows to formulate quality of service optimization tasks. A simulation environment has been developed to allow experiments execution to determine quality of service (QoS) of composed service.},
}

In this paper a model of complex service in service-oriented architecture (SOA) system is presented. A complex service is composed with a set of atomic services. Each atomic service is characterized with its own non-functional parameters what allows to formulate quality of service optimization tasks. A simulation environment has been developed to allow experiments execution to determine quality of service (QoS) of composed service.

@incollection{GrRySw2010-SOAbook,
  address = {Pozna{\'n}, Poland},
  author = {Adam Grzech and Piotr Rygielski and Pawel \'{S}wi\k{a}tek},
  booktitle = {SOA Infrastructure Tools: Concepts and Methods},
  editor = {Stanislaw Ambroszkiewicz and Jerzy Brzezi\'{n}ski and Wojciech Cellary and Adam Grzech and Krzysztof Zieli\"{n}ski},
  isbn = {978-83-7417-544-9},
  pages = {289--312},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/666.pdf},
  publisher = {Pozna{\'n} University of Economics Press},
  title = {{QoS-aware Complex Service Composition in SOA-based Systems}},
  year = {2010},
  abstract = {In this work, a method for the QoS-aware complex service composition in SOA-based systems is presented. The considered complex service composition process consists of three stages: complex service structure, scenario and plan composition. Complex service structure contains a set of required functionalities and precedence relations between them, and is derived directly from a service level agreement. Service scenario is derived from service structure by choosing the optimal (in the sense of certain quality criterion) order of execution of required functionalities. Finally, a service plan emerges from a scenario by choosing the best versions of atomic services for the delivery of required functionalities. For such distinguished composition process methods for complex service scenario and execution plan optimization are proposed. Optimization of a complex service scenario is based on the analysis of possible parallel executions of required functionalities. In order to deliver required level of the quality of service, well known QoS assurance models (i.e.: best effort, integrated services and differentiated services) are applied in the process of complex service execution plan optimization.},
}

In this work, a method for the QoS-aware complex service composition in SOA-based systems is presented. The considered complex service composition process consists of three stages: complex service structure, scenario and plan composition. Complex service structure contains a set of required functionalities and precedence relations between them, and is derived directly from a service level agreement. Service scenario is derived from service structure by choosing the optimal (in the sense of certain quality criterion) order of execution of required functionalities. Finally, a service plan emerges from a scenario by choosing the best versions of atomic services for the delivery of required functionalities. For such distinguished composition process methods for complex service scenario and execution plan optimization are proposed. Optimization of a complex service scenario is based on the analysis of possible parallel executions of required functionalities. In order to deliver required level of the quality of service, well known QoS assurance models (i.e.: best effort, integrated services and differentiated services) are applied in the process of complex service execution plan optimization.

@inproceedings{GrSwRy2009-ICSE,
  author = {Adam Grzech and Pawel \'Swi\k{a}tek and Piotr Rygielski},
  booktitle = {Proceedings of Twentieth International Conference on Systems Engineering, (ICSE 2009)},
  day = {8--10},
  editor = {Keith J. Burnham and Olivier C. L. Haas},
  location = {Coventry, UK},
  month = {September},
  pages = {181--184},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/667.pdf},
  publisher = {Coventry University Press},
  title = {{Twostage Packet Scheduling in the Network Node}},
  year = {2009},
  abstract = {In this paper the problem of two-stage packet scheduling on parallel processors is considered. It is assumed, that each processor schedules packets according to Weighted Round Robin (WRR) rule. In order to deliver required level of the quality of service (QoS) weights of local WRR algorithms are adapted such that QoS requirements are met for all distinguished traffic classes. Adaptation of WRR weights relies on the adaptation through identification (Bubnicki, 2005) methodology with the diagonal recurrent neural network (DRNN) applied as the model of QoS parameters. Simulation study of the performance of proposed scheduling methodology shows, that it can deliver better QoS guaranties and higher systems throughput than commonly used reference algorithms.},
}

In this paper the problem of two-stage packet scheduling on parallel processors is considered. It is assumed, that each processor schedules packets according to Weighted Round Robin (WRR) rule. In order to deliver required level of the quality of service (QoS) weights of local WRR algorithms are adapted such that QoS requirements are met for all distinguished traffic classes. Adaptation of WRR weights relies on the adaptation through identification (Bubnicki, 2005) methodology with the diagonal recurrent neural network (DRNN) applied as the model of QoS parameters. Simulation study of the performance of proposed scheduling methodology shows, that it can deliver better QoS guaranties and higher systems throughput than commonly used reference algorithms.

@inproceedings{GrSwRy2009-PTS,
  author = {Adam Grzech and Pawel \'Swi\k{a}tek and Piotr Rygielski},
  booktitle = {Proceedings of the 16th Polish Teletraffic Symposium (PTS 2009)},
  day = {24--25},
  isbn = {978-83-7283-317-4},
  location = {L{\'o}d{\'Z}, Poland},
  month = {September},
  note = {Young Author Best Paper Award},
  organization = {Technical University of \L{}{\'o}d{\'Z}},
  pages = {53--56},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/668.pdf},
  title = {{Improving QoS Guaranties via Adaptive Packet Scheduling}},
  year = {2009},
  abstract = {In this paper the problem of packet scheduling in the node of packet-switched computer communication network is considered. Packet scheduling in the network node is one of the crucial mechanisms essential for delivery of required level of quality of services (QoS). In order to satisfy QoS guaranties for each connection belonging to one of distinguished traffic classes, packet scheduling algorithm must make decisions basing on current state of the scheduling system (e.g. buffer lengths) and actual characteristics of the serviced traffic (e.g.: connections lengths, packet intensities within connections, etc.). Here we propose a new packet scheduling algorithm based on Weighted Round Robin (WRR), which weights are adapted according to changes of system and traffic characteristics. By means of computer simulation, on representative examples, we show, that utilization of additional knowledge in the process of packet scheduling may improve QoS guaranties for serviced traffic.},
}

In this paper the problem of packet scheduling in the node of packet-switched computer communication network is considered. Packet scheduling in the network node is one of the crucial mechanisms essential for delivery of required level of quality of services (QoS). In order to satisfy QoS guaranties for each connection belonging to one of distinguished traffic classes, packet scheduling algorithm must make decisions basing on current state of the scheduling system (e.g. buffer lengths) and actual characteristics of the serviced traffic (e.g.: connections lengths, packet intensities within connections, etc.). Here we propose a new packet scheduling algorithm based on Weighted Round Robin (WRR), which weights are adapted according to changes of system and traffic characteristics. By means of computer simulation, on representative examples, we show, that utilization of additional knowledge in the process of packet scheduling may improve QoS guaranties for serviced traffic.

@misc{SPEC-RG-NEWSLETTER-5,
author = {Samuel Kounev and Andre van Hoorn and Piotr Rygielski},
month = {March},
note = {Published by Standard Performance Evaluation Corporation (SPEC)},
title = {{SPEC Research Group Newsletter, vol. 2 no. 1}},
url = {http://research.spec.org/en/newsletter.html},
year = {2016},
pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/1086.pdf}
}

@misc{SPEC-RG-NEWSLETTER-4,
author = {Samuel Kounev and Kai Sachs and Piotr Rygielski},
month = {January},
note = {Published by Standard Performance Evaluation Corporation (SPEC)},
title = {{SPEC Research Group Newsletter, vol. 1 no. 4}},
url = {http://research.spec.org/en/newsletter.html},
year = {2015},
pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/781.pdf}
}

@misc{SPEC-RG-NEWSLETTER-3,
  author = {Samuel Kounev and Kai Sachs and Piotr Rygielski},
  month = {March},
  note = {Published by Standard Performance Evaluation Corporation (SPEC)},
  title = {{SPEC Research Group Newsletter, vol. 1 no. 3}},
  url = {http://research.spec.org/en/newsletter.html},
  year = {2014},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/709.pdf},
}

@misc{SPEC-RG-NEWSLETTER-2,
  author = {Samuel Kounev and Kai Sachs and Piotr Rygielski},
  month = {June},
  note = {Published by Standard Performance Evaluation Corporation (SPEC)},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/685.pdf},
  title = {{SPEC Research Group Newsletter, vol. 1 no. 2}},
  url = {http://research.spec.org/en/newsletter.html},
  year = {2013},
}

@misc{SPEC-RG-NEWSLETTER-1,
  author = {Samuel Kounev and Kai Sachs and Piotr Rygielski},
  month = {September},
  note = {Published by Standard Performance Evaluation Corporation (SPEC)},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/684.pdf},
  title = {{SPEC Research Group Newsletter, vol. 1 no. 1}},
  url = {http://research.spec.org/en/newsletter.html},
  year = {2012},
}

@techreport{RyKo-DNI-Manual-TR,
address = {Am Hubland, 97074 W\"{u}rzburg},
author = {Piotr Rygielski and Samuel Kounev},
institution = {Chair of Software Engineering, University of W\"{u}rzburg},
month = {September},
title = {{Descartes Network Infrastructures (DNI) Manual: Meta-models, Transformations, Examples}},
type = {{Technical Report v.0.3}},
year = {2014},
url = {http://se.informatik.uni-wuerzburg.de/staff/piotr_rygielski/dni_manual/},
pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/769.pdf},
abstract = {The goal of this document is to present the DNI Meta-Model, its instances, sub-meta-models, and model transformations in more details than in an usual conference or journal paper. We describe the meta-models and the transformations in details, give example of systems modeled using the meta-models, and present the transformations in a step-by-step manner.}
}

@techreport{MiIoKoSaRyDiCiRo2013-TechReport-CloudUsagePatterns,
  abstract = {{Cloud computing is becoming an increasingly lucrative branch of the existing information and communication technologies (ICT). Enabling a debate about cloud usage scenarios can help with attracting new customers, sharing best-practices, and designing new cloud services. In contrast to previous approaches, which have attempted mainly to formalize the common service delivery models (i.e., Infrastructure-as-a-Service, Platform-as-a-Service, and Software-as-a-Service), in this work, we propose a formalism for describing common cloud usage scenarios referred to as cloud usage patterns. Our formalism takes a structuralist approach allowing decomposition of a cloud usage scenario into elements corresponding to the common cloud service delivery models. Furthermore, our formalism considers several cloud usage patterns that have recently emerged, such as hybrid services and value chains in which mediators are involved, also referred to as value chains with mediators. We propose a simple yet expressive textual and visual language for our formalism, and we show how it can be used in practice for describing a variety of real-world cloud usage scenarios. The scenarios for which we demonstrate our formalism include resource provisioning of global providers of infrastructure and/or platform resources, online social networking services, user-data processing services, online customer and ticketing services, online asset management and banking applications, CRM (Customer Relationship Management) applications, and online social gaming applications.}},
  address = {{7001 Heritage Village Plaza Suite 225, Gainesville, VA 20155, USA}},
  author = {Aleksandar Milenkoski and Alexandru Iosup and Samuel Kounev and Kai Sachs and Piotr Rygielski and Jason Ding and Walfredo Cirne and Florian Rosenberg},
  institution = {SPEC Research Group - Cloud Working Group, Standard Performance Evaluation Corporation (SPEC)},
  month = {May},
  url = {http://research.spec.org/fileadmin/user_upload/documents/rg_cloud/endorsed_publications/SPEC-RG-2013-001_CloudUsagePatterns.pdf},
  title = {{Cloud Usage Patterns: A Formalism for Description of Cloud Usage Scenarios}},
  type = {{Technical Report SPEC-RG-2013-001 v.1.0.1}},
  year = {2013},
  pdf = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/paper/432.pdf},
}

{Cloud computing is becoming an increasingly lucrative branch of the existing information and communication technologies (ICT). Enabling a debate about cloud usage scenarios can help with attracting new customers, sharing best-practices, and designing new cloud services. In contrast to previous approaches, which have attempted mainly to formalize the common service delivery models (i.e., Infrastructure-as-a-Service, Platform-as-a-Service, and Software-as-a-Service), in this work, we propose a formalism for describing common cloud usage scenarios referred to as cloud usage patterns. Our formalism takes a structuralist approach allowing decomposition of a cloud usage scenario into elements corresponding to the common cloud service delivery models. Furthermore, our formalism considers several cloud usage patterns that have recently emerged, such as hybrid services and value chains in which mediators are involved, also referred to as value chains with mediators. We propose a simple yet expressive textual and visual language for our formalism, and we show how it can be used in practice for describing a variety of real-world cloud usage scenarios. The scenarios for which we demonstrate our formalism include resource provisioning of global providers of infrastructure and/or platform resources, online social networking services, user-data processing services, online customer and ticketing services, online asset management and banking applications, CRM (Customer Relationship Management) applications, and online social gaming applications.}

@mastersthesis{rygielski2009a,
  abstract = {In this thesis, the problem of controlling network traffic for guaranteeing demanded Quality of Service level was presented. An architecture for network node with parallel processing units was considered and exemplary problems of teletraffic control were formulated. The process of service is a multistage process. A simulation environment was designed and developed for the needs of quantitatively analysis of control algorithms placed on the node. There were load balancing and packet scheduling algorithms implemented. Exemplary simulations were run to present functionality of environment and the way, users should implement their own, new algorithms was presented. At the end, the work was summarised and the future work plans were presented.},
  address = {Wybrze{\.z}e Wyspia{\'n}skiego 27, 50-370 Wroclaw, Poland},
  author = {Piotr Rygielski},
  month = {July},
  note = {The work is written in Polish language.},
  school = {Wroclaw University of Technology},
  title = {{Software implementation of the simulation environment of the system for multistage parallel processing of teletraffic in the node of the packet-switched network for traffic control algorithms performance analysis purposes.}},
  year = {2009},
}

In this thesis, the problem of controlling network traffic for guaranteeing demanded Quality of Service level was presented. An architecture for network node with parallel processing units was considered and exemplary problems of teletraffic control were formulated. The process of service is a multistage process. A simulation environment was designed and developed for the needs of quantitatively analysis of control algorithms placed on the node. There were load balancing and packet scheduling algorithms implemented. Exemplary simulations were run to present functionality of environment and the way, users should implement their own, new algorithms was presented. At the end, the work was summarised and the future work plans were presented.

@misc{Talk-KoBrMeBeKoKoRy2016-SE-tradeoffs_perf_prediction_approaches,
address = {Vienna, Austria},
author = {Samuel Kounev and Fabian Brosig and Philipp Meier and Steffen Becker and Anne Koziolek and Heiko Koziolek and Piotr Rygielski},
howpublished = {Software Engineering 2016 (SE 2016), Fachtagung des GI-Fachbereichs Softwaretechnik, 23.-26. M\"{a}rz 2016, Vienna, Austria},
title = {{Analysis of the Trade-offs in Different Modeling Approaches for Performance Prediction of Software Systems}},
days = {23-26},
month = {February},
year = {2016},
slides = {http://se2.informatik.uni-wuerzburg.de/pa/publications/download/slides/1103}
}

@misc{talk-Rygielski-OEW2012,
author = {Piotr Rygielski},
title = {{Modeling Virtualized Cloud Data Center Networks: Do We need QoS in Networks?}},
howpublished = {Open Excellence Workshop (Invited Talk), Charles University in Prague, Czech Republic.},
days = {21},
month = {June},
year = {2012}
}