Michael Segal - Academia.edu (original) (raw)

Papers by Michael Segal

ACM Transactions on Sensor Networks, Apr 3, 2023

In this paper, we investigate the topic of designing a sensor network by simultaneously optimizin... more In this paper, we investigate the topic of designing a sensor network by simultaneously optimizing its data energy eiciency and latency. We propose to design a network structure based on the number of nearest neighbors of wireless nodes and provide an analytic bound for the network measurements such as energy consumption and hop-diameter. We also show how to obtain the tradeof between both criteria. To the best of our knowledge, no non-trivial sublogarithmic hop-diameter bound has been known before. Moreover, our structure is highly fault resilient. We also present simulation results to validate our claims. 1

Annals of Computer Science and Information Systems, 2019

Position papers comprise two categories of contributions-challenge papers and emerging research p... more Position papers comprise two categories of contributions-challenge papers and emerging research papers. Challenge papers propose and describe research challenges in theory or practice of computer science and information systems. Papers in this category are based on deep understanding of existing research or industrial problems. Based on such understanding and experience, they define new exciting research directions and show why these directions are crucial to the society at large. Emerging research papers present preliminary research results from work-in-progress based on sound scientific approach but presenting work not completely validated as yet. They describe precisely the research problem and its rationale. They also define the intended future work including the expected benefits from solution to the tackled problem. Subsequently, they may be more conceptual than experimental. FedCSIS 2019 was Chaired by prof. Bogdan Franczyk, while prof. Rainer Unland acted as the Chair of the Organizing Committee. This year, FedCSIS was organized by the Polish Information Processing Society (Mazovia Chapter

Computer Networks, 2015

We study the problem of data collection in Wireless Sensor Networks (WSN). A typical WSN is compo... more We study the problem of data collection in Wireless Sensor Networks (WSN). A typical WSN is composed of wireless sensor nodes that periodically sense data and forward it to the base station in a multi-hop fashion. We are interested in designing an efficient data collection tree routing, focusing on three optimization objectives: energy efficiency, transport capacity, and hop-diameter (delay). In this paper we develop single-and multi-hop data collection, which are based on the definition of node centrality: centroid nodes. We provide theoretical performance analysis for our approach, present its distributed implementation and discuss the different aspects of using it. Most of our results are for two-dimensional WSNs, however we also show that the centroid-based approach is asymptotically optimal in three-dimensional random node deployments. In addition, we present new construction for arbitrary network deployment based on central nodes selection. We also present extensive simulation results that support our theoretical findings.

Proceedings of the 2016 Federated Conference on Computer Science and Information Systems, 2016

Wireless Networks, 2015

Vehicular networks are used to coordinate actions among vehicles in traffic by the use of wireles... more Vehicular networks are used to coordinate actions among vehicles in traffic by the use of wireless transceivers (pairs of transmitters and receivers). Unfortunately, the wireless communication among vehicles is vulnerable to security threats that may lead to very serious safety hazards. In this work, we propose a viable solution for coping with Man-in-the-Middle attacks. Conventionally, Public Key Infrastructure (PKI) is utilized for a secure communication with the pre-certified public key. However, a secure vehicle-to-vehicle communication requires additional means of verification in order to avoid impersonation attacks. To the best of our knowledge, this is the first work that proposes to certify both the public key and out-of-band sense-able static

2014 IEEE 13th International Symposium on Network Computing and Applications, 2014

International Journal of Satellite Communications and Networking, 2007

This paper presents the main achievements of a project, focused on the design of an integrated sy... more This paper presents the main achievements of a project, focused on the design of an integrated system composed of a satellite segment and a MANET to provide telecommunication services in emergency scenarios, in terms of network design, focusing in particular on the development of the interface between the two systems and showing the results of field trials.

In this paper we propose a novel approach to identify anomalies in DNS traffic. The traffic time-... more In this paper we propose a novel approach to identify anomalies in DNS traffic. The traffic time-points data is transformed to a string, which is used by new fast appproximate string matching algorithm to detect anomalies. Our approach is generic in its nature and allows fast adaptation to different types of traffic. We evaluate the approach on a large public dataset of DNS traffic based on 10 days, discovering more than order of magnitude DNS attacks in comparison to auto-regression as a baseline. Moreover, the additional comparison has been made including other common regressors such as Linear Regression, Lasso, Random Forest and KNN, all of them showing the superiority of our approach.

A wireless sensor network consists from a collection of transceivers positioned in the plane. Eac... more A wireless sensor network consists from a collection of transceivers positioned in the plane. Each transceiver is equipped with a limited battery charge. The battery charge is reduced after each transmission, depending on the transmission distance. One of the major problems in wireless ad hoc network is designing a route network traffic algorithm that will maximize the lifetime of the network i.e., the number of successful transmissions. Our objective is to construct a broadcast routing tree rooted at the source node with the longest possible lifetime. We perform a simulative study of the problem and show an improvement to currently existing BIP algorithm [18].

Given a set P of points in the plane, a geometric minimum-diameter spanning tree (GMDST)of P is a... more Given a set P of points in the plane, a geometric minimum-diameter spanning tree (GMDST)of P is a spanning tree of P such that the longest path through the tree is minimized. Forseveral years, the best upper bound on the time to compute a GMDST was cubic with respect to the number of points in the input set. Recently, Timothy Chan introduced a sub-cubic timealgorithm. In this paper, we present an algorithm that generates a tree whose diameter is no more than (1 + ffl) times that of a GMDST, for any ffl> 0. Our algorithm reduces the problem toseveral grid-aligned versions of the problem and runs within time O(ffl-3 + n) and space O(n). 1 Introduction Given a set P of points in the plane, define the weight of an edge between two points of P as the Euclidean (L2) distance between the points. Compute a spanning tree of P such that the longest path through the tree between any two points is minimized. This tree is known as a geometric minimum diameter spanning tree (GMDST) of the poin...

Mobile ad hoc networks (MANETs) are characterized by their intrinsic capability to be set up with... more Mobile ad hoc networks (MANETs) are characterized by their intrinsic capability to be set up without needing any kind of infrastructure, allowing a high degree of flexibility both at technological level and at application and service level. For this reason they are particularly useful in environment where no fixed network infrastructure is available. For example, they are well suitable for emergency application, when fixed telecommunication infrastructures, whereas present, can be seriously damaged or destroyed. Satellite networks also work without terrestrial infrastructure, excluding one gateway localized inside the footprint, and are easy to be set up too. For the same reasons also satellites can be fruitfully be utilized in case of emergency. Nevertheless, these two technologies are not in competition, as they might appear, but absolutely complementary. In fact, ad hoc mobile networks are characterized by very small terminals, low consumption, limited capacity per user terminals...

In this paper we study the dynamic version of the covering problem motivated by the coverage of d... more In this paper we study the dynamic version of the covering problem motivated by the coverage of drones' swarm: Let S be a set of n non-negative weighted points in the plane representing users. Also, consider a set P of m disks that correspond to the covering radius of each drone. We want to place (and maintain) set P such that the sum of the weights of the points in S covered by disks from P is maximized. We present a data structure that maintains a small constant factor approximate solution efficiently, under insertions and deletions of points to/from S where each update operation can be performed O(log n) time.

Given a set P of points in the plane, a geometric minimum-diameter spanning tree (GMDST) of P is ... more Given a set P of points in the plane, a geometric minimum-diameter spanning tree (GMDST) of P is a spanning tree of P such that the longest path through the tree is minimized. In this paper, we present an approximation algorithm that generates a tree whose diameter is no more than (1 + � ) times that of a GMDST, for any �> 0. Our algorithm reduces the problem to several grid-aligned versions of the problem and runs within time O(� −3 + n) and space O(n) improving the result by Gudmundsson et al. [4].

ArXiv, 2019

In this paper we study the dynamic version of the covering problem motivated by the coverage of d... more In this paper we study the dynamic version of the covering problem motivated by the coverage of drones' swarm: Let SSS be a set of nnn non-negative weighted points in the plane representing users. Also, consider a set PPP of mmm disks that correspond to the covering radius of each drone. We want to place (and maintain) set PPP such that the sum of the weights of the points in SSS covered by disks from PPP is maximized. We present a data structure that maintains a small constant factor approximate solution efficiently, under insertions and deletions of points to/from SSS where each update operation can be performed O(logn)O(\log n)O(logn) time.

Perform. Evaluation, 2021

In this paper we present a novel algorithm and efficient data structure for anomaly detection bas... more In this paper we present a novel algorithm and efficient data structure for anomaly detection based on temporal data. Time-series data are represented by a sequence of symbolic time intervals, describing increasing and decreasing trends, in a compact way using gradient temporal abstraction technique. Then we identify unusual subsequences in the resulting sequence using dynamic data structure based on the geometric observations supporting polylogarithmic update and query times. Moreover, we introduce a new parameter to control the pairwise difference between the corresponding symbols in addition to a distance metric between the subsequences. Experimental results on a public DNS network traffic dataset show the superiority of our approach compared to the baselines.

Security, Privacy, and Anonymity in Computation, Communication, and Storage

In this paper we propose a novel approach to identify anomalies in DNS traffic. The traffic time-... more In this paper we propose a novel approach to identify anomalies in DNS traffic. The traffic time-points data is transformed to a string, which is used by new fast approximate string matching algorithm to detect anomalies. Our approach is generic in its nature and allows fast adaptation to different types of traffic. We evaluate the approach on a large public dataset of DNS traffic based on 10 days, discovering more than order of magnitude DNS attacks in comparison to auto-regression as a baseline. Moreover, the additional comparison has been made including other common regressors such as Linear Regression, Lasso, Random Forest and KNN, all of them showing the superiority of our approach.

Ad-hoc networks of sensor nodes are in general semi-permanently deployed. However, the topology o... more Ad-hoc networks of sensor nodes are in general semi-permanently deployed. However, the topology of such networks continuously changes over time, due to the power of some sensors wearing out, to new sensors being inserted into the network, or even due to designers moving sensors around during a network re-design phase (for example, in response to a change in the requirements of the network). In this paper, we address the problem of how to dynamically maintain two important measures on the quality of the coverage of a sensor network: We maintain a (1 + ǫ)-approximation on the best-case coverage distance and a ( √ 2 + ǫ)-approximation on the worst-case coverage distance of the network, for any fixed ǫ > 0. We assume that the ratio between upper and lower transmission power of sensors is bounded by a polynomial of n, where n is the number of sensors. Our algorithms have amortized or worst-case poly-logarithmic update costs when the motion of mobile sensors can be described as a low-d...

Swarm formation and swarm flocking may conflict each other. Without explicit communication, such ... more Swarm formation and swarm flocking may conflict each other. Without explicit communication, such conflicts may lead to undesired topological changes since there is no global signal that facilitates coordinated and safe switching from one behavior to the other. Moreover, without coordination signals multiple swarm members might simultaneously assume leadership, and their conflicting leading directions are likely to prevent successful flocking. To the best of our knowledge, we present the first set of swarm flocking algorithms that maintain connectivity while electing direction for flocking, under conditions of no communication. The algorithms allow spontaneous direction requests and support direction changes. 2012 Elsevier B.V. All rights reserved.

2017 15th International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt), 2017

In this paper, we study the problem of data gathering in ad-hoc sensor networks using a mobile en... more In this paper, we study the problem of data gathering in ad-hoc sensor networks using a mobile entity called mule. The mule traverses the children of failed sensors, to prevent loss of data. Our objective is to define the optimal communication tree and the mule's placement such that the mule's overall traveling distance is minimized. We explore this problem in several network topologies including: unit disc graph on a line (UDL), general unit disc graph (UDG), and a complete graph with failing probabilities on the nodes (CGFP). We provide an optimal solution for the UDL problem and two approximation algorithms for the UDG problem. For the CGFP problem we outline the two possible structures of an optimal solution and provide near optimal approximation algorithms.

ACM Transactions on Sensor Networks, Apr 3, 2023

In this paper, we investigate the topic of designing a sensor network by simultaneously optimizin... more In this paper, we investigate the topic of designing a sensor network by simultaneously optimizing its data energy eiciency and latency. We propose to design a network structure based on the number of nearest neighbors of wireless nodes and provide an analytic bound for the network measurements such as energy consumption and hop-diameter. We also show how to obtain the tradeof between both criteria. To the best of our knowledge, no non-trivial sublogarithmic hop-diameter bound has been known before. Moreover, our structure is highly fault resilient. We also present simulation results to validate our claims. 1

Annals of Computer Science and Information Systems, 2019

Position papers comprise two categories of contributions-challenge papers and emerging research p... more Position papers comprise two categories of contributions-challenge papers and emerging research papers. Challenge papers propose and describe research challenges in theory or practice of computer science and information systems. Papers in this category are based on deep understanding of existing research or industrial problems. Based on such understanding and experience, they define new exciting research directions and show why these directions are crucial to the society at large. Emerging research papers present preliminary research results from work-in-progress based on sound scientific approach but presenting work not completely validated as yet. They describe precisely the research problem and its rationale. They also define the intended future work including the expected benefits from solution to the tackled problem. Subsequently, they may be more conceptual than experimental. FedCSIS 2019 was Chaired by prof. Bogdan Franczyk, while prof. Rainer Unland acted as the Chair of the Organizing Committee. This year, FedCSIS was organized by the Polish Information Processing Society (Mazovia Chapter

Computer Networks, 2015

We study the problem of data collection in Wireless Sensor Networks (WSN). A typical WSN is compo... more We study the problem of data collection in Wireless Sensor Networks (WSN). A typical WSN is composed of wireless sensor nodes that periodically sense data and forward it to the base station in a multi-hop fashion. We are interested in designing an efficient data collection tree routing, focusing on three optimization objectives: energy efficiency, transport capacity, and hop-diameter (delay). In this paper we develop single-and multi-hop data collection, which are based on the definition of node centrality: centroid nodes. We provide theoretical performance analysis for our approach, present its distributed implementation and discuss the different aspects of using it. Most of our results are for two-dimensional WSNs, however we also show that the centroid-based approach is asymptotically optimal in three-dimensional random node deployments. In addition, we present new construction for arbitrary network deployment based on central nodes selection. We also present extensive simulation results that support our theoretical findings.

Proceedings of the 2016 Federated Conference on Computer Science and Information Systems, 2016

Wireless Networks, 2015

Vehicular networks are used to coordinate actions among vehicles in traffic by the use of wireles... more Vehicular networks are used to coordinate actions among vehicles in traffic by the use of wireless transceivers (pairs of transmitters and receivers). Unfortunately, the wireless communication among vehicles is vulnerable to security threats that may lead to very serious safety hazards. In this work, we propose a viable solution for coping with Man-in-the-Middle attacks. Conventionally, Public Key Infrastructure (PKI) is utilized for a secure communication with the pre-certified public key. However, a secure vehicle-to-vehicle communication requires additional means of verification in order to avoid impersonation attacks. To the best of our knowledge, this is the first work that proposes to certify both the public key and out-of-band sense-able static

2014 IEEE 13th International Symposium on Network Computing and Applications, 2014

International Journal of Satellite Communications and Networking, 2007

This paper presents the main achievements of a project, focused on the design of an integrated sy... more This paper presents the main achievements of a project, focused on the design of an integrated system composed of a satellite segment and a MANET to provide telecommunication services in emergency scenarios, in terms of network design, focusing in particular on the development of the interface between the two systems and showing the results of field trials.

In this paper we propose a novel approach to identify anomalies in DNS traffic. The traffic time-... more In this paper we propose a novel approach to identify anomalies in DNS traffic. The traffic time-points data is transformed to a string, which is used by new fast appproximate string matching algorithm to detect anomalies. Our approach is generic in its nature and allows fast adaptation to different types of traffic. We evaluate the approach on a large public dataset of DNS traffic based on 10 days, discovering more than order of magnitude DNS attacks in comparison to auto-regression as a baseline. Moreover, the additional comparison has been made including other common regressors such as Linear Regression, Lasso, Random Forest and KNN, all of them showing the superiority of our approach.

A wireless sensor network consists from a collection of transceivers positioned in the plane. Eac... more A wireless sensor network consists from a collection of transceivers positioned in the plane. Each transceiver is equipped with a limited battery charge. The battery charge is reduced after each transmission, depending on the transmission distance. One of the major problems in wireless ad hoc network is designing a route network traffic algorithm that will maximize the lifetime of the network i.e., the number of successful transmissions. Our objective is to construct a broadcast routing tree rooted at the source node with the longest possible lifetime. We perform a simulative study of the problem and show an improvement to currently existing BIP algorithm [18].

Given a set P of points in the plane, a geometric minimum-diameter spanning tree (GMDST)of P is a... more Given a set P of points in the plane, a geometric minimum-diameter spanning tree (GMDST)of P is a spanning tree of P such that the longest path through the tree is minimized. Forseveral years, the best upper bound on the time to compute a GMDST was cubic with respect to the number of points in the input set. Recently, Timothy Chan introduced a sub-cubic timealgorithm. In this paper, we present an algorithm that generates a tree whose diameter is no more than (1 + ffl) times that of a GMDST, for any ffl> 0. Our algorithm reduces the problem toseveral grid-aligned versions of the problem and runs within time O(ffl-3 + n) and space O(n). 1 Introduction Given a set P of points in the plane, define the weight of an edge between two points of P as the Euclidean (L2) distance between the points. Compute a spanning tree of P such that the longest path through the tree between any two points is minimized. This tree is known as a geometric minimum diameter spanning tree (GMDST) of the poin...

Mobile ad hoc networks (MANETs) are characterized by their intrinsic capability to be set up with... more Mobile ad hoc networks (MANETs) are characterized by their intrinsic capability to be set up without needing any kind of infrastructure, allowing a high degree of flexibility both at technological level and at application and service level. For this reason they are particularly useful in environment where no fixed network infrastructure is available. For example, they are well suitable for emergency application, when fixed telecommunication infrastructures, whereas present, can be seriously damaged or destroyed. Satellite networks also work without terrestrial infrastructure, excluding one gateway localized inside the footprint, and are easy to be set up too. For the same reasons also satellites can be fruitfully be utilized in case of emergency. Nevertheless, these two technologies are not in competition, as they might appear, but absolutely complementary. In fact, ad hoc mobile networks are characterized by very small terminals, low consumption, limited capacity per user terminals...

In this paper we study the dynamic version of the covering problem motivated by the coverage of d... more In this paper we study the dynamic version of the covering problem motivated by the coverage of drones' swarm: Let S be a set of n non-negative weighted points in the plane representing users. Also, consider a set P of m disks that correspond to the covering radius of each drone. We want to place (and maintain) set P such that the sum of the weights of the points in S covered by disks from P is maximized. We present a data structure that maintains a small constant factor approximate solution efficiently, under insertions and deletions of points to/from S where each update operation can be performed O(log n) time.

Given a set P of points in the plane, a geometric minimum-diameter spanning tree (GMDST) of P is ... more Given a set P of points in the plane, a geometric minimum-diameter spanning tree (GMDST) of P is a spanning tree of P such that the longest path through the tree is minimized. In this paper, we present an approximation algorithm that generates a tree whose diameter is no more than (1 + � ) times that of a GMDST, for any �> 0. Our algorithm reduces the problem to several grid-aligned versions of the problem and runs within time O(� −3 + n) and space O(n) improving the result by Gudmundsson et al. [4].

ArXiv, 2019

In this paper we study the dynamic version of the covering problem motivated by the coverage of d... more In this paper we study the dynamic version of the covering problem motivated by the coverage of drones' swarm: Let SSS be a set of nnn non-negative weighted points in the plane representing users. Also, consider a set PPP of mmm disks that correspond to the covering radius of each drone. We want to place (and maintain) set PPP such that the sum of the weights of the points in SSS covered by disks from PPP is maximized. We present a data structure that maintains a small constant factor approximate solution efficiently, under insertions and deletions of points to/from SSS where each update operation can be performed O(logn)O(\log n)O(logn) time.

Perform. Evaluation, 2021

In this paper we present a novel algorithm and efficient data structure for anomaly detection bas... more In this paper we present a novel algorithm and efficient data structure for anomaly detection based on temporal data. Time-series data are represented by a sequence of symbolic time intervals, describing increasing and decreasing trends, in a compact way using gradient temporal abstraction technique. Then we identify unusual subsequences in the resulting sequence using dynamic data structure based on the geometric observations supporting polylogarithmic update and query times. Moreover, we introduce a new parameter to control the pairwise difference between the corresponding symbols in addition to a distance metric between the subsequences. Experimental results on a public DNS network traffic dataset show the superiority of our approach compared to the baselines.

Security, Privacy, and Anonymity in Computation, Communication, and Storage

In this paper we propose a novel approach to identify anomalies in DNS traffic. The traffic time-... more In this paper we propose a novel approach to identify anomalies in DNS traffic. The traffic time-points data is transformed to a string, which is used by new fast approximate string matching algorithm to detect anomalies. Our approach is generic in its nature and allows fast adaptation to different types of traffic. We evaluate the approach on a large public dataset of DNS traffic based on 10 days, discovering more than order of magnitude DNS attacks in comparison to auto-regression as a baseline. Moreover, the additional comparison has been made including other common regressors such as Linear Regression, Lasso, Random Forest and KNN, all of them showing the superiority of our approach.

Ad-hoc networks of sensor nodes are in general semi-permanently deployed. However, the topology o... more Ad-hoc networks of sensor nodes are in general semi-permanently deployed. However, the topology of such networks continuously changes over time, due to the power of some sensors wearing out, to new sensors being inserted into the network, or even due to designers moving sensors around during a network re-design phase (for example, in response to a change in the requirements of the network). In this paper, we address the problem of how to dynamically maintain two important measures on the quality of the coverage of a sensor network: We maintain a (1 + ǫ)-approximation on the best-case coverage distance and a ( √ 2 + ǫ)-approximation on the worst-case coverage distance of the network, for any fixed ǫ > 0. We assume that the ratio between upper and lower transmission power of sensors is bounded by a polynomial of n, where n is the number of sensors. Our algorithms have amortized or worst-case poly-logarithmic update costs when the motion of mobile sensors can be described as a low-d...

Swarm formation and swarm flocking may conflict each other. Without explicit communication, such ... more Swarm formation and swarm flocking may conflict each other. Without explicit communication, such conflicts may lead to undesired topological changes since there is no global signal that facilitates coordinated and safe switching from one behavior to the other. Moreover, without coordination signals multiple swarm members might simultaneously assume leadership, and their conflicting leading directions are likely to prevent successful flocking. To the best of our knowledge, we present the first set of swarm flocking algorithms that maintain connectivity while electing direction for flocking, under conditions of no communication. The algorithms allow spontaneous direction requests and support direction changes. 2012 Elsevier B.V. All rights reserved.

2017 15th International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt), 2017

In this paper, we study the problem of data gathering in ad-hoc sensor networks using a mobile en... more In this paper, we study the problem of data gathering in ad-hoc sensor networks using a mobile entity called mule. The mule traverses the children of failed sensors, to prevent loss of data. Our objective is to define the optimal communication tree and the mule's placement such that the mule's overall traveling distance is minimized. We explore this problem in several network topologies including: unit disc graph on a line (UDL), general unit disc graph (UDG), and a complete graph with failing probabilities on the nodes (CGFP). We provide an optimal solution for the UDL problem and two approximation algorithms for the UDG problem. For the CGFP problem we outline the two possible structures of an optimal solution and provide near optimal approximation algorithms.