King-Shan Lui

DelPHI: wormhole detection mechanism for ad hoc wireless networks

In mobile ad hoc networks, data transmission is performed within an untrusted wireless environment. Various kinds of attack have been identified and corresponding solutions have been proposed. Wormhole attack is one of the serious attacks which forms a serious threat in the networks, especially against many ad hoc wireless routing protocols and location-based wireless security system. We identify two types of wormhole attacks. In the first type, malicious nodes do not take part in finding routes, meaning that, legitimate nodes do not know their existence. In the second type, malicious nodes do create route advertisements and legitimate nodes are aware of the existence of malicious nodes, just do not know they are malicious. Some researchers have proposed detection mechanisms for the first type. In this paper, we propose an efficient detection method called delay per hop indication (DelPHI). By observing the delays of different paths to the receiver, the sender is able to detect both kinds of wormhole attacks. This method requires neither synchronized clocks nor special hardware equipped mobile nodes. The performance of DelPHI is justified by simulations.

Routing with topology aggregation in delay-bandwidth sensitive networks

Routing is a process of finding a network path from a source node to a destination node. The execution time and the memory requirement of a routing algorithm increase with the size of the network. In order to deal with the scalability problem, large networks are often structured hierarchically by grouping nodes into different domains. The internal topology of each domain is then aggregated into a simple topology that reflects the cost of routing across that domain. This process is called topology aggregation. For delay-bandwidth sensitive networks, traditional approaches represent the property of each link in the aggregated topology as a delay-bandwidth pair, which corresponds to a point on the delay-bandwidth plane. Since each link after aggregation may be the abstraction of many physical paths, a single delay-bandwidth pair results in significant information loss. The major contribution of this paper is a novel quality-of-service (QoS) parameter representation with a new aggregation algorithm and a QoS-aware routing protocol. Our QoS representation captures the state information about the network with much greater accuracy than the existing algorithms. Our simulation results show that the new approach achieves very good performance in terms of delay deviation, success ratio, and crankback ratio.

A distributed multihop time synchronization protocol for wireless sensor networks using Pairwise Broadcast Synchronization

Recently, a time synchronization algorithm called pairwise broadcast synchronization (PBS) is proposed. With PBS, a sensor can be synchronized by overhearing synchronization packet exchange among its neighbouring sensors without sending out any packet itself. In an one-hop sensor network where every node is a neighbour of each other, a single PBS message exchange between two nodes would facilitate all nodes to synchronize. However, in a multi-hop sensor network, PBS message exchanges in several node pairs are needed in order to achieve network-wide synchronization. To reduce the number of message exchanges, these node pairs should be carefully chosen. In this paper, we investigate how to choose these ldquoappropriaterdquo sensors aiming at reducing the number of PBS message exchanges while allowing every node to synchronize. This selection problem is shown to be NP-complete, for which the greedy heuristic is a good polynomial-time approximation algorithm. Nevertheless, a centralized algorithm is not suitable for wireless sensor networks. Therefore, we develop a distributed heuristic algorithm allowing a sensor to determine how to synchronize itself based on its neighbourhood information only. The protocol is tested through extensive simulations. The simulation results reveal that the proposed protocol gives consistent performance under different conditions with its performance comparable to that of the centralized algorithm.

QoS extension to BGP

To enable the end-to-end quality of service (QoS) guarantees in the Internet, based on the border gateway protocol (BGP), inter-domain QoS advertising and routing are important. However, little research has been done in this area so far. Two major challenges, scalability and heterogeneity, make the QoS extension to BGP difficult. Two existing approaches, link capacity routing (LCR) and available bandwidth routing (ABR), address QoS advertising and routing in BGP with respect to the bandwidth metric, but neither of them can solve the two challenges well. We extend BGP to advertise bandwidth information, but, instead of using link capacities or instantaneous available bandwidth values, a novel QoS metric, available bandwidth index (ABI), is defined and used to perform bandwidth advertising and routing. The two major contributions of ABI are: (1) ABI dynamically abstracts available bandwidth into a probability interval, therefore, it is very flexible to represent heterogenous and dynamic bandwidth values; (2) by capturing the statistical property of the detailed available bandwidth distribution, ABI is so efficient that it can highly decrease the message overhead in routing, thereby making the QoS advertising and routing very scalable. Our extensive simulations confirm both contributions of the ABI extension to BGP very well.

STAR: a transparent spanning tree bridge protocol with alternate routing

With increasing demand for multimedia applications, local area network (LAN) technologies are rapidly being upgraded to provide support for quality of service (QoS). In a network that consists of an interconnection of multiple LANs via bridges, the QoS of a flow depends on the length of an end-to-end forwarding path. In the IEEE 802.1D standard for bridges, a spanning tree is built among the bridges for loop-free frame forwarding. Albeit simple, this approach does not support all-pair shortest paths. In this paper, we present a novel bridge protocol, the Spanning Tree Alternate Routing (STAR) Bridge Protocol, that attempts to find and forward frames over alternate paths that are provably shorter than their corresponding tree paths. Being backward compatible to IEEE 802.1D, our bridge protocol allows cost-effective performance enhancement of an existing extended LAN by incrementally replacing a few bridges in the extended LAN by the new STAR bridges. We develop a strategy to ascertain bridge locations for maximum performance gain. Our study shows that we can significantly improve the end-to-end performance when deploying our bridge protocol.

Analysis of Topology Aggregation techniques for QoS routing

We study and compare topology aggregation techniques used in QoS routing. Topology Aggregation (TA) is defined as a set of techniques that abstract or summarize the state information about the network topology to be exchanged, processed, and maintained by network nodes for routing purposes. Due to scalability, aggregation techniques have been an integral part of some routing protocols. However, TA has not been studied extensively except in a rather limited context. With the continuing growth of the Internet, scalability issues of QoS routing have been gaining importance. Therefore, we survey the current TA techniques, provide methodology to classify, evaluate, and compare their complexities and efficiencies.

J-CAR: An efficient joint channel assignment and routing protocol for IEEE 802.11-based multi-channel multi-interface mobile Ad Hoc networks

The capacity of an IEEE 802.11-based multi-hop wireless network is limited. By effectively utilizing multiple non-overlapping channels and multiple interfaces, collision and co-channel interference can be reduced. This allows more concurrent transmissions and thus enhances the network capacity. In this paper, we introduce an efficient distributed joint channel assignment and routing protocol, called J-CAR. Unlike existing schemes, J-CAR allows a data interface to dynamically change its routing protocol working mode between send and receive on a call-by-call basis, which distributed joint channel assignment enhances the utilization of both interface and channel. In J-CAR, channels are negotiated and assigned to active links in conjunction with the on-demand routing process. At each hop, J-CAR conducts a local optimization by selecting the least interfered channel according to the channel interference index. The channel interference index is designed by taking both the protocol and physical interference models into consideration. To find the least interfered path for network load balancing on a global scale, J-CAR employs a length-constrained widest-path routing. The ldquowidthrdquo of a path is determined by the interference level of its bottleneck link. With an adjustable threshold on the path length (with respect to the shortest-path), the excessively long path can also be avoided. We show that with a comparable complexity as the existing schemes, J-CAR provides much higher system good puts and shorter end-to-end packet delays.

A Trust-Based Geographical Routing Scheme in Sensor Networks

Devices in a sensor network need to work in a hostile environment and they are usually powered by batteries. Yet the whole purpose of deploying a sensor network is to perform distributed collaborative computing, possibly in a massive scale. In a hostile computing environment, the sensor devices might be routinely tampered with. Together with the possibility of faulty devices due to extreme conditions or low power, the trustworthiness of a device varies. Specifically, a device should only communicate with another device which has a trust level above a certain threshold. However, setting up trusted communication channels among sensor devices remains a major challenge. In this paper, we propose a trust-based routing scheme in sensor networks for providing a high level of robustness in node selection based on packet trust requirement with lifetime consideration. Our protocol allows messages to be routed through malicious and faulty devices with the selection of trusted neighbors. On the other hand, the network lifetime can also be prolonged by selecting those with their sensing functions covered by some existing nodes. Simulation results show that our scheme is possible to prolong the lifetime of sensor networks and maintain certain satisfactory delivery ratio.

Using Micro-Genetic Algorithms to Improve Localization in Wireless Sensor Networks

Wireless sensor networks are widely adopted in many location-sensitive applications including disaster management, environmental monitoring, military applications where the precise estimation of each node position is inevitably important when the absolute positions of a relatively small portion as anchor nodes of the underlying network were predetermined. Intrinsically, localization is an unconstrained optimization problem based on various distance/path measures. Most of the existing localization methods focus on using different heuristic-based or mathematical techniques to increase the precision in position estimation. However, there were recent studies showing that nature-inspired algorithms like the ant-based or genetic algorithms can effectively solve many complex optimization problems. In this paper, we propose to adapt an evolutionary approach, namely a micro-genetic algorithm, as a post-optimizer into some existing localization methods such as the Ad-hoc Positioning System (APS) to further improve the accuracy of their position estimation. Obviously, our proposed MGA is highly adaptable and easily integrated into other localization methods. Furthermore, the remarkable improvements attained by our proposed MGA on both isotropic and anisotropic topologies of our simulation tests prompt for several interesting directions for further investigation.

Advertising interdomain QoS routing information

To enable end-to-end quality-of-service (QoS) guarantees in the Internet, based on the border gateway protocol (BGP), interdomain QoS information advertising, and routing are important. However, little research has been done in this area so far. Two major challenges, scalability and heterogeneity, make the QoS extension to BGP difficult. In the existing routing schemes, static and instantaneous QoS metrics, such as link capacity and available bandwidth, are used to represent QoS routing information, but neither of them can solve the two challenges well. In this paper, BGP is extended to advertise available bandwidth and delay information of routes, but, instead of using the traditional deterministic metrics, a series of statistical metrics, available bandwidth index (ABI), delay index (DI), available bandwidth histogram (ABH), and delay histogram (DH), are defined and applied to QoS information advertising and routing. Two major contributions of the proposed statistical metrics are: 1) QoS information is abstracted into one or several probability intervals and, thus, the heterogeneous and dynamic QoS information can be represented more flexibly and precisely and 2) by capturing the statistical property of the detailed distribution of QoS information, these new metrics are efficient and they can highly decrease the message overhead in routing, thereby making the QoS advertising and routing scalable. Our extensive simulations confirm both contributions of the QoS extension to BGP very well. Moreover, besides BGP, these statistical metrics can be applied to other networks and protocols to represent QoS information in a more scalable and precise way.