33,592 research outputs found

    Connectivity in ad-hoc and hybrid networks

    Get PDF
    We consider a large-scale wireless network, but with a low density of nodes per unit area. Interferences are then less critical, contrary to connectivity. This paper studies the latter property for both a purely ad-hoc network and a hybrid network, where fixed base stations can be reached in multiple hops. We assume here that power constraints are modeled by a maximal distance above which two nodes are not (directly) connected. We find that the introduction of a sparse network of base stations does significantly help in increasing the connectivity, but only when the node density is much larger in one dimension than in the other. We explain the results by percolation theory. We obtain analytical expressions of the probability of connectivity in the 1-dim. case. We also show that at a low spatial density of nodes, bottlenecks are unavoidable. Results obtained on actual population data confirm our findings

    Base Stations in Mobile Ad-Hoc Networks

    Get PDF
    Multi-hop ad-hoc networks consist of nodes which cooperate by forwarding packets for each other to allow communication beyond the power range of each node. In pure ad-hoc networks, no additional infrastructure is required to allow the nodes to communicate. Multi-hop hybrid networks are a combination of ad-hoc and cellular networks. As in ad-hoc networks, the nodes forward packets on behalf of other nodes. However, a few base stations are introduced. This enables long-range communication, increases connectivity and allows centralized services. In our work, we investigate the problem of placing base stations in multi-hop hybrid networks. Since nodes extend the service area by themselves, conventional cellular approaches are not suitable for such networks. We propose the Cluster Covering Algorithm, an algorithm which takes into account the percolation phenomenon, and compare it with several greedy algorithms. We measure the connectivity through different simulations on real population distribution data of Zurich (CH), the Surselva Valley (CH) and Finland. The simulation results show that the Cluster Covering Algorithm outperforms the greedy algorithms

    Secure Connectivity Through Key Predistribution Under Jamming Attacks In Ad Hoc and Sensor Networks

    Get PDF
    Wireless ad hoc and sensor networks have received attention from research communities over the last several years. The ability to operate without a fixed infrastructure is suitable for a wide range of applications which in many cases require protection from security attacks. One of the first steps to provide security is to distribute cryptographic keys among nodes for bootstrapping security. The unique characteristics of ad hoc networks create a challenge in distributing keys among limited resource devices. In this dissertation we study the impact on secure connectivity achieved through key pre-distribution, of jamming attacks which form one of the easiest but efficient means for disruption of network connectivity. In response to jamming, networks can undertake different coping strategies (e.g., using power adaptation, spatial retreats, and directional antennas). Such coping techniques have impact in terms of the changing the initial secure connectivity created by secure links through key predistribution. The objective is to explore how whether predistribution techniques are robust enough for ad hoc/sensor networks that employ various techniques to cope with jamming attacks by taking into account challenges that arise with key predistribution when strategies for coping with jamming attacks are employed. In the first part of this dissertation we propose a hybrid key predistribution scheme that supports ad hoc/sensor networks that use mobility to cope with jamming attacks. In the presence of jamming attacks, this hybrid scheme provides high key connectivity while reducing the number of isolated nodes (after coping with jamming using spatial retreats). The hybrid scheme is a combination of random key predistribution and deployment-based key predistribution schemes that have complementary useful features for secure connectivity. In the second part we study performance of these key predistribution schemes under other jamming coping techniques namely power adaptation and directional antennas. We show that the combination of the hybrid key predistribution and coping techniques can help networks in maintaining secure connectivity even under jamming attacks

    HYMAD: Hybrid DTN-MANET Routing for Dense and Highly Dynamic Wireless Networks

    Full text link
    In this paper we propose HYMAD, a Hybrid DTN-MANET routing protocol which uses DTN between disjoint groups of nodes while using MANET routing within these groups. HYMAD is fully decentralized and only makes use of topological information exchanges between the nodes. We evaluate the scheme in simulation by replaying real life traces which exhibit this highly dynamic connectivity. The results show that HYMAD outperforms the multi-copy Spray-and-Wait DTN routing protocol it extends, both in terms of delivery ratio and delay, for any number of message copies. Our conclusion is that such a Hybrid DTN-MANET approach offers a promising venue for the delivery of elastic data in mobile ad-hoc networks as it retains the resilience of a pure DTN protocol while significantly improving performance.Comment: 7 pages, 6 figure

    Performance evaluation of generic routing protocols in mobile ad hoc networks

    Get PDF
    Mobile Ad hoc Network or MANET in short is a self-configuring and infrastructure-less network of mobile nodes or devices that are connected wirelessly. There is no local base yet every device in a MANET is allowed to move autonomously in any pattern, consequently changing its connection to different devices much of the time. Each must act as a router and forward traffic. Each device or node participating in a MANET forwards data for other nodes, so the nodes forwarding data are dynamically determined on the basis of network connectivity. Ad hoc networks can use flooding for forwarding data. Mobile Ad-hoc networks generally have a routable systems network environments on top of the link layer. The decentralized nature of mobile ad hoc systems makes it suitable for a mixture of applications where local nodes can't be depended on and can enhance the versatility of networks in correlation from managed wireless networks. In my thesis, I’ve evaluated and implemented mobile ad hoc protocols in NS2 simulator and compared the routing protocols under different network parameters. The following protocols have been taken from three different categories:- i) Reactive Routing – DSR, AODV ii) Hybrid Routing – ZR

    Multimedia Content Distribution in Hybrid Wireless Networks using Weighted Clustering

    Get PDF
    Fixed infrastructured networks naturally support centralized approaches for group management and information provisioning. Contrary to infrastructured networks, in multi-hop ad-hoc networks each node acts as a router as well as sender and receiver. Some applications, however, requires hierarchical arrangements that-for practical reasons-has to be done locally and self-organized. An additional challenge is to deal with mobility that causes permanent network partitioning and re-organizations. Technically, these problems can be tackled by providing additional uplinks to a backbone network, which can be used to access resources in the Internet as well as to inter-link multiple ad-hoc network partitions, creating a hybrid wireless network. In this paper, we present a prototypically implemented hybrid wireless network system optimized for multimedia content distribution. To efficiently manage the ad-hoc communicating devices a weighted clustering algorithm is introduced. The proposed localized algorithm deals with mobility, but does not require geographical information or distances.Comment: 2nd ACM Workshop on Wireless Multimedia Networking and Performance Modeling 2006 (ISBN 1-59593-485

    Overview of Hybrid MANET-DTN Networking and its Potential for Emergency Response Operations

    Get PDF
    Communication networks for emergency response operations have to operate in harsh environments. As fixed infrastructures may be unavailable (e.g., they are destroyed or overloaded), mobile ad-hoc networks (MANETs) are a promising solution to establish communication for emergency response operations. However, networks for emergency responses may provide diverse connectivity characteristics which imposes some challenges, especially on routing. Routing protocols need to take transmission errors, node failures and even the partitioning of the network into account. Thus, there is a need for routing algorithms that provide mechanisms from Delay or Disruption Tolerant Networking (DTN) in order to cope with network disruptions but at the same time are as efficient as MANET routing schemes in order to preserve network resources. This paper reviews several hybrid MANET-DTN routing schemes that can be found in the literature. Additionally, the paper evaluates a realistic emergency response scenario and shows that MANET-DTN routing schemes have the potential to improve network performance as the resulting network is diverse in terms of connectivity. In particular, the network provides well-connected regions whereas other parts are only intermittently connected

    Research on Wireless Multi-hop Networks: Current State and Challenges

    Full text link
    Wireless multi-hop networks, in various forms and under various names, are being increasingly used in military and civilian applications. Studying connectivity and capacity of these networks is an important problem. The scaling behavior of connectivity and capacity when the network becomes sufficiently large is of particular interest. In this position paper, we briefly overview recent development and discuss research challenges and opportunities in the area, with a focus on the network connectivity.Comment: invited position paper to International Conference on Computing, Networking and Communications, Hawaii, USA, 201

    Internet connectivity for mobile Ad Hoc networks

    Get PDF
    Ad hoc networking allows portable devices to establish communication independent of a central infrastructure. However, the fact that there is no central infrastructure and that the devices can move randomly gives rise to various kind of problems, such as routing and security. In this thesis the problem of routing is considered. There are several ad hoc routing protocols, such as AODV, DSR, OLSR and ZRP, that propose solutions for routing within a mobile ad hoc network. However, since there is an interest in communication between not only mobile devices in an ad hoc network, but also between a mobile device in an ad hoc network and a fixed device in a fixed network (e.g. the Internet), the ad hoc routing protocols need to be modified. In this thesis the ad hoc routing protocol AODV is used and modified to examine the interconnection between a mobile adhoc network and the Internet. For this purpose Network Simulator 2, ns2, has been used. Moreover, three proposed approaches for gateway discovery are implemented and investigated. The goal of the thesis project is twofold: • To modify the source code of AODV in accordance with the Internet draft\Global connectivity for IPv6 Mobile Ad Hoc Networks " which presents a solution where AODV is used to provide Internet access to mobile nodes. • To implement and compare di®erent approaches for gateway discovery. In this thesis, three di®erent type of gateway discovery have been taken: • The proactive gateway discovery is initiated by the gateway itself. The gateway periodically broadcasts a gateway advertisement message which is transmitted after expiration of the gateways timer. The time between two consecutive advertisements must be chosen with care so that the network is not °ooded unnecessarily. All mobile devices residing in the gateways transmission range receive the advertisement and update information about gateway. After receiving advertisement, a mobile device just forward it broadcast it again. This process goes on within entire MANET. • In reactive gateway discovery a mobile device of MANET connects by gateway only when it is needed. For that the mobile device broadcasts request message to the ALL MANET GW MULTICAST address (the IP address for the group of all gateways in a mobile ad hoc network). Thus, only the gateways are addressed by this message and only they process it. Intermediate mobile nodes that receive the message just forward it by broadcasting it again up to gateway. • To minimize the disadvantages of proactive and reactive gateway discovery, the two approaches can be combined. This results is a hybrid gateway discovery. For mobile devices in a certain range around a gateway, proactive gateway discovery is used. Mobile devices residing outside this range use reactive gateway discovery to obtain information about the gateway. In comparing theses di®erent gateway discovery, three matrices are used. These are packet delivery ratio,average end-to-end delay and overhead. In case of proactive gateway discovery and hybrid gateway discovery, value of packet delivery ratio is larger than reactive gateway discovery. In case of proactive gateway discovery and hybrid gateway discovery, value of end to end delay is less than reactive gateway discovery. The overhead of proactive gateway discovery is greater than other two gateway discovery As for the average end-to-end delay, the proactive and hybrid methods perform slightly better than the reactive method. Concerning the routing overhead, when the advertisement interval is short the reactive method generates much less overhead than the proactive method, which in turn generates much less overhead than the hybrid method
    corecore