Wyniki wyszukiwania - BazTech

1

Obowiązki komisów samochodowych

Walkowiak K.

Recykling

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2017

|

nr 1

67

PL

Temat obowiązków sprawozdawczych firm zajmujących się sprowadzaniem samochodów do Polski jest w ostatnim czasie bardzo popularny. A wszystko dzięki nowelizacji ustawy o recyklingu pojazdów wycofanych z eksploatacji. Każdy wprowadzający do 1000 pojazdów rocznie musi złożyć sprawozdanie dotyczące zapewnienia bądź niezapewnienia sieci zbierania pojazdów. Do przedkładania sprawozdań tego typu są również zobligowani więksi importerzy. Nie wszyscy importerzy mają świadomość obowiązku składania już od kilku lat także innych sprawozdań. Niestety, wiedza sprowadzających auta jest bardzo niewielka w tym zakresie, warto więc krótko przypomnieć ich podstawowe zobowiązania.

2

A column generation technique for routing and spectrum allocation in cloud-ready survivable elastic optical networks

Goścień R., Walkowiak K.

International Journal of Applied Mathematics and Computer Science

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2017

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Vol. 27, no. 3

591--603

EN

Driven by increasing user requirements and expectations, the fast development of telecommunications networks brings new challenging optimization problems. One of them is routing and spectrum allocation (RSA) of three types of network flows (unicast, anycast, multicast) in elastic optical networks (EONs) implementing dedicated path protection (DPP). In the paper, we model this problem as integer linear programming (ILP) and we introduce two new optimization approaches—a dedicated heuristic algorithm and a column generation (CG)-based method. Then, relying on extensive simulations, we compare algorithm performance with reference methods and evaluate CG efficiency in detail. The results show that the proposed CG method significantly outperforms reference algorithms and achieves results very close to optimal ones (the average distance to optimal results was at most 2.1%).

3

Szwedzki system recyklingu

Walkowiak K.

Recykling

|

2016

|

nr 2

62

4

Elastic optical networks - a new approach for effective provisioning of cloud computing and content-oriented services

Walkowiak K., Aibin M.

Przegląd Telekomunikacyjny + Wiadomości Telekomunikacyjne

|

2015

|

nr 8-9

691--697

EN

In this study, we combine cloud computing with a concept of EONs, which allows for efficient and scalable bandwidth provisioning. First, we outline the main features of EONs including issues like optical network evolution, architectures, distance adaptive transmission and survivability aspects. Next, we address topics related to dynamic routing in EONs with a special focus on traffic provisioned by data centers and present algorithms as well as results of simulations.

PL

Przedstawiono najważniejsze zagadnienia dotyczące zastosowania elastycznych sieci optycznych do realizacji usług sieciowych związanych z przetwarzaniem w chmurze oraz z dystrybucją treści, w tym omówiono ewolucję sieci optycznych, architektury sieci, transmisję dostosowującą się do odległości oraz przeżywalności sieci. Ponadto przedstawiono kwestie związane z dynamicznym zestawieniem połączeń w sieciach elastycznych wraz z przykładowymi wynikami symulacji komputerowych.

5

Podstawy teoretyczne samorządu zawodowego geodetów i kartografów

Walkowiak K.

Przegląd Geodezyjny

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2014

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R. 86, nr 11

8--10

6

Minimizing cost of network upgrade for overlay multicast – heuristic approach

Szostak M., Walkowiak K.

Journal of Telecommunications and Information Technology

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2013

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nr 3

66--73

EN

A rapid increase of the Internet users and traffic at the rate of 31% in years 2011–2016 contributes to emerging of new approaches to the content distribution. Among other approaches, the overlay multicasting seems to be one of the most interesting concepts according to relatively low deployment costs and large scalability. In this paper, the authors formulate a new incremental multicast overlay design problem. In particular, authors assumed that the overlay network is to be upgraded due to an increase of the number of participating users and the need to improve the streaming quality. However, the existing multicast tree structure is assumed to remain fixed. The goal was to minimize the cost of the upgrade, represented in euro/month. To achieve it, for each peer participating in the transmission, a link type offered by one of the ISPs was selected and overlay trees were constructed, rooted at the source of the content. The authors also present a new heuristic algorithm to efficiently solve this problem. According to experiments, the biggest factor influencing the upgrade cost and determining possible streaming quality values that the system can be upgraded to is the initial tree structure.

7

ILP modeling of many-to-many replicated multimedia communication

Walkowiak K., Bulira D., Careglio D.

Journal of Telecommunications and Information Technology

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2013

|

nr 3

56--65

EN

On-line communication services were evolving from a simple text-based chats towards sophisticated videopresence appliances. The bandwidth consumption of those services is constantly growing due to the technology development and high user and business needs. That fact leads us to implement optimization mechanisms into the multimedia communication scenarios. In this paper, the authors concentrate on many-to-many (m2m) communication, that is mainly driven by the growing popularity of on-line conferences and telepresence applications. An overlay model where m2m flows are optimally established on top of a given set of network routes is formulated and a joint model where the network routes and the m2m flows are jointly optimized. In the models, the traffic traverses through replica servers, that are responsible for stream aggregation and compression. Models for both predefined replica locations and optimized server settlement are presented. Each model is being followed by a comprehensive description and is based on real teleconference systems.

8

Optimization of overlay computing systems with many – to - many transmissions

Walkowiak K., Kasprzak A., Andrusieczko K.

Theoretical and Applied Informatics

|

2012

|

Vol. 24, No. 4

271-291

EN

The problem that this paper investigates, namely, optimization of overlay computing systems, follows naturally from growing need for effective processing and consequently, fast development of various distributed systems. We consider an overlay-based computing system, i.e., a virtual computing system is deployed on the top of an existing physical network (e.g., Internet) providing connectivity between computing nodes. The main motivation behind the overlay concept is simple provision of network functionalities (e.g., diversity, flexibility, manageability) in a relatively cost-effective way as well as regardless of physical and logical structure of underlying networks. The workflow of tasks processed in the computing system assumes that there are many sources of input data and many destinations of output data, i.e., many-to-many transmissions are used in the system. The addressed optimization problem is formulated in the form of an ILP (Integer Linear Programing) model. Since the model is computationally demanding and NPcomplete, besides the branch-and-bound algorithm included in the CPLEX solver, we propose additional cut inequalities. Moreover, we present and test two effective heuristic algorithms: tabu search and greedy. Both methods yield satisfactory results close to optimal.

PL

Zagadnienia dotyczące optymalizacji systemów obliczeń rozproszonych zyskują w ostatnich latach na znaczeniu. Systemy obliczeń rozproszonych rozwijane są w dwóch podstawowych architekturach sieciowych. Po pierwsze, budowane są dedykowane sieci optyczne łączące ośrodki obliczeniowe. Po drugie, wykorzystuje się istniejącą infrastrukturę sieciową (np. Internet) dla budowania systemów pracujących w architekturze nakładkowej (ang. overlay). Ta druga koncepcja zyskuje ostatnio dużą popularność, gdyż umożliwia szybką i tanią realizację systemów obliczeniowych bez potrzeby mocnej współpracy z operatorami sieciowymi. W pracy rozważamy nakładkowy system obliczeniowy umożliwiający transmisje wielu do wielu – dane wejściowe do obliczeń są generowane w wielu źródłach (węzłach sieciowych), następnie po przetworzeniu są przesyłane do wielu odbiorców zainteresowanych wynikami obliczeń. W oparciu o zaproponowaną architekturę systemu, w pracy sformułowano problem optymalizacyjny mający na celu minimalizację kosztów operacyjnych systemu obejmujących koszty obliczeń i koszty przesyłania danych. Model został zapisany jako program całkowitoliczbowy. Z uwagi na fakt, że ten problem należy do klasy problemów NP-zupełnych, zaproponowano dodatkowe odcięcia dla algorytmu podziału i oszacowań oraz dwa efektywne algorytmy heurystyczne. Przeprowadzone eksperymenty obliczeniowe wykazały, że opracowane algorytmy dają wyniki bliskie optymalnym w mniejszym czasie niż algorytm optymalny zawarty w pakiecie CPLEX

9

Heuristic algorithms for optimization of task allocation and result distribution in peer-to-peer computing systems

Chmaj G., Walkowiak K., Tarnawski M., Kucharzak M.

International Journal of Applied Mathematics and Computer Science

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2012

|

Vol. 22, no. 3

733-748

EN

Recently, distributed computing system have been gaining much attention due to a growing demand for various kinds of effective computations in both industry and academia. In this paper, we focus on Peer-to-Peer (P2P) computing systems, also called public-resource computing systems or global computing systems. P2P computing systems, contrary to grids, use personal computers and other relatively simple electronic equipment (e.g., the PlayStation console) to process sophisticated computational projects. A significant example of the P2P computing idea is the BOINC (Berkeley Open Infrastructure for Network Computing) project. To improve the performance of the computing system, we propose to use the P2P approach to distribute results of computational projects, i.e., results are transmitted in the system like in P2P file sharing systems (e.g., BitTorrent). In this work, we concentrate on offline optimization of the P2P computing system including two elements: scheduling of computations and data distribution. The objective is to minimize the system OPEX cost related to data processing and data transmission. We formulate an Integer Linear Problem (ILP) to model the system and apply this formulation to obtain optimal results using the CPLEX solver. Next, we propose two heuristic algorithms that provide results very close to an optimum and can be used for larger problem instances than those solvable by CPLEX or other ILP solvers.

10

Optimization of p2p-based distributed systems

Walkowiak K., Chmaj G., Kucharzak M., Siwek A., Skowron J.

Journal of Applied Computer Science

|

2011

|

Vol. 19, nr 1

117-138

EN

Various kinds of distributed systems gain much attention in recent years. One of the most significant example is the Peer-to-Peer (P2P) paradigm widely used in many applications including: file-sharing systems (e.g. BitTorrent), computing systems (e.g. SETI@home), communication systems (e.g. Skype) and many others. In this work we present our latest research related to the problem of P2P-based distributed systems optimization. We consider two following problems: optimization of data distribution P2P systems and optimization of P2P computing systems. For both problems we formulate Integer Programming models. Due to the complexity of these problems, exact methods can be applied only for relatively small instances. Therefore, we propose several heuristic algorithms including tabu search, evolutionary algorithm, constructive heuristic and random approach. Results of extensive numerical experiments show the effectiveness of proposed algorithms in comparison to optimal results yielded by CPLEX solver. The optimization methods presented in this paper can be used for optimization of various P2P systems.

11

Two Approaches to Network Design Problem for Overlay Multicast with Limited Tree Delay : Model and Optimal Results

Szostak M., Walkowiak K.

International Journal of Electronics and Telecommunications

|

2011

|

Vol. 57, No. 3

335-340

EN

Live multimedia streaming and on-demand streaming applications (such as Internet radio or Internet TV) have been gaining more popularity in recent years. They require significant amount of bandwidth from media streaming servers and can easily saturate network infrastructure when the number of participant or bit rate of streaming content increases. Overlay multicast is an effective approach to the problem of streaming distribution. It combines flexibility of application layer multicast with efficiency of network layer multicast. Since overlay networks are built on the top of existing infrastructure, the cost of maintenance and deployment of this solution is relatively low compared to traditional Content Distribution Networks (CDN). Based on our previous works, we focus on solving the overlay network design problem to economically distribute content among the participants using overlay multicast. The optimization goal is to minimize the overlay network cost expressed by the cost of access links. Additionally, we assume that the maximum total delay of a streaming tree is upper bounded to provide QoS (Quality of Service) guarantees. We present two approaches to this problem and construct model using Levels and Flow Conservation Constraints. We show how various constraints following from real overlay systems influence the behavior of the distributing system. In numerical experiments we use real ISPs' price lists. To illustrate our approach we present optimal results obtained from the CPLEX solver.

12

Modelling of Minimum Cost Overlay Multicast Tree in Two Layer Networks

Kucharzak M., Walkowiak K.

International Journal of Electronics and Telecommunications

|

2011

|

Vol. 57, No. 3

317-322

EN

Multicast realises the data delivering to a group of destinations simultaneously while using the minimum network resources. The first implementation of multicasting has been built using specialized multicast routers and is well known as IP Multicast. Such a network comprises some drawback including complex addressing and routing scheme, it requires the deployment of special routers that are rather expensive and finally, there has not been proposed a reasonable business model regarding cross-providers multicast realization. Thereby, for the past few years, a new interest in delivering multicast traffic has arisen and some multicast systems defined for end-hosts overlay network have been successfully proposed. Overlay multicast implements a multicast technique at the top of computer networks and creates a virtual topology of clients which duplicate packets and maintain a multicast structure. This overlay structure forms an independent layer with logical links between the nodes without the knowledge about the underlaying topology. In the work we take a look at flow cost minimization of multicast stream in a system which combines the advantages of overlays and underlaying network awareness. This papers presents three independent linear-based models aimed at optimization of multicast tree topology and its network level unicast realization. The proposed formulations can be applied for deriving either lower bound of flows costs in existing systems or for designing new cooperative multilayer protocols for effective multicast transmission.

13

A Lagrangean Relaxation Algorithm for Flow Optimization in Survivable MPLS Networks

Walkowiak K.

Theoretical and Applied Informatics

|

2010

|

Vol. 22, No. 1

19-47

EN

The problem that this paper investigates, namely, the working route assignment (WRA) problem, is one that arises naturally from problems of survivable network design that have recently received significant attention in data networking community. We consider an existing MPLS backbone transport network, which is in an operational phase and augmenting its resources is not possible. To address the issue of network survivability we apply restoration, i.e. after a network failure broken connections are dynamically restored. The main goal of our work is twofold. First, we want to develop an effective objective function for optimization of working routes in order to scale network flows and prepare the network for future failures and restoration. Second, we plan to find an efficient method to solve the WRA problem with this new objective function. Therefore, a function called RCL (Residual Capacity and Lost Flow in Link) facilitating the function LFL (Lost Flow in Link) developed previously by the author is formulated. Next, we present an approximation approach, called Lagrangean relaxation with heuristics (LRH) aimed to solve WRA with RCL as objective function. We further draw comparisons between LRH and an existing heuristic based on Flow Deviation algorithm. We also examine the performance of RCL against other functions in the context of network survivability. The results of simulation tests demonstrate that the new algorithm provides sub-optimal results, which are significantly better than other heuristic and the new function RCL can be effectively applied for assignment of working routes in survivable MPLS networks.

14

Trąba powietrzna na Opolszczyźnie - skutki, oszacowanie jej prędkości, klasyfikacja uszkodzeń budynków i ich odbudowa

Chmielewski T., Nowak H., Walkowiak K.

Inżynieria i Budownictwo

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2010

|

R. 66, nr 10

526-529

PL

Przedstawiono opis i klasyfikację uszkodzeń i zniszczeń budynków mieszkalnych, gospodarczych i użyteczności publicznej po przejściu trąby powietrznej 15 sierpnia 2008 r. Oszacowano prędkość wiatru trąby, omówiono proces odbudowy uszkodzonych budynków i podano propozycję rozwiązań technicznych zmniejszających skutki działania silnych wiatrów.

EN

Tornado near Opole passed over the area of six villages in the early evening of Friday 15th August 2008 and caused severe damage to buildings and infrastructure. An assessment of buildings performance and the engineering estimates of wind velocity were conducted in that case for the first time in Poland. The paper ends with recommendations for design and construction of buildings against very strong winds.

15

Tabu Search Algorithm for Survivable Network Design Problem with Simultaneous Unicast and Anycast Flows

Gładysz J., Walkowiak K.

International Journal of Electronics and Telecommunications

|

2010

|

Vol. 56, No. 1

41-47

EN

In this work we focus on the problem of survivable network design for simultaneous unicast and anycast flows. This problem follows from the growing popularity of network services applying the anycast paradigm. The anycasting is defined as one-to-one-of-many transmission and is applied in Domain Name Service (DNS), peer-to-peer (P2P) systems, Content Delivery Networks (CDN). In this work we formulate two models that enables joint optimization of network capacity, working and backup connections for both unicast and anycast flows. The goal is to minimize the network cost required to protect the network against failures using the single backup path approach. In the first model we consider modular link cost, in the second we are given a set of link proposal and we must select only one of them. Because these problems are NP-hard, therefore optimal solutions of branch-and-bounds or branch-and-cut methods can be generated for relatively small networks. Consequently, we propose a new heuristic algorithm based on Tabu Search method. We present results showing the effectiveness the proposed heuristic compared against optimal results. Moreover, we report results showing that the use of anycast paradigm can reduce the network cost.

16

Random Approach to Optimization of Overlay Public-Resource Computing Systems

Chmaj G., Walkowiak K.

International Journal of Electronics and Telecommunications

|

2010

|

Vol. 56, No. 1

55-61

EN

The growing need for computationally demanding systems triggers the development of various network-oriented computing systems organized in a distributed manner. In this work we concentrate on one kind of such systems, i.e. public-resource computing systems. The considered system works on the top of an overlay network and uses personal computers and other relatively simple electronic equipment instead of supercomputers. We assume that two kinds of network flows are used to distribute the data in the public-resource computing systems: unicast and peer-to-peer. We formulate an optimization model of the system. After that we propose random algorithms that optimize jointly the allocation of computational tasks and the distribution of the output data. To evaluate the algorithms we run numerical experiments and present results showing the comparison of the random approach against optimal solutions provided by the CPLEX solver.

17

Comparison of Evolutionary Algorithm and Heuristics for Flow Optimization in P2P Systems

Kucharzak M., Siwek A., Walkowiak K.

International Journal of Electronics and Telecommunications

|

2010

|

Vol. 56, No. 2

145-152

EN

Nowadays, many Internet users make use of Peer-to-Peer (P2P) systems to download electronic content including music, movies, software, etc. Growing popularity in P2P based protocol implementations for file sharing purposes caused that the P2P traffic exceeds Web traffic and in accordance with to many statistics, P2P systems produce a more than 50% of the whole Internet traffic. Therefore, P2P systems provide remarkable income for Internet Service Providers (ISP). However, at the same time P2P systems generates many problems related to traffic engineering, optimization, network congestion. In this paper we focus on the problem of flow optimization in P2P file sharing systems. Corresponding to BitTorrent-based systems behaviour, the optimization of P2P flows is very complex and in this work we consider different heuristic strategies for content distribution and moreover we propose a new evolutionary algorithm (EA) for this problem. We compare results of the algorithms against optimal results yielded by CPLEX solver for networks including 10 peers and relation to random algorithm for 100-node systems. According to numerical experiments, the EA provides solutions close to optimal for small instances and all of the heuristics exhibit a superior performance over random search.

18

Anycasting in connection-oriented computer networks: Models, algorithms and results

Walkowiak K.

International Journal of Applied Mathematics and Computer Science

|

2010

|

Vol. 20, no 1

207-220

EN

Our discussion in this article centers around various issues related to the use of anycasting in connection-oriented computer networks. Anycast is defined as a one-to-one-of-many transmission to deliver a packet to one of many hosts. Anycasting can be applied if the same content is replicated over many locations in the network. Examples of network techniques that apply anycasting are Content Delivery Networks (CDNs), Domain Name Service (DNS), Peer-to-Peer (P2P) systems. The role of anycasting is growing concurrently with the popularity of electronic music, movies, and other content required by Internet users. In this work we focus on the optimization of anycast flows in connection-oriented networks. We formulate a model of anycast connections and next propose a heuristic algorithm based on the Lagrangean relaxation aimed to optimize jointly routes for anycast and unicast connections. Results of numerical experiments are presented and evaluated. Finally, we analyze briefly problems related to anycasting in dynamic routing and multi-layer networks.

19

Branch-and-cut algorithm for optimization of non-bifurcated multicommodity flows in survivable networks

Walkowiak K.

Systems Science

|

2006

|

Vol. 32, no 3

27-35

EN

This paper addresses the problem of non-bifurcated multicommodity flow optimization in survivable networks. As the objective we apply the Lost Flow in Link (LFL) function, which is an upper bound of the flow that can be lost due to a failure of a single link. Since the problem under consideration is NP-complete we propose an exact algorithm to find optimal results. To facilitate the high computation complexity caused by the NP-completeness, we propose three cut inequalities: mixed integer rounding, cover inequality and upper bound on the objective function. Cuts are combined with the branch-and-bound algorithm to construct the branch-an-cut algorithm. We evaluate the proposed cuts by making numerical experiments using five network topologies with various demand patterns. Results of simulation prove the robustness of our approach - combined application of all three cuts reduces the number of nodes and decision time by 80% compared to the branch-and-bound algorithm.

20

Quasi-hierarchical evolution algorithm for flow assignment in survivable connection-oriented networks

Przewoźniczek M., Walkowiak K.

International Journal of Applied Mathematics and Computer Science

|

2006

|

Vol. 16, no 4

487-502

EN

The main objective of this paper is to develop an effective evolutionary algorithm (EA) for the path-assignment problem in survivable connection-oriented networks. We assume a single-link failure scenario, which is the most common and frequently reported failure event. Since the network flow is modeled as a non-bifurcated multicommodity flow, the discussed optimization problem is NP-complete. Thus, we develop an effective heuristic algorithm based on an evolutionary algorithm. The main novelty of this work is that the proposed evolutionary algorithm consists of two levels. The “high” level applies typical EA operators. The “low” level is based on the idea of a hierarchical algorithm. However, the presented approach is not a classical hierarchical algorithm. Therefore, we call the algorithm quasi-hierarchical. We present its description and the results of simulation runs over various networks.