Lewis M. Mackenzie

Performance Analysis of Adjusted Probabilistic Broadcasting in Mobile Ad Hoc Networks

Broadcasting in Mobile Ad Hoc Networks (MANETs) is a fundamental data dissemination mechanism with a number of important applications in, e.g., route discovery, address resolution. However, broadcasting induces what is known as the “broadcast storm problem” which causes severe degradation in network performance due to excessive redundant retransmission, collision, and contention. Broadcasting in MANETs has traditionally been based on flooding, which simply swamps the network with large number of rebroadcast messages in order to reach all network nodes. Although probabilistic flooding has been one of the earliest suggested schemes to broadcasting, there has not been so far any attempt to analyse its performance behaviour in a MANET environment. In an effort to fill this gap, this paper investigates using extensive ns-2 simulations the effects of a number of important system parameters in a typical MANET, including node speed, pause time, traffic load, and node density on the performance of probabilistic flooding. The results reveal that most of these parameters have a critical impact on the reachability and the number of saved rebroadcast messages achieved by probabilistic flooding.

An accurate analytical model of adaptive wormhole routing in k -ary n -cubes interconnection networks

Abstract Many fully adaptive algorithms have been proposed in the literature over the past decade. The performance characteristics of most of these algorithms have been analysed by means of software simulation only. This paper proposes an analytical model to predict message latency in wormhole-routed k-ary n-cubes with fully adaptive routing. The analysis focuses Duato’s fully adaptive routing algorithm [IEEE Trans. Parall. Distrib. Syst. 4 (2) (1993) 320], which is widely accepted as the most general algorithm for achieving adaptivity in wormhole-routed networks while allowing for an efficient router implementation. The proposed model is general in that it exhibits a good degree of accuracy for various network sizes and under different operating conditions.

Analytical modeling of wormhole-routed k-ary n-cubes in the presence of hot-spot traffic

Several analytical models of fully adaptive routing have recently been proposed for wormhole-routed k-ary n-cubes under the uniform traffic pattern. However, there has been hardly any model reported yet that deals with other important nonuniform traffic patterns, such as hot-spots. As a result, most studies have resorted to simulation when evaluating the performance merits of adaptive routing. In an effort to fill this gap, this paper describes the first analytical model of fully adaptive routing in k-ary n-cubes in the presence of hot-spot traffic. Results from simulation show close agreement with those predicted by the model.

An efficient counter-based broadcast scheme for mobile ad hoc networks

In mobile ad hoc networks (MANETs), broadcasting plays a fundamental role, diffusing a message from a given source node to all the other nodes in the network. Flooding is the simplest and commonly used mechanism for broadcasting in MANETs, where each node retransmits every uniquely received message exactly once. Despite its simplicity, it however generates redundant rebroadcast messages which results in high contention and collision in the network, a phenomenon referred to as broadcast storm problem. Pure probabilistic approaches have been proposed to mitigate this problem inherent with flooding, where mobile nodes rebroadcast a message with a probability p which can be fixed or computed based on the local density. However, these approaches reduce the number of rebroadcasts at the expense of reachability. On the other hand, counter-based approaches inhibit a node from broadcasting a packet based on the number of copies of the broadcast packet received by the node within a random access delay time. These schemes achieve better throughput and reachability, but suffer from relatively longer delay. In this paper, we propose an efficient broadcasting scheme that combines the advantages of pure probabilistic and counter-based schemes to yield a significant performance improvement. Simulation results reveal that the new scheme achieves superior performance in terms of saved-rebroadcast, reachability and latency.

Analysis of fully adaptive wormhole routing in tori

Abstract A model of adaptive routing in the hypercube has recently been proposed (Y. Boura, C.R. Das, T.M. Jacob, A performance model for adaptive routing in hypercubes, in: Proceedings of the International Workshop on Parallel Processing, 1994, pp. 11–16). Modelling adaptive routing in a high-radix k -ary n -cube, e.g., the torus, is more complicated than in the hypercube since a message in the former may cross more than one channel along a given dimension. This paper proposes a queuing model of adaptive routing in the torus. The validity of the model is demonstrated by comparing analytical results with those obtained through simulations.

Probabilistic counter-based route discovery for mobile ad hoc networks

Conventional on-demand route discovery for ad hoc routing protocols extensively use simple flooding, which could potentially lead to high channel contention, causing redundant retransmissions and thus excessive packet collisions in the network. This phenomenon has been shown to greatly increase the network communication overhead and end to end delay. This paper proposes a new probabilistic counter-based method that can significantly reduce the number of RREQ packets transmitted during route discovery operation. Our simulation results reveal that equipping AODV routing protocol with the proposed probabilistic counter-based route discovery method can result in significant performance improvements in terms of routing overhead, MAC collisions and end-to-end delay while still achieving a good throughput.

Improving route discovery in on-demand routing protocols using local topology information in MANETs

Most existing routing protocols proposed for MANETs use flooding as a broadcast technique for the propagation of network control packets; a particular example of this is the dissemination of route requests (RREQs), which facilitate route discovery. In flooding, each mobile node rebroadcasts received packets, which, in this manner, are propagated network-wide with considerable overhead. This paper improves on the performance of existing routing protocols by reducing the communication overhead incurred during the route discovery process by implementing a new broadcast algorithm called the adjusted probabilistic flooding on the Ad-Hoc on Demand Distance Vector (AODV) protocol. AODV [3] is a well-known and widely studied algorithm which has been shown over the past few years to maintain an overall lower routing overhead compared to traditional proactive schemes, even though it uses flooding to propagate RREQs. Our results, as presented in this paper, reveal that equipping AODV with fixed and adjusted probabilistic flooding, instead, helps reduce the overhead of the route discovery process whilst maintaining comparable performance levels in terms of saved rebroadcasts and reachability as achieved by conventional AODV\@. Moreover, the results indicate that the adjusted probabilistic technique results in better performance compared to the fixed one for both of these metrics

Adjusted probabilistic route discovery in mobile ad hoc networks

Conventional on-demand route discovery methods in mobile ad hoc networks (MANET) employ simple flooding method, where a mobile node blindly rebroadcasts received route request (RREQ) packets until a route to a particular destination is established. This can potentially lead to high channel contention, causing redundant retransmissions and thus excessive packet collisions in the network. This paper proposed two new probabilistic methods that can significantly reduce the number of RREQ packets transmitted during route discovery operation. Our simulation analysis reveals that equipping AODV with an appropriate probabilistic route discovery method can result in significant performance improvements in terms of routing overhead, MAC collisions and end-to-end delay while still achieving a good throughput when compared with the traditional AODV.

Non-contiguous processor allocation strategy for 2D mesh connected multicomputers based on sub-meshes available for allocation

Contiguous allocation of parallel jobs usually suffers from the degrading effects of fragmentation as it requires that the allocated processors be contiguous and has the same topology as the network topology connecting these processors. In non-contiguous allocation, a job can execute on multiple disjoint smaller sub-meshes rather than always waiting until a single sub-mesh of the requested size is available. Lifting the contiguity condition in non-contiguous allocation is expected to reduce processor fragmentation and increase processor utilization. However, the communication overhead is increased because the distances traversed by messages can be longer. The extra communication overhead depends on how the allocation request is partitioned and allocated to free sub-meshes. In this paper, a new noncontiguous processor allocation strategy, referred to as greedy-available-busy-list, is suggested for the 2D mesh network, and is compared using simulation against the well-known non-contiguous and contiguous allocation strategies. To show the performance improved by proposed strategy, we conducted simulation runs under the assumption of wormhole routing and all-to-all communication pattern. The results show that the proposed strategy can reduce the communication overhead and improve performance substantially in terms of turnaround times of jobs and finish times

Improving the Performance of Counter-Based Broadcast Scheme for Mobile AD HOC Networks

Flooding is the simplest and most commonly used mechanism for broadcasting in mobile ad hoc networks (MANETs), where each node retransmits every uniquely received message exactly once. Despite its simplicity, it can result in high redundancy, contention and collision, a phenomenon referred to as the broadcast storm problem. In this paper, we propose an enhanced counter-based scheme to mitigate this problem by incorporating probability concept into counter-based scheme. We evaluate the performance of our scheme by comparing it with flooding, fixed probability and counter-based scheme. The simulation results reveal that the new scheme achieves superior performance in terms of both saved rebroadcast and end to end delay, and reachability comparable to flooding in medium and dense networks.