In recent years huge potential benefits from novel applications in mobile ad hoc networks (MANET) have been discussed extensively. However, without robust security mechanisms and systems to provide safety shell through the MANET infrastructure, MANET applications can be vulnerable and hammered by malicious attackers easily. In order to detect misbehaved message routing and identify malicious attackers in MANET, schemes based on reputation concept have shown their advantages in this area in terms of good scalability and simple threshold-based detection strategy. We observed that previous reputation schemes generally use predefined thresholds which do not take into account the effect of behavior dynamics between nodes in a period of time. In this paper, we propose a Threshold-Adaptive Reputation System (TARS) to overcome the shortcomings of static threshold strategy and improve the overall MANET performance under misbehaved routing attack. A fuzzy-based inference engine is introduced to evaluate the trustiness of a node's one-hop neighbors. Malicious nodes whose trust values are lower than the adaptive threshold, will be detected and filtered out by their honest neighbors during trustiness evaluation process. The results of network simulation show that the TARS outperforms other compared schemes under security attacks in most cases and at the same time reduces the decrease of total packet delivery ratio by 67% in comparison with MANET without reputation system.

The performance of symmetric and asymmetric cryptography algorithms in small devices is presented. Both temporal and energy costs are measured and compared with the basic functional costs of a device. We demonstrate that cryptographic power costs are not a limiting factor of the autonomy of a device and explain how processing delays can be conveniently managed to minimize their impact.

In the meantime, most secure ad hoc routing protocols based on cryptography just have assumed that pair-wise secret keys or public keys were distributed among nodes before running a routing protocol. In this paper, we raise a question about key management related to existing secure routing protocols, and then we propose an authenticated on-demand ad hoc routing protocol with key exchange by applying the ID-based keyed authenticator. In particular, we focus on providing an authentication mechanism to Dynamic Source Routing protocol combined with Diffie-Hellman key exchange protocol, and then we demonstrate simulated performance evaluations. The main contribution of our work is to provide a concurrent establishment of a route and a session key in a secure manner between source and destination nodes in ad hoc networks.

Routing algorithms with low overhead, stable link and independence of the total number of nodes in the network are essential for the design and operation of the large-scale wireless mobile ad hoc networks (MANET). In this paper, we develop and analyze the Cluster Based Location-Aided Routing Protocol for MANET (C-LAR), a scalable and effective routing algorithm for MANET. C-LAR runs on top of an adaptive cluster cover of the MANET, which can be created and maintained using, for instance, the weight-based distributed algorithm. This algorithm takes into consideration the node degree, mobility, relative distance, battery power and link stability of mobile nodes. The hierarchical structure stabilizes the end-to-end communication paths and improves the networks' scalability such that the routing overhead does not become tremendous in large scale MANET. The clusterheads form a connected virtual backbone in the network, determine the network's topology and stability, and provide an efficient approach to minimizing the flooding traffic during route discovery and speeding up this process as well. Furthermore, it is fascinating and important to investigate how to control the total number of nodes participating in a routing establishment process so as to improve the network layer performance of MANET. C-LAR is to use geographical location information provided by Global Position System to assist routing. The location information of destination node is used to predict a smaller rectangle, isosceles triangle, or circle request zone, which is selected according to the relative location of the source and the destination, that covers the estimated region in which the destination may be located. Thus, instead of searching the route in the entire network blindly, C-LAR confines the route searching space into a much smaller estimated range. Simulation results have shown that C-LAR outperforms other protocols significantly in route set up time, routing overhead, mean delay and packet collision, and simultaneously maintains low average end-to-end delay, high success delivery ratio, low control overhead, as well as low route discovery frequency.

Wireless ad hoc networks have fundamentally altered today's battlefield, with applications ranging from unmanned air vehicles to randomly deployed sensor networks. Security and vulnerabilities in wireless ad hoc networks have been considered at different layers, and many attack strategies have been proposed, including denial of service (DoS) through the intelligent jamming of the most critical packet types of flows in a network. This paper investigates the effectiveness of intelligent jamming in wireless ad hoc networks using the Dynamic Source Routing (DSR) and TCP protocols and introduces an intelligent classifier to facilitate the jamming of such networks. Assuming encrypted packet headers and contents, our classifier is based solely on the observable characteristics of size, inter-arrival timing, and direction and classifies packets with up to 99.4% accuracy in our experiments.

Flooding is an indispensable operation for providing control or routing functionalities to mobile ad hoc networks (MANETs). Previously, many flooding schemes have been studied with the intention of curtailing the problems of severe redundancies, contention, and collisions in traditional implementations. A recent approach with relatively high efficiency is 1HI by Liu et al., which uses only 1-hop neighbor information. The scheme achieves local optimality in terms of the number of retransmission nodes with time complexity Θ(nlog n), where n is the number of neighbors of a node; however, this method tends to make many redundant transmissions. In this paper, we present a novel flooding algorithm, 2HBI (2-hop backward information), that efficiently reduces the number of retransmission nodes and solves the broadcast storm problem in ad hoc networks using our proposed concept, "2-hop backward information." The most significant feature of the proposed algorithm is that it does not require any extra communication overhead other than the exchange of 1-hop HELLO messages but maintains high deliverability. Comprehensive computer simulations show that the proposed scheme significantly reduces redundant transmissions in 1HI and in pure flooding, up to 38% and 91%, respectively; accordingly it alleviates contention and collisions in networks.

Transient routing loops have been observed to form in Mobile Ad-hoc Networks running the OLSRv2 proactive link-state routing protocol. The packets falling into loops impact the surrounding network thus degrading throughput even though only a small proportion of the traffic may enter these loops and only for a short time. This becomes significantly more evident when Link Layer Notification is used to catch broken links, inadvertently leading to an increase in the number of loops. Two methods of Loop Detection are introduced and are used to trigger either Loop Suppression by selectively and preemptively discarding the looping packets that are unlikely to reach their destination, or Loop Correction by the notification of the routing protocol to cut the link over which the packet is looping. The newly introduced Loop Suppression and Loop Correction techniques used with Link Layer Notification are shown to significantly increase network performance over plain OLSRv2 and OLSRv2 with Link Layer Notification.

A Policy-based Network Management (PBNM) in Mobile Ad-hoc Networks (MANETs) should be efficient and reliable. In this letter, we propose a mechanism for the policy-based management in ad hoc networks and we discuss methods to discover the Policy Decision Point (PDP), set the management area, and manage the movements of nodes in the PBNM system. Finally, we assess the results through simulations.

A typical feature of MANETs is that network topology is dynamically changed by node movement. When we execute state transition testing for such protocols, first we draw the Finite State Machine (FSM) with respect to each number of neighbor nodes. Next, we create the state transition matrix from the FSMs. Then, we generate test cases from the state transition matrix. However, the state transition matrix is getting much large because the number of states and the number of transitions increase explosively with increase of the number of neighbor nodes. As a result, the number of test cases increases, too. In this paper, we propose a new method to reduce the number of test cases by using equivalent division method. In this method, we decide a representative input to each state, which is selected from equivalent inputs to the states. By using our proposed method, we can generate state transition matrix which is hard to affect increasing the number of neighbor nodes. As a consequence, the number of test cases can be reduced.

Slotted wireless ad hoc networks are drawing more and more attention because of their advantage of QoS (Quality of Service) support for multimedia applications owing to their collision-free packet transmission. Time slot assignment is an unavoidable and important problem in such networks. The existing time slot assignment methods have in general a drawback of limited available bandwidth due to their local assignment optimization without the consideration of directions of the radio wave transmission of wireless links along the routes in such networks. A new time slot assignment is proposed in this paper in order to overcome this drawback. The proposed assignment is different from the existing methods in the following aspects: a) consideration of link directions during time slot assignment; b) largest bandwidth to be achieved; c) feasibility in resource limited ad hoc networks because of its fast assignment. Moreover, the effectiveness of the proposal is confirmed by some simulation results.

The research on Delay Tolerant Networks (DTN) has been activated aiming at a variety of potential applications toward ubiquitous society. The vehicular network is one of the promising areas for applying DTN. In this paper, the end-to-end delay characteristics for vehicular ad-hoc broadcast DTN is analyzed, where the dynamic vehicle mobility model is introduced. The analysis is applied to the two realistic road models, that is, one-way and two-way traffic models. The simulation study demonstrates validity of our analysis for use in generic vehicle networks.

The usable throughput of an IEEE 802.11 system for an application is much less than the raw bandwidth. Although 802.11b has a theoretical maximum of 11 Mbps, more than half of the bandwidth is consumed by overhead leaving at most 5 Mbps of usable bandwidth. Considering this characteristic, this paper proposes and analyzes a real-time distributed scheduling scheme based on the existing IEEE 802.11 wireless ad-hoc networks, using USC/ISI's Power Aware Sensing Tracking and Analysis (PASTA) hardware platform. We compared the distributed real-time scheduling scheme with the real-time polling scheme to meet deadline, and compared a measured real bandwidth with a theoretical result. The theoretical and experimental results show that the distributed scheduling scheme can guarantee real-time traffic and enhances the performance up to 74% compared with polling scheme.

A mobile node in ad hoc networks may move arbitrarily and act as a router and a host simultaneously. Such a characteristic makes nodes in MANET vulnerable to potential attacks. The black hole problem, in which some malicious nodes pretend to be intermediate nodes of a route to some given destinations and drop packets that pass through it, is one of the major types of attack. In this paper, we propose a distributed and cooperative mechanism to tackle the black hole problem. The mechanism is distributed so that it suits the ad hoc nature of network, and nodes in the protocol cooperate so that they can analyze, detect, and eliminate possible multiple black-hole nodes in a more reliable fashion. Simulation results show that our method achieves a high black hole detection rate and good packet delivery rate, while the overhead is comparatively lower as the network traffic increases.

Multicast communication over mobile ad hoc networks has become popular. However, dependable and scalable multicast routing is required for mobile ad hoc networks even though network size and node mobility continue to increase. Therefore, this paper proposes a new hierarchical multicast routing scheme for such ad hoc networks. The proposed scheme introduces the inter-cluster group mesh structure based on our previous autonomous clustering proposal. In the proposed scheme, data packets are delivered from the source node to the multicast members through multiple routes over the inter-cluster group mesh structure. Simulations show that the proposed scheme is scalable with regard to network size and strong against node mobility; it can provide dependable multicast communication on large mobile ad hoc networks.

A novel timing synchronizing scheme is proposed for use in inter-vehicle communication (IVC) with an autonomous distributed intelligent transport system (ITS). The scheme determines the timing of packet signal transmission in the IVC network and employs the guard interval (GI) timing in the orthogonal frequency divisional multiplexing (OFDM) signal currently used for terrestrial broadcasts in the Japanese digital television system (ISDB-T). This signal is used because it is expected that the automotive market will demand the capability for cars to receive terrestrial digital TV broadcasts in the near future. The use of broadcasts by automobiles presupposes that the on-board receivers are capable of accurately detecting the GI timing data in an extremely low carrier-to-noise ratio (CNR) condition regardless of a severe multipath environment which will introduce broad scatter in signal arrival times. Therefore, we analyzed actual broadcast signals received in a moving vehicle in a field experiment and showed that the GI timing signal is detected with the desired accuracy even in the case of extremely low-CNR environments. Some considerations were also given about how to use these findings.

IEEE 802.11 MAC is the most commonly used protocol in multi-hop ad-hoc networks which need no infrastructure. In multi-hop ad-hoc networks based on IEEE 802.11, since nodes try transmitting their packets at every possible slot, there is a high packet loss probability. This degrades network performance attributes such as throughput and fairness. In this paper, we focus on achieving the maximum throughput of the given network topology by adding extra backoff time to random backoff time based on IEEE 802.11. Specifically, the optimal load rate is obtained with constraints of Carrier Sensing Multiple Access/Collision Avoidance (CSMA/CA) mechanism.

IEEE 802.11 Media Access Control (MAC) is the most widely used protocol in Wireless Ad-hoc Networks (WANETs). However, it cannot guarantee fair channel allocation among the flows contending for the channel. In this paper, we propose a new media access control algorithm to achieve per-flow fairness while maximizing WANETs throughput.

Mobile Ad Hoc Networks (MANETs) are temporal and infrastructure-independent wireless networks that consist of mobile nodes. For instance, a MANET can be used as an emergent network for communication among people when a disaster occurred. Since there is no central server in the network, each node has to find out its desired information (objects) by itself. Constructing a mobile Peer-to-Peer (P2P) network over the MANET can support the object search. Some researchers proposed construction schemes of mobile P2P networks, such as Ekta and MADPastry. They integrated DHT-based application-layer routing and network-layer routing to increase search efficiency. Furthermore, MADPastry proposed a clustering method which groups the overlay nodes according to their physical distance. However, it has also been pointed out that the search efficiency deteriorates in highly dynamic environments where nodes quickly move around. In this paper, we focus on route disappearances in the network layer which cause the deterioration of search efficiency. We describe the detail of this problem and evaluate quantitatively it through simulation experiments. We extend MADPastry by introducing a method sharing objects among nodes in a cluster. Through simulation experiments, we show that the proposed method can achieve up to 2.5 times larger success rate of object search than MADPastry.

This paper presents a fully self-organized key management scheme for mobile ad hoc networks. Unlike most previous schemes, there is no priori shared secret or no priori trust relationship in the proposed scheme; every node plays the same role and carries out the same function of key management. The proposed scheme consists of (1) Handshaking (HS) and (2) Certificate request/reply (CRR) procedures. In HS, a node acquires the public key of the approaching node via a secure side channel. In CRR, a node requests certificates of a remote node via a radio channel to the nodes that it has HSed. If the number of received valid certificates that contain the same public key exceeds a given threshold, the node accepts the remote node's public key as valid. Security is rigorously analyzed against various known attacks and network costs are intensively analyzed mathematically. Using this analysis, we provide parameter selection guideline to optimize performance and to maintain security for diverse cases. Simulation results show that every node acquires the public keys of all other nodes at least 5 times faster than in a previous scheme.

In wireless ad hoc networks, providing an authentication service to verify that the broadcast packet is from the claimed sender without modification, is challenging due mainly to the inherently lossy wireless links. This paper presents a novel Secure and Reliable Broadcasting that reinforces the broadcast authentication with reliability and energy-efficiency capabilities by using the cooperative diversity to superimpose two distinct signals. The proposed protocol achieves significant savings of transmission power and fair assurance of reliability among receivers.