Arek Dadej

Matching graphs with unique node labels

A special class of graphs is introduced in this paper. The graphs belonging to this class are characterised by the existence of unique node labels. A number of matching algorithms for graphs with unique node labels are developed. It is shown that problems such as graph isomorphism, subgraph isomorphism, maximum common subgraph (MCS) and graph edit distance (GED) have a computational complexity that is only quadratic in the number of nodes. Moreover, computing the median of a set of graphs is only linear in the cardinality of the set. In a series of experiments, it is demonstrated that the proposed algorithms run very fast in practice. The considered class makes the matching of large graphs, consisting of thousands of nodes, computationally tractable. We also discuss an application of the considered class of graphs and related matching algorithms to the classification and detection of abnormal events in computer networks.

On graphs with unique node labels

A special class of graphs is introduced in this paper. The graphs belonging to this class are characterised by the existence of unique node labels. A number of matching algorithms for graphs with unique node labels are developed. It is shown that problems such as graph isomorphism, subgraph isomorphism, maximum common subgraph and others have a computational complexity that is only quadratic in the number of nodes. We also discuss some potential applications of the considered class of graphs.

Proactive context transfer and forced handover in IEEE 802.11 wireless LAN based access networks

In recent years, many protocols have been developed to support user mobility in wireless networks, e.g. Mobile IP suite of protocols designed to support IP routing to mobile nodes. However, support for truly seamless mobility requires more than just routing: every service associated with the mobile user needs to be transferred smoothly to the new access network. In this paper, we will concentrate on the problem of transferring service state (context) at both the link and the IP layers. We propose a method to estimate the best moment in time for transferring context information associated with the mobile user. As one of key issues in the proactive context transfer scheme is accuracy of handover prediction, we suggest and describe a new concept of Forced Handover that can provide very low handover latency. The simulation results and the following discussions show that our scheme is helpful in ensuring seamless mobility, while keeping the number of unnecessary handovers resulting from the proactive nature of the scheme at a controllable level.

Proactive context transfer in WLAN-based access networks

In recent years, many protocols have been developed to support mobility of wireless network nodes, e.g. Mobile IP suite of protocols designed to support IP routing to mobile nodes. However, support for truly seamless mobility requires more than just routing; every service associated with the mobile user needs to be transferred smoothly to the new access network. In this paper, we consider the problem of transferring service state (context) at both the link and IP layers. Based on the rate of SNR change in the wireless access channel, we propose a scheme that proactively transfers context information associated with the mobile user. The proposed scheme estimates the best moment in time for transferring context information, to assure the shortest waiting time of the transferred context at the new access network. We also propose and describe a new concept, forced handover, helpful in proactive transfer of context information when the mobile node moves from one access sub network to another. We present preliminary simulation results and a discussion on the performance of the proposed scheme. The scheme is shown to be helpful in ensuring seamless mobility, while the number of unnecessary handovers resulting from the proactive nature of the scheme can be kept at a controllable level.

OPNET simulation modeling and analysis of enhanced Mobile IP

To facilitate simulation studies of Mobile IP performance and comparative analysis of enhanced mobile IP handover mechanisms, we have developed a simulation model of Mobile IP using OPNET modeling environment. In this paper, we provide basic design concepts and implementation details of the simulation model, as well as descriptions of the advanced features of IP mobility architectures implemented as part of the model, e.g. buffering and regional registration. Based on the analysis of simulation results obtained using the developed simulation models, a few suggestions are made for the use of Mobile IP and related enhanced mechanisms in selected wireless Internet scenarios.

SIMILARITY MEASURES FOR HIERARCHICAL REPRESENTATIONS OF GRAPHS WITH UNIQUE NODE LABELS

A hierarchical abstraction scheme based on node contraction and two related similarity measures for graphs with unique node labels are proposed in this paper. The contraction scheme reduces the number of nodes in a graph and leads to a speed-up in the computation of graph similarity. Theoretical properties of the new graph similarity measures are derived and experimentally verified. A potential application of the proposed graph abstraction scheme in the domain of computer network monitoring is discussed.

Hybrid Quality of Service Architecture for Wireless/Mobile Environment

Provision of Quality of Service (QoS) guarantees for multimedia applications over IP networks is rapidly becoming a critical research and design issue, especially within the radio access segment of the next generation wireless/mobile environment. While the simple and scalable Differentiated Services (DiffServ) QoS control model is suitable for the core part of the network, more explicit, admission and reservation based QoS mechanisms are required in the wireless access segment of the network where the resources available and the levels of traffic aggregation render the DiffSery principles less effective. We present a suitable hybrid QoS architecture framework, and then study the relevant issues further for a radio access network based on IEEE 802.11 WLAN with 802.11e QoS extensions.

Link Change and Generalized Mobility Metric for Mobile Ad-hoc Networks

Since the performance of a mobile ad-hoc network (MANET) is strongly affected by the frequency of link change due to node mobility, there is a need to study thoroughly the characteristics of link dynamics. Link properties, such as link duration, link change rate and link availability, have been studied in several researches. However, they do not reflect thoroughly the network dynamics. In this paper, we propose a link property that reflects the network dynamics in generalized manner as it is independent of the mobility model assumed and the number of nodes in the network. We develop an analytical framework for calculating the probability of link change, including link creation and link breakage. And as a result, the probability density function of the distance between two nodes is also derived. There are many applications of the probability of link change in MANETs, such as network design, routing protocol optimization and network performance evaluation. As an illustration, we have proposed an application of the probability of link change in the previous paper as a generalized mobility metric for characterizing topology dynamics in MANETs

A framework for performance evaluation of self-organising networks

This paper proposes a qualitative framework of performance measures for evaluating the performance of self-organising radio networks, aimed at capturing the important behavioural aspects of the self-organisation process, in a way that should prove useful to both network users and network operators. Where the proposed measures have previously been shown to be useful, appropriate references are cited and discussed.

Adding Support for Satellite Interfaces to 802.21 Media Independent Handover

Mobile devices are now equipped with a broad range of wireless interfaces to connect to various access networks. Different terrestrial and satellite access networks are needed to ensure ubiquitous internet connectivity across all possible locations of mobile terminals. To support uninterrupted communications for mobile terminals in a heterogeneous wireless access environment, the IEEE 802.21 Media Independent Handover framework has been defined. This framework, however, does not include support for satellite networks, one of the key technologies in providing wireless data connectivity where wireless access infrastructure is not available (e.g. sparsely populated remote areas, see and air travel). In this work, we define and propose a reference model that allows link layer information from satellite interfaces to be presented to upper layers much like link layer information from other terrestrial interfaces supported by IEEE 802.21. Our proposal facilitates efficient Media Independent Handovers in heterogeneous access environments involving satellite networks. The satellite interface model used in this work is based on the IP-based satellite network architecture defined by ETSI, however it can be extended to cover other satellite link interface models as required.