Janelle J. Harms

Performance study of a multipath routing method for wireless mobile ad hoc networks

A Mobile Ad hoc NETwork (MANET) is a collection of wireless mobile computers forming a temporary network without any existing wire line infrastructure. Due to the dynamic nature of the network topology and the resource constraints, routing in MANETs is a challenging task. Multipath routing can increase end-to-end throughput and provide load balancing in wired networks. However, its advantage is not obvious in MANETs because the traffic along the multiple paths may interfere with each other . In addition, without accurate knowledge of topology, finding multiple disjoint paths is difficult. We propose an on-demand method to efficiently search for multiple node-disjoint paths and present the criteria for selecting the multiple paths. We also perform a simulation study on the proposed method. The purpose of this paper is to present the advantages as well as some difficulties of deploying multipath routing in MANETs.

Load-sensitive routing for mobile ad hoc networks

A mobile ad hoc network (MANET) is a collection of wireless mobile computers forming a temporary network with no existing wired infrastructure. Due to the dynamic nature of network topology and the resource constraints, routing in MANETs is a challenging task. Distributing the routing tasks fairly has eminent advantages, such as reducing the possibility of power depletion and queuing delay in the hosts with heavy duties. However, most current routing protocols for MANETs do not take load balancing into account. In this paper, we propose a load-sensitive on-demand routing approach, which utilizes the network load information as the main route selection criterion. We perform a simulation study on the proposed routing protocol. Compared with the dynamic source routing (DSR), our protocol shows better performance in terms of packet delivery ratio and average end-to-end delay. Further, with low mobility, these benefits are gained without an increase in the control overhead.

Resource management with virtual paths in ATM networks

A virtual path connection (VPC) is a labelled path which can be used to transport a bundle of virtual channel connections (VCCs) and to manage the resources used by these connections. The virtual network is organized as a collection of VPCs which form a VPC, or logical, overlay network. If the VPCs are permanent or semi-permanent and have reserved capacity, establishing new VCCs requires simple connection admission decisions at the VPC terminators of existing VPCs. This would enable faster connection establishment since transit nodes are not involved in the connection setup. The virtual path concept also allows the possibility of segregating traffic types according to quality of service requirements. However, the extent to which VPC provisioning is able to improve network efficiency is dependent on the resource management decisions that determine the VPC topology and capacity allocations. The article surveys resource management using virtual paths in an ATM network. Of interest are techniques which modify the VPC topology and capacity assignments in order to adapt to changing traffic conditions and possible network failures. The resource management activities employed to facilitate such adaptation can be categorized by the timescale on which they operate. On the shortest timescale are strategies for dynamically making minor changes to the VPC topology or capacity assignments. On a somewhat longer timescale are strategies for making more widespread modifications to the VPC overlay network. This would be appropriate for traffic changes based on time of day and for recovering from network failures. Finally, on an even longer timescale, strategies may be employed to design a general VPC overlay network, to be used at startup or after major network upgrades. Solutions to VPC resource management for each of these timescales are discussed.

Distributed classification of acoustic targets in wireless audio-sensor networks

Target tracking is an important application for wireless sensor networks. One important aspect of tracking is target classification. Classification helps in selecting particular target(s) of interest. In this paper, we address the problem of classification of moving ground vehicles. The basis of classification are the audible signals produced by these vehicles. We present a distributed framework to classify vehicles based on features extracted from acoustic signals of vehicles. The main features used in our study are based on FFT (fast Fourier transform) and PSD (power spectral density). We propose three distributed algorithms for classification that are based on the k-nearest neighbor (k-NN) classification method. An experimental study has been conducted using real acoustic signals of different vehicles recorded in the city of Edmonton. We compare our proposed algorithms with a naive distributed implementation of the k-NN algorithm. Performance results reveal that our proposed algorithms are energy efficient, and thus suitable for sensor network deployment.

Optimal Traffic-Oblivious Energy-Aware Routing for Multihop Wireless Networks

Energy efficiency is an important issue in multihop wireless networks with energy concerns. Usually it is achieved with accurate knowledge of the traffic pattern and/or the current network information such as the remaining energy level. We investigate the problem of designing a routing scheme to minimize the maximum energy utilization of a multihop wireless network with weak assumption of the traffic pattern and without ongoing collection of network information. We develop polynomial size LP models to design such a routing scheme. We discuss generalizations of the LP models to various radio transmission models. In an interference-limited scenario, we show how to guarantee schedulability of the oblivious routing. We present an extension to consider lossy links. We also discuss implementation issues. The LP models achieve performance close to what an oracle can achieve in the performance study. The results for multihop wireless networks with a single sink are especially good. We make a first stride in designing a traffic-oblivious energy-aware routing framework in multihop wireless networks.

An efficient scheme to remove crawler traffic from the Internet

We estimate that approximately 40% of current Internet traffic is due to Web crawlers retrieving pages for indexing. We address this problem by introducing an efficient indexing system based on active networks. Our approach employs strategically placed active routers that constantly monitor passing Internet traffic, analyze it, and then transmit the index data to a dedicated back-end repository. Our simulations have shown that active indexing is up to 30% more efficient than the current crawler-based techniques.

Multipath routing for mobile ad hoc networks

A Mobile Ad hoc NETwork(MANET) is a collection of wireless mobile computers forming a temporary network without any existing wire line infrastructure. Due to the dynamic nature of network topologies and the resource constraints, routing in MANETs is a challenging task. Multipath routing can increase end-to-end throughput and provide load balancing in wired networks. However, its advantage is not obvious in mobile ad hoc networks because the traffic flows along the multiple paths may interfere with each other. In addition, without accurate knowledge of topology, finding multiple node-disjoint paths is difficult. In this paper, we propose two on-demand methods to effectively search for multiple node-disjoint paths and present the path selection criteria. Compared with Dynamic Source Routing (DSR) and the Diversity Injection method, our methods can find more node-disjoint paths and thus provide source nodes with more choices to select good quality multiple paths. We also perform simulation studies on the proposed approaches. The simulation results show that our multipath routing methods can reduce the frequency of route discoveries and balance network loads. In addition, our Heuristic Redirection multipath routing method can reduce control overheads, improve end-to-end delay, and provide fair energy consumption among mobile hosts. The purpose of this paper is to present the advantages as well as the challenges of deploying multipath routing in mobile ad hoc networks.

A logical ring reliable multicast protocol for mobile nodes

A protocol for the reliable multicast of data to mobile hosts is described. A logical ring is maintained between all the base stations that handle the multicast traffic of the same multicast group. A token passing protocol enforces a consistent view between all base stations with respect to the frames that are considered delivered to all mobiles. The interaction of the reliable multicasting and the handoff events of the mobiles is controlled by a special handoff protocol. A description of the management protocol is also given. We use simulation results to illustrate the feasibility of the approach and reveal the performance interplay between the base station buffer size and the token rotation frequency.

Performance modeling of a channel reservation service

Certain applications, such as videoconferencing and information broadcast, require the ability to reserve network resources in advance. In a reservation system, users submit requests to a service center. Each request is characterized by a start time, a bandwidth requirement and a holding time. We consider a loss system where the service center rejects a request if it cannot accommodate the request at the preferred start time. Scheduling decisions may be made as soon as a request arrives or may be delayed until a later time. The latter allows the system to make more informed scheduling decisions, but the delay may be unacceptable to the users. In this paper, we investigate the benefits of delaying the scheduling decisions from the performance point of view. Our investigation is based on a reservation system that can accommodate a range of bandwidth requirements. Optimal scheduling decisions are first obtained for some static systems, that is, systems where all requests have arrived before the scheduling decisions are made. The results are then used to develop heuristic scheduling algorithms for systems with delayed decisions. Simulation results on the performance of these algorithms, as compared to a system where scheduling decisions are made immediately upon a requests arrival, are presented.

Impact of lossy links on performance of multihop wireless networks

Multihop wireless networks have unique features such as lossy links and interference. Both interference and lossy links affect the maximum achievable throughput of a network. Some wireless networks have energy constraints. Lossy links also affect energy efficiency due to retransmissions and broadcasting. We investigate the impact of lossy links on maximum achievable throughput and minimax energy utilization. These can be modeled as linear programming optimization problems. We give optimal solutions for both flow-based and destination-based routing. Experiments show that lossy links do have significant impact on the maximum achievable throughput. There are cases where a network can only achieve half of the throughput of the corresponding lossless network. The results show less significant impact of loss on energy efficiency. In some cases, the loss may be advantageous for energy efficiency, since the energy consumption may be reduced due to the loss of broadcasting messages. Experiments also show the significant impact of overhearing on energy efficiency.