Presence Of Link Failures Research Articles

Improving Data Delivery in Unreliable Networks Using Network Coding and Ant-Colony Optimization

Wireless Sensor Networks (WSNs) comprise interconnected wireless nodes that receive and transmit data across applications and platforms. This paper addressed the problem of link failures in WSNs that potentially could lead to the loss of data packets while still in transit. This was achieved through the use of network coding which is known to address capacity bottleneck problems in WSNs. In particular, a technique called Ant Agent-Assisted Network Coding (AAANC) is proposed that employs the ant colony optimization technique in addition to network coding operations. The main aim of AAANC is to facilitate the successful delivery and decoding of coded data packets in the presence of link failures. AAANC employs a packet route selection technique that is inspired by the social behavior of natural ants. For natural ants, a strong pheromone trail along a path indicates a promising route to a food source, and this is analogous to a reliable communication link for routing data packets in this paper. Through simulations, AAANC was compared to diagonal pseudorandom network coding (DNC) and triangular pseudorandom network coding (TNC), and it proved to have a superior performance in terms of packet delivery ratio and number of decoded packets. Significant performance gain can be achieved if AAANC algorithm is made to dynamically adapt the ant colony and network coding parameters in response to traffic changes.

Distributed Kalman Filtering Over Sensor Networks With Unknown Random Link Failures

In this letter we consider the distributed consensus-based filtering problem for linear time-invariant systems over sensor networks subject to random link failures when the failure sequence is not known at the receiving side. We assume that the information exchanged, traveling along the channel, is corrupted by a noise and hence, it is no more possible to discriminate with certainty if a link failure has occurred. Therefore, in order to process the only significant information, we endow each sensor with detectors which decide on the presence of link failures. At each sensor the proposed approach consists of three steps: (1) failure detection; (2) local data aggregation; and (3) Kalman consensus filtering. Numerical examples show the effectiveness of this method.

Mathematical Analysis of Trust Computing Algorithms

Abstract To overcome a frequent occurrence of routing loops due to communication link failure and to provide an ensured packet delivery among the Vehicular Ad-hoc Networks (VANET), an Optimized Node Selection Routing Protocol (ONSRP) of VANET has been implemented using a Trust Computing Algorithm. Basically, the time efficiency indicates how fast the algorithm runs. In this paper, the Trust Computing algorithm has been analyzed mathematically to find the time complexity of the algorithm currently chosen and hence achieved trusted communication and high packet delivery ratio of data transmission among the Vehicular Adhoc Networks. We could confirm that the ONSRP is optimal by comparing it to the Scalable Hybrid Routing (SHR) communication overhead and packet delivery ratio of the network from both analysis and simulation in the presence of link failures.

A Dynamic Random Graph Model for Diameter-Constrained Topologies in Networked Systems

Random graphs have been widely investigated in the literature because of their relevance to many scientific domains. In this brief, the attention is focused on diameter-constrained random graphs, which are useful in analyzing unstructured overlays for delay-bounded network applications and systems. To this end, a general process of arrivals is considered, which describes the sequence of vertex couples (i.e., node couples) among which a path composed of no more than $D$ edges (i.e., links) has to be established. Accordingly, a topology formation mechanism $M$ is formulated, expressing the rules that drive the addition of new edges, obeying to the constraint on the maximum diameter $D$ . Third, using graph-theoretic arguments, an original discrete-time model is proposed, which describes the evolution of the average network degree (i.e., the average number of edges per node) subject to $M$ and $D$ . Fourth, the model is successfully validated using computer simulations in a wide range of scenarios (with up to $2^{16}$ nodes). Finally, concrete examples are provided to illustrate useful applications of the proposed approach, also in the presence of link failures.

Nullspace-based stopping conditions for network-coded transmissions in DTNs

In a challenged network environment, where end-to-end connectivity may be a rare occurrence, delay-tolerant routing protocols must strike a balance between the increased robustness and reliability that comes with message replication and the resulting high bandwidth and storage overhead. Network coded routing, in which a node combines messages from different sources, has been shown to increase reliability in the presence of link failures with small additional overhead. A drawback of network coded routing is the lack of a natural stopping condition to control the dissemination of data. We describe an enhanced coding router that uses the mathematical structure of the orthogonal complement, or nullspace, as an improved stopping condition to eliminate redundant transmissions, and an additional technique to balance multiple coded data flows. These changes are incorporated into the DTN2 Reference Implementation and evaluated in two types of experiments. In a simple data-mule scenario, our EBR router comes very close to perfect efficiency. In a more complicated scenario with segmented communities and occasional nodes moving between them, our solutions show a drastic improvement in delivery rates.

Plato: a genetic algorithm approach to run-time reconfiguration in autonomic computing systems

Increasingly, applications need to be able to self-reconfigure in response to changing requirements and environmental conditions. Autonomic computing has been proposed as a means for automating software maintenance tasks. As the complexity of adaptive and autonomic systems grows, designing and managing the set of reconfiguration rules becomes increasingly challenging and may produce inconsistencies. This paper proposes an approach to leverage genetic algorithms in the decision-making process of an autonomic system. This approach enables a system to dynamically evolve target reconfigurations at run time that balance tradeoffs between functional and non-functional requirements in response to changing requirements and environmental conditions. A key feature of this approach is incorporating system and environmental monitoring information into the genetic algorithm such that specific changes in the environment automatically drive the evolutionary process towards new viable solutions. We have applied this genetic-algorithm based approach to the dynamic reconfiguration of a collection of remote data mirrors, demonstrating an effective decision-making method for diffusing data and minimizing operational costs while maximizing data reliability and network performance, even in the presence of link failures.

A game theoretic framework for the robust railway transit network design problem

This paper proposes a game theoretic framework for the problem of designing an uncapacitated railway transit network in the presence of link failures and a competing mode. It is assumed that when a link fails, another path or another transportation mode is provided to transport passengers between the endpoints of the affected link. The goal is to build a network that optimizes a certain utility function when failures occur. The problem is posed as a non-cooperative two-player zero-sum game with perfect information. The saddle points of the corresponding mixed enlarged game yield robust network designs.

Optimal placements of replicas in a ring network with majority voting protocol

In a distributed database system, data replicas are placed at different locations to achieve high data availability in the presence of link failures. With a majority voting protocol, a location survives for read/write operations if and only if it is accessible to more than half of the replicas. The problem is to find out the optimal placements for a given number of data replicas in a ring network. When the number of replicas is odd, it was conjectured by Hu et al. [X.-D. Hu, X.-H. Jia, D.-Z. Du, D.-Y. Li, H.-J. Huang, Placement of data replicas for optimal data availability in ring networks, J. Parallel Distrib. Comput., 61 (2001) 1412–1424] that every uniform placement is optimal, which is proved by Shekhar and Wu later. However, when the number of replicas is even, it was pointed out by Hu et al. that uniform placements are not optimal and the optimal placement problem may be very complicated. In this paper, we study the optimal placement problem in a ring network with majority voting protocol and an even number of replicas, and give a complete characterization of optimal placements when the number of replicas is not too large compared with the number of locations.

A new approach for designing fault-tolerant WDM networks

In recent years, path protection has emerged as a widely accepted technique for designing survivable WDM networks. This approach is attractive, since it is able to provide bandwidth guarantees in the presence of link failures. However, it requires allocating resources for backup lightpaths, which remain idle under normal fault-free conditions. In this paper, we introduce a new approach for designing fault-tolerant WDM networks, based on the concept of survivable routing. Survivable routing of a logical topology ensures that the lightpaths are routed in such a way that a single link failure does not disconnect the network. When a topology is generated using our approach, it is guaranteed to have a survivable routing. We further ensure that the logical topology is able to handle the entire traffic demand after any single link failure. We first present an ILP that optimally designs a survivable logical topology, and then propose a heuristic for larger networks. Experimental results demonstrate that this new approach is able to provide guaranteed bandwidth, and is much more efficient in terms of resource utilization, compared to both dedicated and shared path protection.

Optimal placement of data replicas in distributed database with majority voting protocol

In a distributed database system, data replicas are placed at different locations of a network to achieve the high data availability in presence of link failure. Optimal placements of data replicas have been studied extensively in the literature for various protocol. In this paper, we present a sufficient and necessary condition for optimality of a placement of odd number of data replicas in a ring network with majority voting protocol. As a corollary, we give a proof of a recent conjecture of Hu et al. (manuscript, 1999). Moreover, we also give a simple algorithm to find optimal placements in tree network with majority voting protocol.

Distributed decision fusion in the presence of link failures

The problem of optimal data fusion involving detector unit communication link failures is considered. Two strategies for decision making in presence of link failures are examined and an optimal decision making scheme in the sense of the Neyman-Pearson (N-P) test is proposed. The performance of q+1 reliable links versus q reliable links are examined theoretically, as well as, numerically using the receiver operating characteristics (ROCs).

Leader election in the presence of link failures

We study the problem of leader election in the presence of intermittent link failures. We assume that up to N/2-1 links incident on each node may fail during the execution of the protocol. We present a message optimal algorithm with message complexity O(N/sup 2/).

On fault-tolerant embedding of Hamiltonian circuits in line digraph interconnection networks

Interconnection networks based on directed line graphs have a nice property: an Euler tour in the digraph G translates to a Hamiltonian circuit in the line digraph L( G). Moreover, the existence of a Hamiltonian circuit in L( G) implies that G must be Eulerian. While Hamiltonian circuits are hard to find in the presence of link failures, the equivalent Euler tours are relatively easy to find in the presence of forbidden link pairs (corresponding to the link failures in L( G)). We explore this idea and present necessary and sufficient conditions for the existence of fault-free Euler tour in a digraph. We also present an algorithm to find such an Euler tour when it exists.

On the complexity of global computation in the presence of link failures: the general case

This paper presents Ω(m log n) and Ω(mn) messages lower bounds on the problem of computing a global sensitive function in bidirectional networks with link failures (i.e., dynamically changing topology), where n and m are the total number of nodes and links in the network. The Ω(mlogn) lower bound is under the assumption that n is a-priori known to the nodes, while the second bound is for the case in which such knowledge is not available. A global sensitive function of n variables is a function that may not be computed without the knowledge of the values of all the n variables (e.g. maximum, sum, etc). Thus, computing such a function at one node of a distributed network requires this node to communicate with every other node in the network. Though lower bounds higher than Ω(m) messages are known for this problem in the context of link failures, none holds for dense bidirectional networks. Moreover, we are not aware of any other non-trivial lower bound higher than Ω(m) for dense bidirectional networks.

On the complexity of computation in the presence of link failures: the case of a ring

We investigate the message complexity of distributed computations on rings of asynchronous processors. In such computations, each processor has an initial local value and the task is to compute some predetermined function of all local values. Our work deviates from previous works concerning the complexity of ring computations in that we consider the effect of link failures. A link is said to fail if some message sent through it never reaches its destination. We show that the message complexity of any function, which is "sensitive to all its inputs", is Θ(n log n) when n, the number of processors, is a-priori known; and is Θ(n2) when n is not known. Interestingly, these tight bounds do not depend on whether the identity of a leader is a-priori known before the computation starts. These results stand in sharp contrast to the situation in asynchronous rings with no link failures, where the message complexity is affected by the a-priori knowledge of a leader but is not affected by the knowledge of n.