Krzysztof Walkowiak

Krzysztof Walkowiak
Wroclaw University of Science and Technology | WUT · Department of Systems and Computer Networks

PhD

About

282
Publications
35,802
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
2,963
Citations
Additional affiliations
October 1997 - present
Wroclaw University of Science and Technology
Position
  • Professor (Associate)

Publications

Publications (282)
Conference Paper
The knowledge about future traffic volumes is beneficial for the network operators in many areas. Short-term forecasting of multiple traffic types helps with efficient resource utilization by enabling near real-time adjustment. An important issue is the choice of a suitable prediction model to obtain the most accurate traffic forecasts. A machine l...
Conference Paper
Full-text available
With the constant development of networking technologies and the increase of internet userbase, traffic prediction is becoming a vital part of today’s network optimization. In this paper, we propose a method for network traffic prediction based on the PROPHET model. We examine its different parameters find their best configuration for diverse traff...
Article
The latest trends in computer networks bring new challenges and complex optimization problems, one of which is link dimensioning in Spectrally-Spatially Flexible Optical Networks. The time-consuming calculations related to determining the objective function representing the amount of accepted traffic require heuristics to search for good quality so...
Article
In Elastic Optical Networks (EONs), the way different service demands are supported in the network is ruled by the Routing, Modulation and Spectrum Assignment (RMSA) algorithm, which decides how the spectrum resources of the optical network are assigned to each service demand. In a dynamic EON, demand requests arrive randomly one at a time and the...
Article
Full-text available
Rapid growth of network traffic causes the need for the development of new network technologies. Artificial intelligence provides suitable tools to improve currently used network optimization methods. In this paper, we propose a procedure for network traffic prediction. Based on optical networks’ (and other network technologies) characteristics, we...
Chapter
Prior knowledge regarding approximated future traffic requirements allows adjusting suitable network parameters to improve the network’s performance. To this end, various analyses and traffic prediction methods assisted with machine learning techniques are developed. In this paper, we study on-line multiple time series prediction for traffic of var...
Article
Full-text available
The rapid development of Cloud Computing and Content Delivery Networks (CDNs) brings a significant increase in data transfers that leads to new optimization challenges in inter-data center networks. In this article, we focus on the cross-stratum optimization of an inter-data center Elastic Optical Network (EON). We develop an optimization approach...
Article
Due to the continuous growth of Internet traffic, new technologies are proposed to overcome the capacity crunch problem. One of the most promising solutions for optical backbone networks is space division multiplexing (SDM), which allows parallel transmissions in properly designed optical fibers. In SDM, the problem of routing, space, and spectrum...
Article
Full-text available
Knowledge about future optical network traffic can be beneficial for network operators in terms of decreasing an operational cost due to efficient resource management. Machine Learning (ML) algorithms can be employed for forecasting traffic with high accuracy. In this paper we describe a methodology for predicting traffic in a dynamic optical netwo...
Chapter
Optical networks are vital communication infrastructure that supports services critical for the functioning of information society. The continuous growth of network traffic with tightening performance requirements combined with evolving physical-layer security threats poses multi-faceted challenges for network operators. To reduce network exposure...
Conference Paper
In this paper, we focus on the problem of resource allocation for time-varying traffic in translucent space-division multiplexing (SDM) elastic optical networks (EON) with back-to-back (B2B) signal regeneration. The performance is measured in terms of bandwidth blocking probability, usage of spectral resource (i.e. minimizing allocated bandwidth ov...
Chapter
The following paper considers pattern recognition-aided optimization of complex and relevant problem related to optical networks. For that problem, we propose a four-step dedicated optimization approach that makes use, among others, of a regression method. The main focus of that study is put on the construction of efficient regression model and its...
Conference Paper
In this paper, we motivate a brown-field migration planning as a cost-efficient procedure to scale the capacity of short-term realizable elastic optical networks (EONs), gradually converting them into spectrally-spatially flexible optical networks (SS-FONs). After a formal statement of the brown-field EON to SS-FON migration planning problem, a Sto...
Article
In this paper, we propose an optimization system based on an evolutionary algorithm developed to solve a real-life optimization problem related to the optimization of the computer networks. In particular, we focus on an NP-hard flow allocation problem in computer networks related to network survivability and addressing various constraints specific...
Article
Full-text available
In this paper, we focus on dynamic lightpath provisioning in translucent spectrally spatially flexible optical networks (SS-FONs) created with a combination of both spectral (EON) and spatial (SDM) flexibility. We utilize the distance-adaptive transmission (DAT) in order to select a modulation for request and routing path in a flexible manner. More...
Article
Full-text available
We consider a dynamic lightpath provisioning problem in translucent spectrally–spatially flexible optical networks (SS-FONs) in which flexible signal regeneration is achieved with transponders operating in back-to-back (B2B) configurations. In the analyzed scenario, an important aspect that has a significant impact on the network performance is the...
Article
Spectrally/spatially flexible optical networks (SS-FONs) are a promising solution to future traffic requirements in optical backbone networks. SS-FONs exploit the spatial dimension to increase the network capacity, while preserving the resource management flexibility, as they still operate within a flex-grid composed of small frequency slots (slice...
Chapter
Spectrally-spatially flexible optical networks (SS-FONs) are proposed as a solution for future traffic requirements in optical backbone networks. As SS-FONs operate within flex-grid, the provisioning of lightpaths spanning multiple frequency slots results in spectrum fragmentation, especially in presence of dynamic traffic. Fragmentation, in turn,...
Article
We focus on optimization of dynamic spectrally-spatially flexible optical networks (SS-FONs), in which distance-adaptive, spectral super-channel (SCh) transmission is realized over weakly-coupled multi-core fibers (MCFs). In such networks, the inter-core crosstalk (XT) effect in MCFs impairs the quality of transmission (QoT) of optical signals, whi...
Conference Paper
Following work focuses on optimization of dynamic spectrally-spatially flexible optical networks aided using supervised learning methods. Such kind of networks have distance-adaptive, spectral super-channel transmission realized over weakly-coupled multi-core fibers. Article proposes employing a pattern recognition approach with the goal to estimat...
Article
This article identifies the unavoidably required upgrade of short-term realizable elastic optical networks (EONs) operating over single-mode fibers toward spectrally-spatially flexible optical networks (SS-FONs), exploiting spatial division multiplexing (SDM) technology in order to cope with the expected mid- and long-term future traffic forecasts....
Conference Paper
We focus on spectrally-spatially flexible optical networks and analyze benefits of adjusting the number of active spatial modes in network links using various metrics based on data analytics with the goal to maximize the served traffic.
Conference Paper
Optimization of lightpath provisioning in a spectrally-spatially flexible optical network (SS-FON) is challenging due to many difficult constraints that exist in optical networks and because of limited amounts of various transmission resources (such as spectrum, spatial modes, transceivers, regeneration points). Previously demonstrated approaches u...
Conference Paper
Knowledge about future traffic in a dynamic optical network can be used to improve various performance metrics, including network cost and to reduce complexity of solving network optimization problems. In this paper, we propose a machine learning approach of predicting demands in a dynamic optical network serving Virtual Network Function (VNF) chai...
Article
We focus on the routing, spatial mode, and spectrum allocation (RSSA) problem-a basic optimization problem in spectrally and spatially flexible optical networks (SS-FON). RSSA is a very challenging problem since it introduces a new dimension, related to the selection of spatial resources, to the already complex (NP-hard) routing and spectrum alloca...
Conference Paper
Spectrally-spatially flexible optical networks (SS-FONs) are proposed as a solution for future traffic requirements in optical backbone networks. As SS-FONs operate within flex-grid, the provisioning of light-paths spanning multiple frequency slots results in spectrum fragmentation, especially in presence of dynamic traffic. Fragmentation, in turn,...
Conference Paper
We study inter-core crosstalk (ICXT) impact on migration planning toward spectrally-spatially flexible optical networks considering 22-core multi-core fiber. Results reveal, 55-70% of links need to be upgraded when ICXT ranges from -68.2 to-43.4 dB/km.
Article
Due to variety of modern real-life tasks, where analyzed data is often not a static set, the data stream mining gained a substantial focus of machine learning community. Main property of such systems is the large amount of data arriving in a sequential manner, which creates an endless stream of objects. Taking into consideration the limited resourc...
Article
Evolutionary methods are well-known tools used for solving hard computational problems. In this paper, we consider k¬-Shortest Steiner Trees (kSST) problem appearing in a diverse set of domains, e.g., multicast tree construction in communication networks in general, and optical networks in particular. The kSST is relatively new and has not been wid...
Conference Paper
We focus on a migration planning from elastic to spectrally-spatially flexible optical networks by upgrading regular with SDM-capable ROADMs. Our most promising strategy reveals that by migrating 30% of the regular ROADMs a 2x carried traffic increase can be achieved.
Article
Full-text available
The volume of data traffic in backbone networks is increasing at a speed that exceeds the growth rates of capacities offered in currently used wavelength division multiplex-ing (WDM) networks. As a short term solution to the potential capacity crunch, the concept of flexible-grid elastic optical networks is nowadays implemented in many backbone net...
Conference Paper
Full-text available
In last few years, cloud computing and other services based on data centers have evolved from an emerging technology to a recognized approach that is gaining broad acceptance and deployment. Therefore, there is a significant need to provide efficient and reliable operation of inter-data center networks based on optical technologies. In this article...
Conference Paper
In this article, we address the problem of survivable routing in spectrally-spatially flexible optical networks (SS-FONs) with dedicated path protection (DPP). The considered SS-FON supports spectral super-channel transmissions, in which flexible signal regeneration is realized with transceivers operating in back-to-back (B2B) configurations. We pr...
Conference Paper
Full-text available
We focus on a crosstalk-aware lightpath planning problem in a spectrally and spatially flexible optical network (SS-FON) in which spectral super-channels (SChs) are carried over multi-core fibers (MCFs) and distance-adaptive transmission is considered. The problem concerns establishing lightpath connections for a set of traffic demands in such a wa...
Conference Paper
In this paper, we consider spectrally-spatially flexible optical networks (SS-FONs) that combine the concept of space division multiplexing (SDM) and flexible-grid spectrally-flexible (elastic) optical networks (EONs). We assume that SS-FON uses spectral super-channel transmission, in which flexible signal regeneration is realized with transceivers...
Conference Paper
One of the most promising fibers for spatial division multiplexing (SDM) is weakly-coupled multi-core fiber (MCF). Despite significant capacity increase, MCFs suffer from physical layer impairments due to inter-core crosstalk (XT), which is the amount of signal leaking from adjacent cores. In this work, we focus on the impact of worst-case XT of MC...
Conference Paper
Full-text available
Spectrally and spatially flexible optical networks (SS-FONs), which combine space division multiplexing (SDM) with flexible-grid elastic optical network (EON) technologies, bring additional complexity to network control due to the handling of a larger number of spatial modes in SDM than in conventional EONs. To effectively optimize such networks, i...
Article
We focus on dynamic lightpath provisioning in translucent spectrally spatially flexible optical networks (SS-FONs) operating with multi-core fibers and realizing spectral super-channel transmission, in which flexible signal regeneration achieved with transceivers operating in back-to-back (B2B) configurations and modulation conversion is allowed. F...
Conference Paper
We focus on translucent flexgrid optical networks with flexible back-to-back regeneration and analyze the impact of the number of available transceivers on network performance for several proposed transceiver location methods and dynamic routing algorithms.
Conference Paper
Full-text available
Space division multiplexing (SDM) is a promising optical network technology with the scaling potential to overcome the possible capacity crunch problem in backbone networks. SDM enables parallel transmission of several co-propagating spatial modes in suitably designed optical fibers, such as multi-core fibers (MCFs). The MCFs are prone to excessive...
Conference Paper
Full-text available
In this paper, we consider resource allocation in data networks and evaluate the performance of various approaches using the Cross-Stratum Optimization architecture for a provider-centric use case. We describe many approaches used to provision various requests related to a data center operations. We consider three simple approaches and compare them...
Conference Paper
In this paper, we focus on dynamic lightpath provisioning in translucent elastic optical networks (EONs) realizing super-channel transmission in which flexible signal regeneration achieved with transponders operating in back-to-back (B2B) configurations and modulation conversion is allowed. We study potential power consumption savings and performan...
Article
In this paper, we focus on the performance of a survivable flex-grid network with space division multiplexing (SDM). To provide network survivability, we use dedicated path protection (DPP) and shared backup path protection (SBPP). For both schemes, we consider also squeezed protection that allocates backup resources only for a part of the primary...
Article
Full-text available
Space division multiplexing (SDM) is a promising optical network solution with the scaling potential to overcome the possible capacity crunch problem in backbone networks. In SDM optical networks, optical signals are transmitted in parallel through spatial modes co-propagating in suitably designed optical fibers. The combination of SDM with wavelen...
Article
Full-text available
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)....
Conference Paper
We examine potential performance gains resulting from a flexible use of signal regeneration achieved by means of transceivers in back-to-back configurations and along with modulation conversion in translucent elastic optical networks (EONs) under dynamic routing.
Conference Paper
Full-text available
In this paper, we analyse the cost and performance of inter-data center elastic optical network using various data center types for the problem of cloud service requests provisioning. The simulations are performed from the perspective of the network operator that wants to establish clients traffic, by using its own optical network and the external...
Conference Paper
Flexible-grid elastic optical networks (EONs) are expected to substitute in near future fixed-grid wavelength division multiplexing (WDM) optical networks. The previous works that were focused on optimization of EONs take many different assumptions regarding the transmission reach of modulation formats (MFs). However, according to the best of our k...
Conference Paper
Space division multiplexing (SDM) seems to be a promising solution with the scaling potential to overcome the possible capacity crunch problem in optical backbone networks. The main goal of this paper is to provide a detailed analysis of three SDM scenarios, namely, SDM-Fixed, SDM-Single, and SDM-Flexible in terms of the spectrum usage and the wast...
Conference Paper
Space division multiplexing (SDM) is a promising solution with the scaling potential to overcome the possible capacity crunch problem in optical backbone networks. The key idea behind SDM is to exploit the spatial dimension to provide a~significant increase in the transmission system capacity. In SDM, optical signals are transmitted in parallel thr...
Conference Paper
Full-text available
Current research in Evolutionary Computation concentrates on proposing more and more sophisticated methods that are supposed to be more effective than their predecessors. New mechanisms, like linkage learning (LL) that improve the overall method effectiveness, are also proposed. These research directions are promising and lead to effectiveness incr...
Conference Paper
Due to recent developments in cloud computing and constantly increasing demand for high bitrate content, both overlay networks and multicasting providing new data-sensitive applications and services have been gaining more and more attention in the last years. In this paper, we assume that the overlay network is deployed to provide multicasting of s...
Conference Paper
Cloud computing is dominating Internet services and would continue to expand in the foreseeable future. It is very challenging for network operators to evolve their infrastructures to be more intelligent and agile in resource orchestration. Nowadays, the optical networks term denotes high-capacity telecommunications networks based on optical techno...
Article
Full-text available
Contemporary classification systems have to make a decision not only on the basis of the static data, but on the data in motion as well. Objects being recognized may arrive continuously to a classifier in the form of data stream. Usually, we would like to start exploitation of the classifier as soon as possible, the models which can improve their m...
Conference Paper
The impact of modulation formats transmission reach on the spectrum usage in Elastic Optical Networks is studied. Results of extensive simulations run on representative network topologies are presented and discussed.
Article
We study potential performance gains resulting from deliberate use of signal regeneration along with modulation and spectrum conversion in translucent elastic optical networks (EONs) realizing super-channel transmission. We analyze three alternative scenarios that differ in the way in which translucent lightpath connections are provisioned. Namely,...
Conference Paper
Due to continuously increasing popularity of various network services the overall Internet traffic grows quickly. According to the recent Visual Networking Index report published by Cisco, the IP traffic will grow at a compound annual growth rate (CAGR) of 22 percent from 2015 to 2020. Space division multiplexing (SDM) in optical networks seems to...
Conference Paper
For the contemporary enterprises, possibility of appropriate business decision making on the basis of the knowledge hidden in stored data is the critical success factor. Therefore, the decision support software should take into consideration that data usually comes continuously in the form of so-called data stream, but most of the traditional data...
Conference Paper
Full-text available
Growing popularity of content-oriented services is a significant trend observed recently in communication networks. Due to large volumes of traffic related to these services, the network operators search for new solutions that allow to deliver content to end users in a cost-effective manner. Elastic optical network (EON) is a relatively novel solut...
Conference Paper
Full-text available
The ongoing transition towards a networked society requires reliable and secure network infrastructure and services. As networks evolve from simple point to point systems towards complex, software-defined, ultra-high capacity and reach, and distributed cloud environments, new security challenges emerge. The EU-funded RECODIS project aims at coordin...
Conference Paper
In this paper, we focus on the routing and spectrum allocation (RSA) problem in survivable elastic optical networks (EONs) with unicast and anycast traffic demands. We study a number of problem versions which differ in the involved technological constraints and facilities entailed by the EON technology, as well as, in the applied protection scheme,...
Conference Paper
Elastic Optical Network (EON) architecture has been proposed as a promising technology for a new generation of OFDM networks. It is based on the concept that spectrum can be split into smaller slices than are used currently in the fixed-grid network. It allows better spectral utilization and support for bit rates over 100 Gb/s. EONs arise with the...
Article
you can download this paper using the following link (50 downloads are available) http://www.tandfonline.com/eprint/3SVz9xibkdcA3zv9eJnf/full The Electronic Health Record (EHR) groups all digital documents related to a given patient such as anamnesis, results of the laboratory tests, prescriptions, recorded medical signals as ECG or images, etc. D...
Conference Paper
Full-text available
Elastic optical network (EON) is a technology that supports high bit-rate traffic demands in more efficient way comparing to traditional wavelength division multiplexing (WDM) optical networks. To facilitate the process of large content delivery in EONs, multicasting and anycasting transmission techniques can be applied instead of a simple unicast...
Article
In this paper, we focus on the survivability of elastic optical networks (EONs) that jointly support two types of traffic demands: unicast and anycast. To provide network survivability, we apply multipath routing; i.e., we allow the splitting of a demand into a number of routing paths if the paths' combination guarantees the realization of a specif...
Article
In this paper, an optimization problem in elastic optical networks (EONs) is considered. The problem concerns routing and spectrum allocation with joint optimization of anycast and unicast demands protected by dedicated optical paths. A new integer linear programming (ILP) problem formulation is presented, which aims at overcoming scalability probl...
Article
In this paper, we focus on the problem of locating data centers (DCs) and routing traffic demands in survivable elastic optical network (EON). We consider and compare two different modeling and optimization approaches: joint optimization of both issues at the same time (problem DC-RSA) and decomposition method, which divides problem into two subseq...
Conference Paper
Full-text available
The seemingly insatiable demand for mobile, video and cloud-based services shows no sign of slowing down. High bandwidth-consuming applications such as super-sized cloud storage and 4K/Ultra High Definition video services are becoming more and more popular. This causes requirements for optical networks to reach transmission of 100 Gbps and beyond....
Article
We present an optimization procedure that mixes advanced large-scale optimization methods and heuristics to solve large instances (with over 1.7 million integer variables) of the routing and spectrum allocation (RSA) problem - a basic optimization problem in flexgrid elastic optical networks. We formulate the problem as a mixed-integer program for...
Conference Paper
This work reports the research on active learning approach applied to the data stream classification. The chosen characteristics of the proposed frameworks were evaluated on the basis of the wide range of computer experiments carried out on the three benchmark data streams. Obtained results confirmed the usability of proposed method to the data str...
Data
Full-text available
Article
Presents key events and topics in the global communications industry.