Wireless sensor networks (WSNs) serving in hostile environments are susceptible to multiple collocated failures due to explosives and natural calamities such as avalanches, landslides, etc., which can partition the network into disjoint segments. In such a scenario, federating the segments becomes essential for reestablishing communication among segments and resuming the WSN operation. Placing relays has been a popular strategy for forming a connected inter-segment topology. In this paper, we tackle the federation problem while considering constrained relay availability. We exploit the use of a limited number of mobile relays to provide intermittent inter-segment connectivity. We propose FLOWER, a novel algorithm for Federation with LOW inter-segment latency and Even Relay load. FLOWER groups the segments into clusters and forms a star inter-cluster topology where each cluster is served by a distinct mobile relay. A cluster at the center of the area serves as a hub to bound inter-segment communication delay. In addition, FLOWER opts to prolong the lifetime of the mobile relays by balancing the energy overhead due to travel and wireless communication. We validate its performance through extensive simulation experiments.

Multicast streams are the most popular traffic pattern in many applications of mobile ad-hoc networks (MANET). However, the mobility of nodes causes frequent changes to the network topology and thus efficient routing of multicast traffic becomes very challenging. The establishment of a core-mesh has been deemed as a very effective solution for these dynamic setups. The core-mesh acts as a backbone in order to avoid frequent route discovery. However maintaining the core-mesh imposes significant overhead that dominates the performance for large networks. This paper advocates a novel methodology that combines network clustering and mesh-based multicast routing. The Cluster-Mesh based Multicast Routing (CMMR) methodology forms a backbone using cluster-heads. This makes the backbone more stable against frequent node mobility and enables scalability by limiting the scope of the core maintenance. The paper mainly captures the performance advantage of CMMR over contemporary node-based core-mesh strategies. A mathematical model is developed to analyze the average performance of one of the contemporary core-mesh routing schemes and an implementation of the CMMR methodology using the same mesh formation algorithm. The numerical results demonstrate the advantage of CMMR.

Abstract The limited channel capacity and the varying propagation conditions of radio signals have motivated research for boosting the achievable throughput in wireless networks. Among the effective optimization strategies is to dynamically adjust the packet size either to better suit the channel conditions or to minimize the number of overhead bits in the individual packets. However, multi‐levels of security requirements impose constraints on the data mix in the packet payload and may diminish the gains achievable by contemporary packet‐size optimization schemes. This paper presents a novel bandwidth optimization algorithm for wireless data acquisition networks where strict confidentiality requirements and access restriction policies have to be observed. The algorithm exploits the classification of data in minimizing the number of packet transmissions as well as the overhead within the individual packets. The idea is to combine the transmission of packets based on the time sensitivity and security attributes of the data in the payload. The performance of the proposed algorithm is validated through mathematical analysis and through simulation. The simulation results confirm the effectiveness of the algorithm in boosting data throughput in the network. Copyright © 2010 John Wiley & Sons, Ltd.

In some applications of wireless sensor networks (WSNs), it may be necessary to link a number of disjoint segments in order to form a federated system. The segments can be simply distinct WSNs that operate autonomously or partitions of a single WSN that has suffered significant damage. Linking these segments may be subject to different intersegment quality of service (QoS) requirements. This paper presents an effective approach for federating these segments by populating the least number of relay nodes (RNs) such that the connectivity and QoS requirements are satisfied. Finding the optimal number and position of RNs is NP-hard and heuristics are thus pursued. The deployment area is modeled as a grid with equal-sized cells. A cost is assigned to each cell based on the residual capabilities of relays populated in it. The optimization problem is then mapped to finding the cell-based least-cost paths that collectively meet the QoS requirements. The performance of our approach is validated through extensive simulation experiments. We further demonstrate the beneficial aspects of the resulting topology with respect to degree of connectivity and fault resilience.

Abstract In this paper, we present a routing algorithm for a class of networks where a contemporaneous end‐to‐end path may not exist at the time of data transfer due to intermittent links. Several examples of such networks exist in the context of sensor networks, mobile ad hoc networks and delay tolerant networks. The proposed routing algorithms follow a priori routing similar to source routing. Link state changes are assumed to be known ahead of time, for instance, due to planned duty cycling resulting in scheduled connectivity. The basic idea behind the proposed routing algorithms is to modify the breadth first search (BFS) algorithm to take into account link state changes and find the quickest route between source and destination nodes. We introduce the idea of time‐varying storage domains where all nodes connected for a length of time act as a single storage unit by sharing the aggregated storage capacity of the nodes. This will help situations where storage is a limited resource. We evaluate the routing algorithm with and without storage domain in an extensive simulation. The delay performance of the proposed algorithms is conceptually the same as flooding‐based algorithms but without the penalty of multiple copies. More significantly, we show that the Quickest Storage Domain (Quickest SD) algorithm distributes the storage demand across many nodes in the network topology, enabling balanced load and higher network utilization. In fact, we show that for the same level of performance, we can actually cut the storage requirement in half using the Quickest SD algorithm. Copyright © 2009 John Wiley & Sons, Ltd.

Federating disjoint segments may be necessary in some applications of wireless sensor networks (WSNs). The segments can be simply distinct WSNs that operate autonomously or partitions of a single WSN that has suffered a significant damage. Linking these segments is subject to varying distances among segments which may be longer than twice the communication range of a relay node. In this work, we focus on designing an effective approach for federating these segments by populating the least number of relay nodes. The deployment area is modeled as a grid with equal-sized cells. The optimization problem is then mapped to selecting the fewest count of cells to populate relay nodes such that all segments are connected. Finding the optimal number and positions of relay nodes with respect to length between segments is NP-hard and heuristics are thus pursued. We propose a distributed Cell-based Optimized Relay node Placement (CORP) algorithm and explain the beneficial aspects of the resulting topology with respect to connectivity, and traffic balance. The performance of CORP is validated through extensive simulation experiments.

Recent years have witnessed a growing interest in the applications of wireless sensor networks (WSNs). In some of these applications, such as search and rescue and battlefield reconnaissance, a set of mobile nodes is deployed in order to collectively survey an area of interest and/or perform specific surveillance tasks. Such collaboration among the sensors requires internode interaction and thus maintaining network connectivity is critical to the effectiveness of WSNs. While connectivity can be provisioned at startup time and then sustained through careful coordination when nodes move, a sudden failure of a node poses a challenge since the network may get partitioned. This paper presents RIM; a distributed algorithm for Recovery through Inward Motion. RIM strives to efficiently restore the network connectivity after a node failure. Instead of performing a networkwide analysis to assess the impact of the node failure and orchestrate a course of action, RIM triggers a local recovery process by relocating the neighbors of the lost node. In addition to minimizing the messaging overhead, RIM opts to reduce the distance that the individual nodes have to travel during the recovery. The correctness of the RIM algorithm is proven and the incurred overhead is analyzed. The performance of RIM is validated through simulation experiments.

In some applications of wireless sensor networks (WSNs) it may be necessary to federate a number of disjoint segments. Linking these segments may be subject to varying inter-segment quality of service (QoS) requirements. This paper presents an effective approach for federating these segments. The main idea is to place relay nodes (RNs) in order to establish intersegment connectivity with the least number of RNs while meeting the desired QoS requirements. Finding the optimal number and position of RNs is shown to be NP-hard and heuristics are thus pursued. The deployment area is modeled as a grid with equal-sized cells. Each cell is evaluated based on the residual capabilities of RNs populated in the cell. The optimization problem is then mapped to finding the cell-based least cost paths that collectively meet the QoS requirements. The performance of the proposed approach is validated through simulation.

The effectiveness of wireless sensor networks (WSNs) deployed in search and rescue, battlefield reconnaissance, surveillance, and other applications depends on inter-node interaction and maintaining network connectivity. While connectivity can be provisioned at startup, then sustained through careful coordination when nodes move, the network can be partitioned if a node suddenly fails. This paper presents recovery through inward motion (RIM), a distributed algorithm to efficiently restore network connectivity after a node failure. Instead of performing a network-wide analysis to assess the impact of the node failure and set a course of action, RIM triggers a local recovery process by relocating the neighbors of the lost node. RIM minimizes messaging overhead and reduces the distance that individual nodes travel during the recovery. Simulations validate RIM's performance.

The topic of this paper is the algorithmic development of routing techniques for Delay Tolerant Networks (DTNs). Assuming a store and forward type of network transfers, our main objective in designing routing algorithms is to minimize the delay and maximize delivery subject to storage constraints on intermediate nodes connected by intermittent links. We present a novel modification to the breadth-first search algorithm to find the quickest route between a given source and any destination node in a delay-tolerant network. This is done without flooding the network - at any one time we maintain only one copy of the message in the network. We implement the proposed routing algorithm in NS2 and present an extensive performance analysis using metrics such as delivery ratio, incomplete transfers with no routes and dropped messages.