Károly Farkas

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Papers by Károly Farkas

Specification of Network Services and Mapping Algorithms

In recent year, the functionality of networking infrastructure has expanded to the point where ro... more In recent year, the functionality of networking infrastructure has expanded to the point where routers not only provide data connectivity but also a variety of processing services. A major challenge in this context is to manage these processing resources and to allocate them to data transfers in an efficient manner. In our work 1 , we present a novel way of how endsystem applications can specify resource requirements. We explore the performance of several heuristic approaches to solving the intractable problem of mapping requirements to system resources.

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Introduction to WLAN IEEE802.11 Communication on Mobile Devices

John Wiley & Sons, Ltd eBooks, Jun 15, 2009

... Mobile Peer to Peer (P2P): A Tutorial Guide Edited by Frank HP Fitzek and Hassan Charaf © 200... more

Efficient event detection in public transport tracking

Personal mobile devices are widespread and carried by their users most of the time over the day. ... more Personal mobile devices are widespread and carried by their users most of the time over the day. Thanks to the integrated sensors they can report about visited places, movement types and speed of the users. However, efficient stopping event detection on public transport vehicles is still a challenge. These events, associated with the coordinates of real stations, can be useful to update public transit timetables according to real-time traffic. In field tests we evaluated the most commonly available suitable sensors' precision and efficiency and developed our Stopping Event Detection Algorithm (SEDA), which utilizes only the accelerometer to find potential stopping times and the Wi-Fi sensor to validate or discard them by a novel localization method. Wi-Fi is used only 6.66% of the time of actual traveling on public vehicles. Our algorithm is shown to recognize properly 82.9-89.47% of public traffic stations while consuming daily only 13% the capacity of an average smartphone's battery.

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Modeling Self-organized Application Spreading

Lecture Notes in Computer Science, 2011

General chairs message

AREP: an adaptive, machine learning-based algorithm for real-time anomaly detection on network telemetry data

Neural Computing and Applications, Nov 13, 2022

Abnormal behaviour detection is an essential task of real-time monitoring to secure the reliable ... more Abnormal behaviour detection is an essential task of real-time monitoring to secure the reliable operation of ICT infrastructures. This paper presents AREP, an adaptive, long short-term memory-based machine learning algorithm for real-time anomaly detection on network telemetry data. AREP is an improved version of Alter-Re 2 , the direct predecessor algorithm developed by our research team. AREP introduces automatic tuning of its two key parameters and includes an offset compensation component to increase accuracy. Unfortunately, AREP and its predecessors perform well only on time series showing specific patterns. Thus, we propose also a data type classification method to identify patterns on which AREP performs best. Moreover, we use an extended range of metrics in our performance evaluations, including area under the curve (AUC). AUC computation is based on receiver operating characteristic (ROC) curves. However, generating ROC curves is not straightforward due to the inherent adaptive threshold technique used by AREP and its predecessors, so we had to develop a novel ROC curve generation approach for these algorithms. We show through rigorous experiments that on network time series following specific data patterns AREP overperforms its predecessors and produces similar or even better performance than other state-of-the-art algorithms.

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A Publish-Subscribe Scheme Based Open Architecture for Crowd-Sourcing

Springer eBooks, 2013

Participatory sensing, when a crowd of users collaborate to collect useful information, based app... more Participatory sensing, when a crowd of users collaborate to collect useful information, based applications are getting popular these days thanks to the proliferation of powerful mobile devices. The builtin sensors of smartphones offer an easy and handy way to monitor the environment and collect data which can serve as the basis of smart applications. However, the quick and flexible development and deployment of these applications call for a unifying open architecture. In this paper we propose a publish-subscribe based open participatory sensing architecture.

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Advances in Wireless Mesh Networks

Mobile Networks and Applications, Apr 1, 2008

Wireless mesh networks facilitate the extension of wireless local area networks into wide areas a... more Wireless mesh networks facilitate the extension of wireless local area networks into wide areas and have emerged as a promising approach for future network accesses. Prior efforts on wireless networks, especially multi-hop ad hoc networks, have led to significant research contributions that range from fundamental results on theoretical capacity bounds to numerous practical routing and transport protocols. Unlike ad hoc networks, however, mesh networks can serve as access networks that employ multi-hop wireless forwarding by fixed mesh nodes to relay traffic to and from the wired Internet. The unique features of wireless mesh networks pose challenges in designing affordable, reliable, and sustainable network infrastructures. The critical issues span a rich spectrum of issues from interference-aware channel assignment, multi-hop routing, to reliable transport and infrastructure optimization, many of which have to be revisited in this new context. The purpose of this special issue is to archive the stateof-the-art achievements in wireless mesh networking. We received 30 original and unpublished research papers in both theoretical studies and practical protocol/architecture designs for wireless mesh networks, as well as prototypes. All these papers have gone through a strict peer review process, and among them, 14 high quality papers were selected, which offer a broad and updated coverage of wireless mesh network research and development. In addition, two high-quality papers selected from The Third International Wireless Internet Conference (WICON'2007) are included in this special issue as well. The first two papers of the special issue deal with quality of service (QoS) issue in wireless mesh networks. The paper "Provisioning of Parameterized Quality of Service in 802.11e Based Wireless Mesh Networks," by Xiaowen Chu, presents a framework for the provisioning of parameterized QoS in 802.11e based wireless mesh networks. By enforcing admission control algorithms and scheduling algorithms, this framework can support constant bit-rate (CBR) and variable bit-rate (VBR) traffic flows. Deterministic endto-end delay bounds for CBR traffic flows and VBR traffic flows that conform to leaky-bucket regulators have been derived. For VBR traffic flows without leaky-bucket regulators, a dynamic transmission opportunity (TXOP) scheduling algorithm has been proposed which was shown to be very effective in achieving high channel utilization ratio while keeping an acceptable delay performance. The paper entitled "QoS Differentiation for IEEE 802.16 WiMax Mesh Networks," by Yan Zhang, Honglin Hu, and Hsiao

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Simulation environment for investigating crowd-sensing based urban parking

This paper introduces a simulation environment developed for analyzing crowd-sensing based applic... more This paper introduces a simulation environment developed for analyzing crowd-sensing based applications in the Smart City application domain. As a case study, an urban parking application scenario is investigated and presented. In this scenario, smart citizens collect and share parking related events, such as leaving or occupying a free parking spot. These events can be presented on a real-time city map and used in navigation software, thereby helping others alleviate parking related issues, such as the time spent while cruising for parking. The simulation environment, implemented in Java, allows to investigate and assess the critical user base of crowd-sensing based smart city applications, and the requisites (benefits, challenges) of introducing such applications. Our simulation results show that considerable gain (approx. 15%) can be achieved in the cruising time even with relatively low (30%) user base in a medium size city (Novi Sad, Serbia). Moreover, the proposed simulation environment can be used also in real field measurements by replacing/extending input data from real users.

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Parking Assistance System for Indoor Environment

In the last decade, indoor location based applications, such as touristic guide in museums or sho... more In the last decade, indoor location based applications, such as touristic guide in museums or shopping guidance in supermarkets, have been developed rapidly requiring suitable and accurate indoor positioning. However, location sensing in indoor environments is a challenging task and an intensively researched topic. Fortunately, wireless technologies can help us derive location information. In this paper, we propose and introduce our positioning and navigation system for indoor parking garage environment, called iParking, which has been under development. The iParking system collects real-time parking lot occupancy data, and tracks and navigates vehicles entering the parking garage to a preselected, e.g., the closest to the favorite shop, free parking lot. The driver's smartphone is used as the navigation interface. The system is built on a background Wi-Fi infrastructure making the deployment and maintenance economical. Currently, we have been implementing a prototype of our iParking system in a parking garage of a shopping mall for demonstration purposes.

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Welcome and committees

On the Placement of Wi-Fi Access Points for Indoor Localization

Nowadays, the more and more popular location based applications require accurate position informa... more Nowadays, the more and more popular location based applications require accurate position information even in indoor environments. Wireless technologies can be used to derive positioning data. Especially, the Wi-Fi technology is popular for indoor localization because the existing and almost ubiquitous worldwide Wi-Fi infrastructure can be reused lowering the expenses. However, the primary purpose of these Wi-Fi systems is different from being used for positioning services, thus the accuracy they provide might be low. This accuracy can be increased by carefully placing the Wi-Fi access points to cover the given territory appropriately. In this paper, we propose a simulated annealing based method to find, in a given area, the optimal number and placement of Wi-Fi access points to be used for indoor positioning. We investigate the performance of our method via simulations.

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Supporting Distributed Services in Mobile Ad Hoc Networks

As mobile devices, such as laptops, PDAs or mobile phones, are getting more and more ubiquitous a... more As mobile devices, such as laptops, PDAs or mobile phones, are getting more and more ubiquitous and are able to directly communicate with each other via wireless technologies, the paradigm of wireless Mobile Ad hoc NRTworks (MANKTs) is gaining popularity. Especially distributed real-lime ap¬ plications, like rnultiplayer games, group-work or multimedia entertainment, are attractive for their users in this mobile ad hoc environment. However, MANtiTs impose new challenges because of their self-organizing, mobile and error-prone nature. Thus, provisioning distributed services in such an en¬ vironment is quite difficult. In this thesis, we focus on service management related issues and design, develop, implement and evaluate new mechanisms, which can aid the efficient creation of appropriate service management architecture for mobile ad hoc networks. Our contribution is threefold. First, we have designed and developed an algorithm called PBS (Priority Based Selection) to help manage distributed applications and support their smooth running in mobile ad hoc networks. PBS is based on graph theory and computes an appropriate Dominating Set (DS) of the network graph in a fully distributed manner applying node priority. The nodes in the DS then can be used as servers creating a robust, redundant client/server based service management architecture. Moreover, PBS is the first approach, according to our knowledge, in contrast to the existing DS computation algorithms that offers continuous maintenance of this set in dynamically changing network topologies, (t shows a stable performance even in case of high node mobility, keeping the DS computation time nearly constant. Second, we have designed and developed a mechanism called N WC (Node

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Evaluation of Simulation Engines for Crowdsensing Activities

Optimization of Wi-Fi Access Point Placement for Indoor Localization

The popularity of location based applications is undiminished today. They require accurate locati... more The popularity of location based applications is undiminished today. They require accurate location information which is a challenging issue in indoor environments. Wireless technologies can help derive indoor positioning data. Especially, the Wi-Fi technology is a promising candidate due to the existing and almost ubiquitous Wi-Fi infrastructure. The already deployed Wi-Fi devices can also serve as reference points for localization eliminating the cost of setting up a dedicated system. However, the primary purpose of these Wi-Fi systems is data communication and not providing location services. Thus their positioning accuracy might be insufficient. This accuracy can be increased by carefully placing the Wi-Fi access points to cover the given territory properly. In this paper, our contribution is a method based on simulated annealing, what we propose to find the optimal number and placement of Wi-Fi access points with regard to indoor positioning. We investigate its performance in a real environment scenario via simulations.

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Publish/Subscribe Communication for Crowd-sourcing Based Smart City Applications

Collecting data and monitoring our environment give the basis for smart city applications which a... more Collecting data and monitoring our environment give the basis for smart city applications which are getting popular today. However, the traditional approach to deploy a sensing and monitoring infrastructure is usually expensive and not always practical. Mobile crowd-sourcing can open new ways for data collection and smart city services. In this case, mobile devices with their built-in sensors and their owners are used to monitor the environment. For instance, the timetable of a smart travel planner service can be updated in real-time based on the continuously monitored time gap by passengers between consecutive buses on a public transportation route. This requires a common communication model facilitating crowd-sourced data collection. In this paper, we overview the design considerations of crowd-sourcing based smart city applications, propose data collection via using the publish/subscribe communication model and investigate the possible use of the Extensible Messaging and Presence Protocol (XMPP) for such applications.

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Performance evaluation of a live, crowdsensing based transit feed service architecture

Taking public transportation is an efficient and environmentally sound way of traveling in most o... more Taking public transportation is an efficient and environmentally sound way of traveling in most of the cities. Unfortunately, the static schedule information of the public transport vehicles, available at the stops, on the web or in some special format like GTFS (General Transit Feed Specification), usually does not reflect the actual traffic situation. However, realtime traffic updates require the gathering of an immense amount of tracking data. Mobile crowdsensing, via the mobile devices of the crowd, can offer a cheap and efficient way for collecting such data. Nonetheless, for motivating active participation some day zero service must be provided to the users. In this paper, we discuss how to realize a live public transport information service extending a static timetable based on GTFS data, as the day zero service, using the power of the crowd for data collection. We detail the design of such a service implemented by an XMPP (Extensible Messaging and Presence Protocol) based mobile crowdsensing architecture and evaluate its performance. We show how we can build a scalable service architecture even with commodity hardware to handle thousands of users.

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Managing Ubiquitous Communications and Services 2013

This volume presents the proceedings of the 10th International Workshop on Managing Ubiquitous Co... more This volume presents the proceedings of the 10th International Workshop on Managing Ubiquitous Communications and Services (MUCS 2013), which was held in San Diego, California, USA, March 18, 2013, as an integrated part of the 11th Annual IEEE International Conference on Pervasive Computing and Communications (PerCom 2013). As such, Ubiquitous Communications and Services, being part of pervasive computing and smart space applications, present a set of important management challenges for the successful delivery of highly adaptive services across heterogeneous networks, mobile networks, ad-hoc and sensor networks, middleware, applications, and devices. Such challenges include: managing user-centric services and context services, extreme distribution and scalability, extensive system and network and semantic heterogeneity, ad-hoc formation and disassociation of systems and services, and intelligent support for user centric applications. Today’s management systems need to keep pace with the complexity, heterogeneity, and automation required by the pervasive computing vision. The workshop in 2013 provides a single-track scientific program containing a blend of a keynote presentation, peer-reviewed papers, and a panel discussion addressing wireless and M2M communications and services for disaster management. While the goal of the workshop is to investigate the state of the art in managing pervasive/smart space applications from a broad perspective, the program reflects this goal in a coherent manner. The call for papers attracted 14 submissions, which have been received from authors in 9 different countries in Europe, Asia and North America, including one paper recommended from the PerCom main track. All submissions have been peer-reviewed, and 8 papers have been selected for full presentation at the workshop. The key topics in the workshop covered the areas of managing ubiquitous services and policies, context management and context-aware service management, managing smart spaces and environments, and infrastructure virtualization in next generation wireless sensor networks. These topics provide both a unique insight into the current state of the art in management of ubiquitous communications and services and suggest avenues for future research in this area. The keynote for MUCS 2013 was given by Prof. Mani Srivastava, University of California, Los Angeles, U.S.A. on a perfectly well fitting topic termed "Balancing Behavioral Privacy and Information Utility in Pervasive Sensing", which discussed the challenges inherent in designing a sensor information flow and processing architecture that is sensitive to the concerns of both producers and consumers. The team of General as well as TPC chairs would like to thank those researchers who submitted papers to the event, to the MUCS Technical Program Committee, for their advice and support through all the stages of the workshop preparation, the members of the PerCom 2013 conference organization committee, and to the sponsors giving financial support to running what we hope was a stimulating, rewarding and, most importantly, an enjoyable workshop for all its participants. March 2013 Dirk Pesch, Korbinian Frank, Karoly Farkas

The Dynamic Sensor Data Description and Data Format Conversion Language

Nowadays the proliferation of IoT (Internet of Things) devices results in heterogeneous and propr... more Nowadays the proliferation of IoT (Internet of Things) devices results in heterogeneous and proprietary sensor data formats which makes challenging the processing and interpretation of sensor data across IoT domains. To achieve syntactic interoperability (the ability to exchange uniformly structured data) is still an issue under research. In this paper, we introduce our purpose developed new script language called Language for Sensor Data Description (L4SDD) to achieve cross-domain syntactic interoperability. L4SDD defines a unified output data format and specifies how the data is to be converted into this format from the various sensor inputs. Besides the language itself, we also present the main features of the workbench created to edit and maintain the scripts and introduce the IoT framework around the solution. The approach provides a high performant, secure and easy-to-use solution to transform their data to an easily processed, self-describing, universal data structure. Although the paper contains implementation details, the solution can be used in other, similar projects as well. As a practical validation, we also illustrate our solution via a real-life case study.

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Planning of Wireless Community Networks

Advances in e-business research series, 2009

The objective of this chapter is to discuss the applications, state-of-the-art technologies, plan... more The objective of this chapter is to discuss the applications, state-of-the-art technologies, planning methods and business models for wireless community networks and provide an integrated presentation of these essential parts with examples. After a short introduction we give an overview about the state-of-the-affairs of wireless community networks presenting the driving forces, stakeholders, services and built upon applications in some carefully selected projects. Then, we discuss the technological aspects and suggest a design methodology for planning wireless community networks. The application of this methodology is illustrated via an ongoing digital city project in Hungary. After this we analyze the relevant business models and include a sample financial calculation. And finally, before concluding the chapter we give a short outlook discussing the future trends of the area.

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