Improved group-based cooperative caching scheme for mobile ad hoc networks

Data caching is a popular technique that improves data accessibility in wired or wireless networks. However, in mobile ad hoc networks, improvement in access latency and cache hit ratio may diminish because of the mobility and limited cache space of mobile hosts (MHs). In this paper, an improved cooperative caching scheme called group-based cooperative caching (GCC) is proposed to generalize and enhance the performance of most group-based caching schemes. GCC allows MHs and their neighbors to form a group, and exchange a bitmap data directory periodically used for proposed algorithms, such as the process of data discovery, and cache placement and replacement. The goal is to reduce the access latency of data requests and efficiently use available caching space among MH groups. Two optimization techniques are also developed for GCC to reduce computation and communication overheads. The first technique compresses the directories using an aggregate bitmap. The second employs multi-point relays to develop a forwarding node selection scheme to reduce the number of broadcast messages inside the group. Our simulation results show that the optimized GCC yields better results than existing cooperative caching schemes in terms of cache hit ratio, access latency, and average hop count.     

GeoQuorums: implementing atomic memory in mobile ad hoc networks

We present a new approach, the GeoQuorums approach, for implementing atomic read/write shared memory in mobile ad hoc networks. Our approach is based on associating abstract atomic objects with certain geographic locations. We assume the existence of focal points, geographic areas that are normally “populated” by mobile nodes. For example, a focal point may be a road junction, a scenic observation point, or a water resource in the desert. Mobile nodes that happen to populate a focal point participate in implementing a shared atomic object, using a replicated state machine approach. These objects, which we call focal point objects, are prone to occasional failures when the corresponding geographic areas are depopulated. The GeoQuorums algorithm uses the fault-prone focal point objects to implement atomic read/write operations on a fault-tolerant virtual shared object. The GeoQuorums algorithm uses a quorum-based strategy in which each quorum consists of a set of focal point objects. The quorums are used to maintain the consistency of the shared memory and to tolerate limited failures of the focal point objects, which may be caused by depopulation of the corresponding geographic areas. We present a mechanism for changing the set of quorums on the fly, thus improving efficiency. Overall, the new GeoQuorums algorithm efficiently implements read and write operations in a highly dynamic, mobile network.     

Integrated location management and location-aided routing system for mobile ad hoc networks

We present an integrated location management and location-aided routing system for mobile ad hoc network (MANET) which organizes the MANET into a two-level routing hierarchy with the help of Voronoi diagrams. The location information of mobile nodes in a Voronoi zone is summarized using bloom filters and distributed among the location servers in the zones. In the integrated system, the destination's location is learned during routing in the overlay network of the hierarchy. Theoretical analysis and simulation results show that the proposed system reduces the routing time by about 25% over traditional location-aided routing techniques for transaction-type traffic while incurring only small management overhead and low storage requirement.     

Triangle-based routing for mobile ad hoc networks

Routing protocols for Mobile ad hoc networks (MANETs) have been studied extensively in the past decade. Routing protocols for MANETs can be broadly classified as reactive (on-demand), proactive, hybrid and position-based. Reactive routing protocols are attractive because a route between a source and a destination is established only when it is needed. Such protocols, unlike proactive protocols, do not have high overhead for route maintenance and are especially suitable for networks in which not all nodes communicate frequently. One problem with existing reactive routing protocols is the propagation of redundant route request messages during route discovery. In this paper, we present a low-overhead reactive routing protocol which reduces propagation of redundant route request messages. We also compare its performance with the well-known reactive routing protocol AODV.     

Neighborhood tracking for mobile ad hoc networks

In mobile ad hoc networks (MANETs), node mobility causes network topologies to change dynamically over time, which complicates such important tasks as broadcasting and routing. In a typical efficient localized approach, each node makes forwarding decisions based on a neighborhood local view constructed simply by collecting received “Hello” messages. That kind of neighborhood local view can become outdated and inconsistent, which induces a low-coverage problem for efficient broadcasting tasks and a low-delivery ratio problem for efficient routing tasks. In this paper, we propose a neighborhood tracking scheme to guarantee the accuracy of forwarding decisions. Based on historical location information, nodes predict the positions of neighbors when making a forwarding decision, and then construct an updated and consistent neighborhood local view to help derive more precise forwarding decisions. The inaccuracy factors of our scheme are also discussed and an accessory method is provided for possible usage. Simulation results illustrate the accuracy of our proposed tracking scheme. To verify the effectiveness of our scheme, we apply it to existing efficient broadcast algorithms. Simulation results indicate that our neighborhood tracking scheme can improve the protocols coverage ratio greatly.     

A scalable publish/subscribe system for large mobile ad hoc networks

Since nodes that compose mobile ad hoc networks (MANETs) does not have any prior knowledge about other nodes in many cases, the publish/subscribe communication paradigm that has the decoupling and asynchrony properties can be useful to share information between nodes. Existing publish/subscribe services for MANETs can be categorized into document flooding (DF), destination-based routing (DBR), and content-based routing (CBR). Although those approaches may work well when the size of network is small, all of them suffer from the performance decline as the size of the network increases. In this paper, we compare those approaches, and then propose a scalable publish/subscribe communication scheme in large MANETs by combining DF and CBR hierarchically. Our approach is to cluster all nodes in networks and to exploit CBR and DF for the intra- and inter-cluster communication, respectively. By using this approach, we can effectively utilize benefits of both approaches. Then, we present performance evaluation results which validate our idea with respect to system performance and scalability.     

Cost-effective mobile ad hoc networks management

As there are more and more mobile devices in use, different mobile networking models such as ad hoc or mesh are attracting a large research interest. Self-organizing mobile ad hoc networks (MANET) allow devices to share their services and resources without any central administration or Internet support. In this respect they can become the backbone of the wireless grid or the gateway to existing grids. To achieve these goals, MANET management must be as effective as that of wired networks. This is, however, a challenging task due to network features like mobility, heterogeneity, limited resources of hosts and feeble communication. This paper presents a set of simple, cost-effective and resilient procedures for the basic tasks of MANET creation and management.     

Model checking mobile ad hoc networks

Modeling arbitrary connectivity changes within mobile ad hoc networks (MANETs) makes application of automated formal verification challenging. We use constrained labeled transition systems as a semantic model to represent mobility. To model check MANET protocols with respect to the underlying topology and connectivity changes, we introduce a branching-time temporal logic. The path quantifiers are parameterized by multi-hop constraints over topologies, to discriminate the paths over which the temporal behavior should be investigated; the paths that violate the multi-hop constraints are not considered. A model checking algorithm is presented to verify MANETs that allow arbitrary mobility, under the assumption of reliable communication. It is applied to analyze a leader election protocol.     

Robust self-keying mobile ad hoc networks

Pairwise key establishment in mobile ad hoc networks allows any pair of nodes to agree upon a shared key. This is an important security service needed to secure routing protocols, and in general to facilitate secure communication among the nodes of the network.We present two self-keying mechanisms for pairwise key establishment in mobile ad hoc networks which do not require any centralized support. The mechanisms are built using the well-known technique of threshold secret sharing, and are robust and secure against a collusion of up to a certain number of nodes. We evaluate and compare the performance of both the mechanisms in terms of the node admission and pairwise key establishment.     

Contention-aware data caching in wireless multi-hop ad hoc networks

This paper studies a challenging problem of cache placement in wireless multi-hop ad hoc networks. More specifically, we study how to achieve an optimal tradeoff between total access delay and caching overheads, by properly selecting a subset of wireless nodes as cache nodes when the network topology changes. We assume a data source updates a data item to be accessed by other client nodes. Most of the existing cache placement algorithms use hop counts to measure the total cost of a caching system, but hop delay in wireless networks varies much due to the contentions among these nodes and the traffic load on each link. Therefore, we evaluate the per-hop delay for each link according to the contentions detected by a wireless node from the MAC layer. We propose two heuristic cache placement algorithms, named Centralized Contention-aware Caching Algorithm (CCCA) and Distributed Contention-aware Caching Algorithm (DCCA), both of which detect the variation of contentions and the change of the traffic flows, in order to evaluate the benefit of selecting a node as a cache node. We also apply a TTL-based cache consistency strategy to maintain the delta consistency among all the cache nodes. Simulation results show that the proposed algorithms achieve better performance than other alternative ones in terms of average query delay, caching overheads, and query success ratio.     

Adaptive routing protocol for mobile ad hoc networks

Artificial immune systems (AIS) are used for solving complex optimization problems and can be applied to the detection of misbehaviors, such as a fault tolerant. We present novel techniques for the routing optimization from the perspective of the artificial immunology theory. We discussed the bioinspired protocol AntOR and analyze its new enhancements. This ACO protocol based on swarm intelligence takes into account the behavior of the ants at the time of obtaining the food. In the simulation results we compare it with the reactive protocol AODV observing how our proposal improves it according to Jitter, the delivered data packet ratio, throughput and overhead in number of packets metrics.     

Hash caching mechanism in source-based routing for wireless ad hoc networks

In mobile ad hoc network (MANET), on-demand routing protocols are proposed for establishing a route in a distributed manner only when a source host originates a data packet addressed to the destination host. In source-based routing (SBR) protocols, route discovery usually raises a large number of request packets for exploring the current state of the network, but it also performs the collection of useful information for future routing decisions. How to store and manage this collected information in the limited size of cache in order to improve routing performance is still an open issue in the development of an SBR scheme. This paper proposes a novel hash caching mechanism and distributed hashing routing methods to store, utilize, and manage the cached routes in order to improve cache capacity, routing performance, and network throughput. The experimental results indicate that the proposed mechanism offers high cache capacity, efficient route discovery, and good throughput for the MANET.     

Privacy addressing and autoconfiguration for mobile ad hoc networks

Allowing truly spontaneous and infrastructureless networking, mobile ad hoc networks (MANETs) are the future of wireless networks. However, most autoconfiguration proposals for MANETs lack privacy support, namely anonymity or pseudonymity and unlinkability aspects, which has become important considerations in many practical applications. This paper presents a novel privacy extension approach (PEA) for MANETs, which prevents eavesdroppers from identifying a particular mobile node by its address. In addition to privacy concerns, our scheme also brings some performance benefits, e.g., reducing the possibility of address conflict when the merging of separately configured networks occurs.     

Markovian-based traffic modeling for mobile ad hoc networks

Mobile ad hoc networks (MANETs) show very significant difference with respect to other computer networks due to the presence of extremely large packet loss bursts. The development of protocols for mobile ad hoc networks, especially multimedia protocols, require extensive evaluation either through simulation or real-life tests. Such testing consumes a great amount of resources both in terms of time and trace file sizes. Therefore, finding efficient means of reducing the amount of data that is stored and processed is quite important to accelerate the evaluation of different audio/video streaming applications. If, moreover, we are able to model the loss pattern experienced, we can further accelerate the evaluation process.In this work we propose two models based on hidden Markov chains that are able to grasp both packet arrivals and packet loss patterns in MANETs. A simpler two-state model is proposed to model losses when proactive routing protocols are used, while a more complex three-state model is proposed for reactive routing protocols. We also introduce a new set for packet loss pattern measurements that can be of interest for the evaluation of audio/video streaming applications.Experimental results show that the proposed models can adequately reproduce extremely long packet loss patterns, typical of MANET environments, with a high degree of accuracy. Overall, we find that the proposed models are able to significantly reduce both the simulation time and the trace file sizes required.     

Reduction of the broadcast redundancy by location awareness in mobile ad hoc networks

In this paper, a reachability-guaranteed approach for reducing broadcast storms in MANET is proposed. The approach is based on location awareness of each node, which means each node in the network needs to equip the positioning device like GPS and exchanges location information in the HELLO message with its neighbors. Three mechanisms are included in the proposed approach: Relay Set (RS), Neighbor Coverage (NC), and Transmission Order (TO). RS is a sender-based mechanism in which the sending node of the broadcast message determines the relay set of its neighbors for rebroadcast according to the radio coverage of the neighbors. The idea of the received-based NC is: a node receiving a broadcast message does not have to rebroadcast the message if all its neighbors have received the same message. TO mechanism requires a farther neighbor node away from the sending node to rebroadcast the message earlier than closer nodes so that a closer node may have more chances to save the rebroadcast. Simulation results have shown that the proposed approach ‘RS+NC+TO’ has a better performance than existing solutions like threshold-based schemes and angle-based scheme in terms of 100% reachability, more saved rebroadcast, and shorter average latency.     

Integrating mobile IP with ad hoc networks

Extending traditional IEEE 802.11-based access points to incorporate the flexibility of mobile ad hoc networks would help make the dream of ubiquitous broadband wireless access a reality. The authors discuss several issues related to integrating the mobile Internet protocol with Manets.     

Group communications in mobile ad hoc networks

Efficient support of group communications is critical for most ad hoc network applications. However, manet group communications issues differ from those in wired environments because the wireless communications medium has variable and unpredictable characteristics, and the signal strength and propagation fluctuate with respect to time and environment. We provide an overview of group communications issues such as protocol design, state maintenance, and performance. We also discuss representative protocols and examine related issues such as reliability, power conservation, quality of service, security, and areas requiring additional research.     

移动自组网的动态编址问题

作为实现移动自组网自动配置的一个关键问题,综述了节点地址的自动配置的最新进展,描述了设计移动自组网动态地址配置协议所面临的问题,对该问题研究开展以来所提出的各种主要方法和协议进行了详细对比、分析和分类阐述,为进一步的研究提出了新的建议。     

Routing and security in mobile ad hoc networks

Mobile ad hoc networks remove the dependence on a fixed network infrastructure by treating every available mobile node as an intermediate switch, thereby extending the range of mobile nodes well beyond that of their base transceivers. We present four manet routing algorithms along with a hybrid approach, discuss their advantages and disadvantages, and describe security problems inherent in such networks.