Karol Kowalik

Dublin Institute of Technology, Dublin, Leinster, Ireland

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Publications (23)1.28 Total impact

  • Source
    Yin Chen, K. Kowalik, M. Davis
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    ABSTRACT: A core problem of fast handoff is when handoff should perform and which Mesh Node (MN) should associated with. We have developed a fast handoff management scheme called MeshScan to provide a novel use of channel scanning latency, by employing open system authentication in both Passive Handoff and Active Handoff. This scheme comprises three steps: firstly a client device takes advantage of the Wireless Mesh Network (WMN) architecture to maintain a list of active MNs. Secondly MeshScan Handoff Sensor performs handoff when it receives a disassociation management frame from the serving MN or when the measured signal strength from the serving MN exceeds a given threshold. Thirdly when handoff is required, a client transmits Authentication Request frames to all MNs from the list instead of broadcasting Probe Request frames, as in an active scan to discover the available MNs. The handoff delay is used as criteria for system performance. Numerical results are presented to demonstrate the feasibility of MeshScan with Active Handoff algorithm. This fast handoff scheme is feasible by upgrading the software only on the client side. This paper compares the theoretical handoff latency of MeshScan with other approaches and we demonstrate the effectiveness of our scheme through experiment.
    Wireless Communications & Signal Processing, 2009. WCSP 2009. International Conference on; 12/2009
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    Chenzhe Zhang, K. Kowalik, M. Davis
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    ABSTRACT: Next-generation wireless mobile communications will be driven by converged networks that integrate disparate technologies and services. Wireless Mesh Networks (WMNs) are expected to be one of the next generation of wireless interconnection technologies, providing flexible high bandwidth wireless backhaul over large geographical areas. While single radio mesh nodes operating on a single channel suffer from capacity constraints, equipping mesh routers with multiple radios using multiple non-overlapping channels can significantly alleviate the capacity problem and increase the aggregate bandwidth available to the network. However, it is well known that multi-radio Mesh platforms face many limitations such as interference, radiation leakage, crosstalk and limited computing resource etc. A misperception among researchers is that the so called "crosstalk" is one of the limiting factors to the performance decrease in multi-radio Mesh networks, but through a series of experiments the results shows otherwise. In this paper, we present a unique experimental approach that utilizes antenna cables, splitters, couplers and attenuators etc. to create a controlled wireless environment, and results indicates, despite negligible effect, crosstalk is not a limiting factor, but rather the finite computing resource constrains the aggregated performance of multi-radio Mesh networks, and several other factors have been investigated as well.
    Wireless Communications, Networking and Mobile Computing, 2009. WiCom '09. 5th International Conference on; 10/2009
  • Yin Chen, Karol Kowalik, Mark Davis
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    ABSTRACT: Handoff delay is one of the major problems in Wireless Mesh Network (WMN) that needs to be solved in order to allow time-critical and real-time applications run continuously during handoff. We have developed a fast handoff scheme called MeshScan to provide a novel use of channel scanning latency by employing open system authentication. This scheme comprises two steps: firstly a client device takes advantage of the WMN architecture to maintain a list of active mesh nodes. Secondly when handoff is required, a client transmits Authentication Request frames to all mesh nodes (MNs) from the list instead of broadcasting Probe Request frames as in an active scan to discover the available MNs. This fast handoff scheme is feasible by upgrading the software only on the client side. This paper compares the theoretical handoff latency of MeshScan with other approaches and we demonstrate the effectiveness of our scheme through experiment.
    Proceedings of the Seventh ACM International Workshop on Mobility Management & Wireless Access, MOBIWAC 2009, Tenerife, Canary Islands, Spain, October 26-27, 2009; 01/2009
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    ABSTRACT: Power control techniques for IEEE 802.11 wireless networks have already gained considerable attention. Such techniques are particularly attractive because they can improve various aspects of wireless network operation such as interference mitigation, spatial reuse in dense wireless deployments, topology control, and link quality enhancement. In this paper we propose a novel delivery ratio based Conservative Transmit Power Control (ConTPC) mechanism. Our implementation is conservative when it comes to deciding if the transmit power should be reduced for a given link. This is because we do not want poor quality wireless links to further reduce their quality and be overwhelmed by other links transmitting at maximum power. We have experimentally evaluated the benefit of the proposed power control scheme when compared with fixed power level systems. We show that our ConTPC mechanism can increase the throughput, however the magnitude of this enhancement largely depends on the topology of the wireless network.
    12/2008: pages 399-411;
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    ABSTRACT: Power control techniques for IEEE 802.11 wireless networks have already gained much attention. Such techniques are particularly attractive because they can improve various aspects of wireless network operation such as interference mitigation, spatial reuse in dense wireless deployments, topology control, and link quality enhancement. However, until recently implementing such advanced power control using off-the-shelf wireless devices was not considered possible. For example, Abdesslem et al. [1] stated that ldquomany novel power control solutions cannot be efficiently implemented over existing IEEE 802.11 cardsrdquo. However, in this paper we demonstrate that power control is now feasible and can be implemented in current IEEE 802.11 cards with per-packet granularity and low power switching latency.
    Telecommunications, 2008. ICT 2008. International Conference on; 07/2008
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    [Show abstract] [Hide abstract]
    ABSTRACT: Power control techniques for IEEE 802.11 wireless networks have already gained considerable attention. Such techniques are particularly attractive because they can improve various aspects of wireless network operation such as interference mitigation, spatial reuse in dense wireless deployme nts, topology control, and link quality enhancement. In this paper we propose a novel delivery ratio based Conservative Transmit Power Control (ConTPC) mechanism. Our implementation is conservative when it comes to deciding if the transmit power should be reduced for a given link. This is because we do not want poor quality wireless links to further reduce their quality and be overwhelmed by other links transmitting at maximum power. We have experi- mentally evaluated the benefit of the proposed power control scheme wh en compared with fixed power level systems. We show that our ConTPC mechanism can increase the throughput, however the magnitude of this enhancement largely depends on the topology of the wireless network.
    WINSYS 2008 - Proceedings of the International Conference on Wireless Information Networks and Systems, Porto, Portugal, July 26-29, 2008, WINSYS is part of ICETE - The International Joint Conference on e-Business and Telecommunications; 01/2008
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    B. Keegan, K. Kowalik, M. Davis
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    ABSTRACT: Wireless Mesh Networks (WMNs) represent the next generation wireless networks. The increased capacity of WMNs means that they are now capable of providing backhaul services traditionally maintained by wired networks. The attraction of WMNs is their ease of deployment and ability to self organise, self configure, and self heal. In order to successfully achieve this objective careful consideration must be applied when constructing a WMN. In order to optimise the operation of the network, data should traverse the network by means of the most efficient route. Characterisation and path selection will be determined by the routing algorithm coupled with the link cost metrics. In this paper we experimentally investigate the overhead associated with the estimation of the link quality using the Estimated Transmission Time (ETT) metric.
    Signal Processing and Communications, 2007. ICSPC 2007. IEEE International Conference on; 12/2007
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    Karol Kowalik, Brian Keegan, Mark Davis
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    ABSTRACT: An important element of any routing protocol used for Wireless Mesh Networks (WMNs) is the link cost function used to represent the radio link characteristic. The majority of the routing protocols for WMNs attempt to accurately characterise the radio link quality by constructing the link cost function from the measurements obtained using active probing techniques which introduces overhead. In this paper we present a modified version of the Optimized Link State Routing (OLSR) protocol which uses the link cost function values provided the Resource Aware Routing for mEsh (RARE) module which employs passive monitoring to gather radio link information. This results in a smaller overhead than the other methods that require active network probing and furthermore is load independent since it does not require an access to the medium. We demonstrate the necessary modifications to OLSR required to make it work with RARE. The results of our ns-2 simulations show that such a combination (OLSR + RARE) performs well over various wireless topologies.
    Wireless Communications, Networking and Mobile Computing, 2007. WiCom 2007. International Conference on; 10/2007
  • Source
    Karol Kowalik, Brian Keegan, Mark Davis
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    ABSTRACT: An important element of any routing protocol used for wireless mesh networks (WMNs) is the link cost function used to represent the radio link characteristic. The majority of the routing protocols for WMNs attempt to accurately characterise the radio link quality by constructing the link cost function from the measurements obtained using active probing techniques, which introduces overhead. In this paper we propose a new approach called resource aware routing for mesh (RARE) which instead employs passive monitoring to gather radio link information. This results in a smaller overhead than the other methods that require active network probing, and is load independent since it does not require an access to the medium. Moreover, we show that our RARE approach performs well in a real radio environment through a number of experiments performed on a static 17 node WLAN mesh testbed.
    Communications, 2007. ICC '07. IEEE International Conference on; 07/2007
  • Karol Kowalik, Martin Collier
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    ABSTRACT: Quality of Service (QoS) routing methods are expected to replace existing intradomain routing protocols in future QoS-based data networks. QoS routing allows the selection of feasible paths for connections requiring QoS support. Link state QoS routing performs path selection based on traffic parameters carried within the requests and information about available network resources provided by link state advertisements. A good link state QoS routing method should efficiently utilise networking resources and should incur little overhead in spreading information about resource availability.When a network implements load sensitive routing, traffic fluctuations are often observed which give rise to routing instability. This results in poor route selection and an overall degradation of network performance. Such oscillatory behaviour may be expected in datagram networks, because of their rapid response to routing updates, but it is not peculiar to them. It also affects virtual circuit networks, when the update interval is comparable with the average duration of a connection.In this paper we present methods for reducing this effect in virtual circuit networks. The first method—ALCFRA (Adaptive Link Cost Function Routing Algorithm) can be used in networks with sparse connectivity, while the second algorithm—CAR (Connectivity Aware Routing) is designed to work well in the majority of network topologies. Such methods improve the routing stability, which in turn leads to a higher acceptance ratio of arriving connections. The route selection improvements presented in this paper not only stabilise the link state QoS routing methods, but also achieve excellent performance over a variety of network topologies.
    Computer Networks 10/2006; DOI:10.1016/j.comnet.2005.03.005 · 1.28 Impact Factor
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    K. Kowalik, M. Collier
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    ABSTRACT: It is said that a picture is worth a thousand words - this statement also applies to networking topics. Thus, to effectively monitor network performance we need tools which present the performance metrics in a graphical way which is also clear and informative. We propose a tool for this purpose which we call the traffic engineering eye diagram (TEED). Eye diagrams are used in digital communications to analyse the quality of a digital signal; the TEED can similarly he used in the traffic engineering field to analyse the load balancing ability of a TE algorithm. In this paper we describe how to create such TEEDs and how to use them to analyse and compare various traffic engineering approaches.
    Consumer Communications and Networking Conference, 2005. CCNC. 2005 Second IEEE; 02/2005
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    ABSTRACT: The deployment of MPLS has been motivated by its potential for traffic engineering, and for supporting flows requiring QoS guarantees. However, the connectionless service available in MPLS incurs a considerable overhead due to the label management required. We advocate the use of a new protocol to support connectionless traffic in an MLPS-friendly way, called subIP. subIP uses the MPLS packet format with minimal changes, and thus interoperates easily with MPLS, but supports best-effort traffic with no signalling or label management overhead. It supports multipath routing through the use of multiple virtual network topologies. We present a Virtual Topology Algorithm to map incoming traffic onto multiple topologies for load balancing purposes. Simulations show that this algorithm can give rise to a significant improvement in network utilization.
    Networking - ICN 2005, 4th International Conference on Networking, ReunionIsland, France, April 17-21, 2005, Proceedings, Part II; 01/2005
  • Source
    Karol Kowalik, Martin Collier
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    ABSTRACT: Abstract Quality of Service (QoS) routing methods,are expected to replace existing routing protocols in future QoS-based data networks. QoS routing allows the selection of feasible paths for connections requiring QoS support. A good QoS routing method,should efficiently utilise networking,resources and the overhead involved in spreading information about resource availability should be low. Topology aggregation has been proposed,as a method,to reduce this overhead and allow scalability to large networks. It is used in the PNNI routing protocol which has been standardised for ATM networks. There are several aggregation methods proposed by researchers. PNNI does not restrict aggregation to only one technique, stating only that: “the symmetric star topology is used as the ‘default node representation’” [1]. This paper explores the performance,of PNNI routing when,various aggregation methods coexist in a single network with two hierarchical levels, within a game-theoretic framework. It is shown,that in such a scenario typical aggregation methods,can give a rise to a “tragedy of the commons”. Improved performance,is shown,to result after adopting a new,rule governing the manner in which state information is shared.
    MMB & PGTS 2004, 12th GI/ITG Conference on Measuring and Evaluation of Computer and Communication Systems (MMB) together with 3rd Polish-German Teletraffic Symposium (PGTS), September 12-15, 2004, Dresden, Germany; 01/2004
  • Source
    K. Kowalik, M. Collier
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    ABSTRACT: Multimedia traffic and real-time e-commerce applications can experience quality degradation in traditional networks such as the Internet. These difficulties can be overcome in networks which feature dynamically set up paths with bandwidth and delay guarantees. The problem of selecting such constrained paths is the task of quality of service (QoS) routing. This paper considers link-state routing, and the choice of cost metric used to implement QoS routing. There are two schools of thought regarding the choice of link cost. It is commonly assumed that QoS routing algorithms should limit hop count so as to conserve resources for future connections. Others advocate load balancing mechanisms so as to increase overall network utilisation. This paper investigates which of these approaches gives the better performance. We show that there is no one general answer to this question. We also point out the dangers of drawing general conclusions about routing algorithm performance based on the study of only a limited set of network topologies.
    Communications, 2003. ICC '03. IEEE International Conference on; 06/2003
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    ABSTRACT: High-end networking applications such as e-commerce, multimedia, distributed data analysis and advanced collaborative environments feature demanding end-to-end quality of service (QoS) requirements. Due to the heterogeneity exhibited by the Internet, a route from source to destination for such a flow may not be available which is comprised exclusively of QoS supporting path segments. Hence the flow must traverse one or more non-QoS path segments referred to here as reservation gaps. In this paper we study the problem of reservation gaps and their impact on QoS and present a solution to address the deficiencies caused by such gaps, using an active network approach based on the mobile agent paradigm. Furthermore, to improve the reliability in path selection and to minimise the influence of reservation gaps along the path of a QoS flow, we propose two routing algorithms, the most reliable shortest path (MS-R) algorithm and the shortest - most reliable path (S-MR) algorithm, that select paths with the minimum number of reservation gaps. The active network based solution we propose works autonomously and scales to large networks such as the Internet. We demonstrate the advantages of such a solution using simulations which compares operational characteristics of QoS flows when traversing non-managed and actively managed reservation gaps. We also demonstrate the benefits of employing a routing algorithm such as MR-S or S-MR that accounts for reservation gaps in place of conventional shortest-path routing algorithms.
    Communications, 2003. ICC '03. IEEE International Conference on; 06/2003
  • Source
    K. Kowalik, M. Collier
    [Show abstract] [Hide abstract]
    ABSTRACT: Multimedia traffic and real-time e-commerce applications can experience quality degradation in traditional networks such as the Internet. These difficulties can be overcome in networks which feature dynamically set up paths with bandwidth and delay guarantees. The problem of selecting such constrained paths is the task of quality of service (QoS) routing. Researchers have proposed several ways of implementing QoS routing, preferring either mechanisms which distribute network load or algorithms which conserve resources. Our previous studies have shown that network connectivity is an important factor when deciding which of these two approaches gives the best performance. In this paper we propose an algorithm, which features both load distribution and resource conservation. It takes a hybrid approach which balances between these two extreme approaches, according to the level of network connectivity. Our simulations indicate that this algorithm offers excellent performance over a than existing algorithms.
    Computers and Communication, 2003. (ISCC 2003). Proceedings. Eighth IEEE International Symposium on; 01/2003
  • Source
    Karol Kowalik, Martin Collier
    [Show abstract] [Hide abstract]
    ABSTRACT: Multimedia traffic and real-time e-commerce applications can experience quality degradation in traditional networks such as the Internet. These problems can be overcome in networks which feature dynamically set up paths with bandwidth and delay guarantees. Multi Protocol Label Switching (MPLS) shows promise as a networking protocol which can provide such capabilities. However, existing routing protocols need to be enhanced or replaced by QoS-aware algorithms if this potential is to be realised.
  • Source
    Karol Kowalik, Martin Collier
    [Show abstract] [Hide abstract]
    ABSTRACT: Multimedia traffic and real-time e-commerce applications can experience quality degradation in traditional networks such as the Internet. These problems can be overcome in networks which feature dynamically set up paths with bandwidth and delay guarantees. Multi Protocol Label Switching (MPLS) shows promise as a networking protocol which can provide such capabilities. However, existing routing protocols need to be enhanced or replaced by QoS-aware algorithms if this potential is to be realised. This paper presents a survey of emerging QoS routing methods for unicast flows suitable for usage within MPLS networks. We discuss basic algorithms such as Widest Shortest Path (WSP) and more complicated ones such as the Minimum Interference Routing (MIRA) or ProfileBased Routing. Then we propose a new QoS routing algorithm for Diff-Serv flows in MPLS networks. The method has two phases: off-line routing - based on daily statistics, which achieves efficient global network utilisation
  • Source
    Karol Kowalik, Mark Davis
    [Show abstract] [Hide abstract]
    ABSTRACT: Wireless Mesh Networks (WMNs) are a type of radio-based net-work systems which require minimal configuration and infrastructure. They can be build using relatively low cost radios and inexpensive computing platforms, and consequently appear to be a compelling option for rolling out networks with a low deployment cost. One of the factors which influences the performance of WMNs is the routing protocol used. There are many routing protocols for WMNs, we estimate that there are more than a hundred of them. In this paper we attempt to answer the question why there are so many and if there is a need for such an abundance. Moreover, we elaborate on the possible development of a single routing protocol for WMNs.
  • Source
    Karol Kowalik, Martin Collier
    [Show abstract] [Hide abstract]
    ABSTRACT: Quality of Service (QoS) routing methods are expected to replace existing routing protocols in future QoS-based data networks. QoS routing allows the selection of feasible paths for connections requiring QoS support. A good QoS routing method should efficiently utilise networking resources and the over- head involved in spreading information about resource availability should be low. Topology aggregation has been proposed as a method to reduce this overhead and allow scalability to large networks. It is used in the PNNI routing protocol which has been standardised for ATM networks. There are several aggregation methods proposed by researchers. PNNI does not restrict aggregation to only one technique, stating only that: "the symmetric star topology is used as the 'default node representation'" (1). This paper explores the performance of PNNI routing when various aggregation methods coexist in a single network with two hierarchical levels, within a game-theoretic framework. It is shown that in such a scenario typical aggregation methods can give a rise to a "tragedy of the commons". Improved performance is shown to result after adopting a new rule governing the manner in which state information is shared.

Publication Stats

119 Citations
1.28 Total Impact Points

Institutions

  • 2007–2009
    • Dublin Institute of Technology
      Dublin, Leinster, Ireland
  • 2003–2006
    • Dublin City University
      • Research Institute for Networks and Communications Engineering (Rince)
      Dublin, Leinster, Ireland