Path Quality Research Articles

Loose Guide for Passive Omnidirectional Mobility Aid

This paper details the design and control of an intelligent mobility aid for the elderly and gait-disabled, called Omni RT Walker (ORTW). Omni RT Walker-II, version 2 of ORTW, consists of an omnidirectional platform and uses magneto-rheological brakes for passive control. ORTW-II enables the elderly to use the driving skills they possess while supplementing movement that may have declined due to their age or fatigue. We choose indoor navigation as the task to be realized by shared control of ORTW-II. Unlike most path tracking methods, which attempt to lead an objective system on a desired trajectory, our new algorithm restricts mobility to a pathway called thePotential Canal, while mobility is conducted by the user. In systems with direct human interaction similar to mobility aids, our proposal is expected to increase user-dependability in system operation while increasing user freedom and safety. A collision-free Potential Canal is maintained using realtime modification based on environmental information. Experimental results are included to demonstrate path tracking accuracy and quality.

The state of work on automated monitoring and control of water chemistry at power stations and prospects for their future development

Materials on an automated system for chemical monitoring and control (ASCMC) of the water chemistry in the steam-water path of a thermal power station are presented. The equipment of the main subsystems within the ASCMC is considered, including its process subsystem, which comprises automatic analyzers of the quality of the steam-water path, and the information-computational subsystem. The latter is implemented using a hardware and software system that acquires, processes, and transmits information to the work-stations of the operators in charge of the water chemistry of the thermal power station.

Real-time traffic support in heterogeneous mobile networks

Multi-hop mobile wireless networks have been proposed for a variety of applications where support for real-time multimedia services will be necessary. Support for these applications requires that the network is able to offer quality of service (QoS) appropriate for the latency and jitter bounds of the real-time application constraints. In this paper, we analyze the primary challenges of realizing QoS in mobile wireless networks with heterogeneous devices and propose a QoS framework for real-time traffic support. We address the problem in three ways: estimate the path quality for real-time flows, mitigate the impact of node heterogeneity on service performance, and reduce the impact of interfering non-real-time traffic. Specifically, our proposed QoS framework first utilizes a call setup protocol at the IP layer to discover paths for real-time flows, as well as to perform admission control by accurate service quality prediction. The underlying routing protocol also enables transparent path selection among heterogeneous nodes to provide stable paths for real-time traffic delivery. We then use a prioritized MAC protocol to provide priority access for flows with real-time constraints to reduce interference from unregulated non-real-time traffic. We foresee the utility of our proposed solution in heterogeneous mobile networks, such as campus or community-wide wireless networks. In these environments, resource-rich or fixed wireless routers may be leveraged to achieve better service quality when heterogeneity of node capability and movement is significant. Through experimental results, we demonstrate the utility and efficiency of our approach.

Statistically assisted routing algorithms (SARA) for hop count based forwarding in wireless sensor networks

The main goal of this paper is to provide routing–table-free online algorithms for wireless sensor networks (WSNs) to select cost (e.g., node residual energies) and delay efficient paths. As basic information to drive the routing process, both node costs and hop count distances are considered. Particular emphasis is given to greedy routing schemes, due to their suitability for resource constrained and highly dynamic networks. For what concerns greedy forwarding, we present the Statistically Assisted Routing Algorithm (SARA), where forwarding decisions are driven by statistical information on the costs of the nodes within coverage and in the second order neighborhood. By analysis, we prove that an optimal online policy exists, we derive its form and we exploit it as the core of SARA. Besides greedy techniques, sub–optimal algorithms where node costs can be partially propagated through the network are also presented. These techniques are based on real time learning LRTA algorithms which, through an initial exploratory phase, converge to quasi globally optimal paths. All the proposed schemes are then compared by simulation against globally optimal solutions, discussing the involved trade–offs and possible performance gains. The results show that the exploitation of second order cost information in SARA substantially increases the goodness of the selected paths with respect to fully localized greedy routing. Finally, the path quality can be further increased by LRTA schemes, whose convergence can be considerably enhanced by properly setting real time search parameters. However, these solutions fail in highly dynamic scenarios as they are unable to adapt the search process to time varying costs.

Environment and parental factors as determinants of mode for children's leisure travel

This study was aimed at increasing our understanding of environmental and parental factors influencing mode choice for children's journeys to organized leisure activities. Three hundred and fifty-seven Swedish parents of 8–11-year-old children completed a questionnaire and kept a travel diary. The design of urban environment, in which the families lived, was assessed by a group of five experts. By means of multiple regression analyses it was found that the parents’ attitude towards chauffeuring was related to environmental factors such as traffic environment, quality of footpaths and cycle paths, and sense of community as well as the number of cars in the household. The attitude towards independent travel was related to characteristics of the child, such as age and maturity, and individual parental factors, such as trust and the need to protect their child, and whether there were older children in the household. Both the relative frequency of journeys made independently and by car was related to the parent's attitude towards independent travel, as well as environmental and parental factors. To decrease car usage and increase children's independent travel to leisure activities, planners and policy-makers should focus on improvements in the traffic environment and promote a favourable attitude towards independent travel.

Packet path assurance for IP networks

This paper proposes a fast and simple technique, called packet path assurance (PPA) test, for admission control in packet networks that provide multimedia applications such as Voice over IP (VoIP). The distinctive features of the PPA test are that it uses active probes to evaluate the quality of the media path and that it runs in near real-time during the connection set-up interval; for example, during Session Initiation Protocol (SIP) connection set-up phase. Due to the limited amount of time available during a connection setup, only a small number of probe packets can be transmitted. We evaluate the efficacy of the PPA test for connection admission control (CAC). We design an admission control rule based on a statistical analysis of the data obtained from the PPA test. Our experiment confirms that a relatively small number of probe packets are adequate to support an efficient CAC test. The Packet Path Assurance technique is covered by Lucent patent applications.

Designing the Walkable City

With federal policy beginning to shift from auto-centric planning, provision for pedestrian and bicycle access is now mandated in federally supported projects. However, the field of transportation planning has little in the way of theory and methods to guide design and planning for walkable cities. Walkability is increasingly valued for a variety of reasons. Not only does pedestrian transportation reduce congestion and have low environmental impact, it has social and recreational value. Recent research suggests that walking also promotes mental and physical health. The quality of the pedestrian environment is key to encouraging people to choose walking over driving. Six criteria are presented for design of a successful pedestrian network: (1) connectivity; (2) linkage with other modes; (3) fine grained land use patterns; (4) safety; (5) quality of path; and (6) path context. To achieve walkable cities in the United States it will be necessary to assess current walkability conditions, revise standards and regulations, research walking behavior in varied settings, promote public education and participation in pedestrian planning, and encourage collaboration and interdisciplinary education between transportation engineers and the design professions.

Geometric spanners for routing in mobile networks

We propose a new routing graph, the restricted Delaunay graph (RDG), for mobile ad hoc networks. Combined with a node clustering algorithm, the RDG can be used as an underlying graph for geographic routing protocols. This graph has the following attractive properties: 1) it is planar; 2) between any two graph nodes there exists a path whose length, whether measured in terms of topological or Euclidean distance, is only a constant times the minimum length possible; and 3) the graph can be maintained efficiently in a distributed manner when the nodes move around. Furthermore, each node only needs constant time to make routing decisions. We show by simulation that the RDG outperforms previously proposed routing graphs in the context of the Greedy perimeter stateless routing (GPSR) protocol. Finally, we investigate theoretical bounds on the quality of paths discovered using GPSR.

A P2P Network Model with Multi-Layer Architecture Based on Region

Gnutella application layer protocol simply uses flooding algorithm to route peer’s querying, which is just implemented on application layer and doesn’t use down-layer’s information routing of Internet. So it has poor scalability and low efficiency. This paper uses the model of “small world and power law” as the theoretical foundation, and in the light of the users’ requirement and a shared organization layer and region of logic manage-unit, a new distributed peer-to-peer network model of RLP2P(region-layer P2P) with multi-layer structure based on region is proposed, and its prototype system is implemented. A new optimized Multilayer Light-Gossip route strategy is implemented. This paper studies the stress and stretch with the model which has two intuitive metrics of goodness defined to evaluate the quality of the data paths. At the same time, the idea is put forward about the tradeoffs between the stress and stretch. Simulation results about RLP2P’s protocol show that it could effectively solve the above problems, and the larger the network size is, the more obvious the superiority of its comprehensive performance is. So the model is reasonable and effective.

Geometric spanners for routing in mobile networks

We propose a new routing graph, the restricted Delaunay graph (RDG), for mobile ad hoc networks. Combined with a node clustering algorithm, the RDG can be used as an underlying graph for geographic routing protocols. This graph has the following attractive properties: 1) it is planar; 2) between any two graph nodes there exists a path whose length, whether measured in terms of topological or Euclidean distance, is only a constant times the minimum length possible; and 3) the graph can be maintained efficiently in a distributed manner when the nodes move around. Furthermore, each node only needs constant time to make routing decisions. We show by simulation that the RDG outperforms previously proposed routing graphs in the context of the Greedy perimeter stateless routing (GPSR) protocol. Finally, we investigate theoretical bounds on the quality of paths discovered using GPSR.

Performance of a new bus assignment algorithm for an ATM switch fabric

The measurement of the quality of service in ATM* networks involves the activation of the ATM layer management OAM functions. Once an ATM connection is set up, in-service performance monitoring based on OAM cells can be used to measure and estimate the ATM layer QoS parameters. In-service measurement of ATM layer QoS parameters such as cell delay variation, cell transfer delay, cell loss ratio, etc., is necessary to verify on one hand, if the network is meeting the requested QoS and on the other hand, if the users are receiving their promised QoS. Congestion conditions in ATM switches may cause gradual deteriorations in the quality of virtual paths or virtual channel connections in an ATM network. QoS measurement using OAM cells can accurately measure the overall quality of monitored ATM layer QoS parameters in order to detect such deteriorations before the service quality has dropped bellow an acceptable level. Several factors such as network load, congestion, bottlenecks, and incremenTS in network load may affect the cell delay variation of video transmissions in an ATM network. In this work, several ATM layer QoS parameters have been measured on a VBR video source using OAM cells. The simulation resulTS obtained show that with low network loads, the contribution of each individual ATM switch to the local and to the end-to-end CDV is not significant. In the presence of a bottleneck switch, the CDV presented by this switch becomes the dominant one at both local and end-to-end sides. When the network load is between 0.5 and 0.6, small incremenTS in network load do not alter the buffer performance of the non-congested ATM switches, and low values of CDV can be obtained. In contrast, it was found that there is a critical load between 0.65 and 0.7 where small incremenTS in network load may force the CDV to grow abruptly.

A survey of application level multicast techniques

Application level multicasting is increasingly being used to overcome the problem of non-ubiquitous deployment of IP multicast across heterogeneous networks. To the best of our knowledge, this paper is among the first papers [A comparative study of application layer multicast protocols, Unpublished report; IEEE Network, January/February, 2003] to provide a comprehensive survey of most of the various milestone research work in application level multicast in terms of both breadth and depth. The paper classifies them into different broad categories based on their topology design, service model and architecture to facilitate better understanding of their contributions and discuss their merits and limitations. As these techniques vary widely in their goals, designs, performance evaluation metrics and evaluation strategies, it is impossible to quantify their relative performance. However, this paper is able to provide a comparative insight into their performance through the use of a set of evaluation metrics identified to be common to the techniques and are directly related to their performance and whose data can be derived and inferred from their designs. The metrics used here include scaleability measured intuitively in terms of the size of the multicast receivers it can support, the protocol efficiency in terms of the quality of data paths, control overheads, amount of state information to be maintained at each member node and failure tolerance.

Protection performance components in MPLS networks

In this paper, we present a new methodology for evaluating fault recovery performance of some existing mechanisms, which considers the establishment of quality of service network paths with protection. In order to evaluate the level of protection of a network, different components, such as protection parameters (packet loss and restoration time), or network parameters and constraints (link failure probability and network load), are analyzed. A formulation to calculate the influence of each component in the establishment of protected paths is discussed in multiprotocol label switching (MPLS) networks. Several experiments are presented to support this formulation. Moreover, an analysis of the relationship between these protection components and different traffic classes is also introduced and justified.

Path Selection Methods With Multiple Constraints in Service-Guaranteed WDM Networks

We propose a new approach to constraint-based path selection for dynamic routing and wavelength allocation in optical networks based on WDM. Our approach considers service-specific path quality attributes, such as physical layer impairments, reliability, policy, and traffic conditions, and uses a flooding-based transfer of path information messages from source to destination to find multiple feasible paths. It is fully decentralized, as it uses local network state information. To better understand how multiple constraints impact the efficiency of wavelength routing, and consequently provision the service guarantees, we specifically focus on electronic regenerators that, while being widely considered as the basic building blocks for optical switching nodes, are likely to impose conflicting constraints on routing. For example, electronic regenerators extend the optical reach and could perform wavelength shifting, but also induce impairments, such as delays and operational costs. The question for constraint-based routing is how to account for these conflicting effects. To validate the network modeling, a wide range of networking scenarios are simulated, such as ring, mesh and interconnections of all-optical networks with electronic gateways. For all these scenarios, our approach is shown to efficiently accommodate multiple, conflicting routing metrics related to different services and network architectures.

Kinetic energy control in action-derived molecular dynamics simulations

We present a computational approach to obtain classical atomic trajectories for given initial and final atomic configurations. By introducing an additional penalty function to the action of Passerone and Parrinello [Phys,Rev. Lett. 87, 108302 (2001)] the quality of atomic trajectories is greatly improved in terms of the Onsager-Machlup action. We demonstrate that this variant of the action is useful for improving path quality and consequently for atomic trajectory annealing. We utilize the one-way multigrid method as an efficient relaxation method for the construction of trajectories. The implementation of the proposed approach to a general system is quite straightforward as in the case of ordinary molecular dynamics simulations, i.e., the only requirement is to evaluate the potential energy and the atomic forces.

An efficient QoS routing algorithm for quorumcast communication

This paper studies quality of service (QoS) routing for quorumcast, a generalized form of multicast communication. The need of quorumcast communication arises in a number of distributed applications such as distributed synchronization and resource discovery, but little work has been done on routing quorumcast messages with or without QoS constraints. Moreover, most known research work aimed to construct a minimum cost tree that spans the source and the quorumcast group members. In this paper, we further consider the path quality of a tree in terms of source–destination delay constraints imposed by applications that use the tree. As the delay-constrained quorumcast routing problem is NP-complete, we propose an efficient heuristic QoS routing algorithm. We also consider how to detect and remove loops in the course of tree construction and how to deal with member join/leave in/from the quorumcast pool. Our simulation study shows that the proposed algorithm performs well and constructs a quorumcast tree with the cost close to that of the “optimal” routing tree.

Path quality measures for sensor-based motion planning

A mobile robot requires the perception of its local environment for position estimation. Traditional planning methodologies build plans by considering the obstacles position in the environment, and assume that the sensorial system is able to localize the robot. Not all sensorial systems are able to maintain the robot accurately localized at each instant and require a perception planning process to localize the robot at certain points. Recent works of different researchers, tend to overcome the problem of simultaneous perception-action planning. To plan simultaneously perceptual localization activities and movements it is required to determine the robot’s position uncertainty evolution and how does this uncertainty affect the perceptual problem in order to localize the mobile robot. The proposed algorithm provides a methodology to evaluate the uncertainty in an indoor semi-structured environment, which can be used to plan the robot’s movements and localization perception actions, and achieve an integrated plan able to reach the goal. The planning includes the position uncertainty analysis and the probability of success calculation as a path quality measurement. The resultant module has been integrated successfully in a more complex navigation system. Experiments demonstrate the effectiveness of the proposed method in real world applications.

Performance of multihop wireless networks

Existing wireless ad hoc routing protocols typically find routes with the minimum hop-count. This paper presents experimental evidence from two wireless test-beds which shows that there are usually multiple minimum hop-count paths, many of which have poor throughput. As a result, minimum-hop-count routing often chooses routes that have significantly less capacity than the best paths that exist in the network. Much of the reason for this is that many of the radio links between nodes have loss rates low enough that the routing protocol is willing to use them, but high enough that much of the capacity is consumed by retransmissions. These observations suggest that more attention be paid to link quality when choosing ad hoc routes; the paper presents measured link characteristics likely to be useful in devising a better path quality metric.

Service Locating for Large-Scale Mobile Ad-Hoc Network

In a mobile ad-hoc network, an efficient service discovery system is needed to locate various service providers. However, because an ad-hoc network has no fixed topology, its service locating is quite different from traditional schemes for the Internet. In this article, we present a novel service locating system specifically designed for large-scale mobile ad-hoc networks. In our system, a subset of nodes is dynamically elected and self-organized into a virtual backbone (VB). These VB nodes manage the directory information of services and monitor path quality of service on behalf of end users. Such information is then used to direct the selection of appropriate providers. We evaluate the performance of our system through simulation. The result demonstrates that the proposed locating system greatly improves the quality of service delivery while maintaining reasonably low cost.

Improvement of conductive network quality in carbon black‐filled polymer blends

AbstractHeat treatment of polymer‐based composites is critical for the enhancement of both stability and long‐term service life, especially when the materials function under an inconstant temperature environment. The present article discusses the effect of heat‐treatment conditions on the electrically conductive properties of carbon black (CB)‐filled low‐density polyethylene (LDPE) and ethylene–vinyl acetate copolymer (EVA) composites, which are candidates for positive temperature coefficient (PTC) materials. It was found that the dispersion mode of CB particles changes as a function of the matrix morphology. When the composites are irradiated to form crosslinked networks in the matrix for the elimination of negative temperature coefficient (NTC) behavior, some of the produced free radicals are also entrapped for quite a long time after the irradiation treatment. These residual radicals further enhance the interaction between CB and the matrix and further induce the crosslinking of the matrix so that the composites' conductivity changes with time as a result of the continuous variation in the contacts between the conductive fillers. To improve the quality of the conduction paths in the composites, appropriate post‐heat treatment should be carried out, which speeds up the formation of the above‐mentioned two kinds of crosslinked structures within a limited time. Annealing at 75°C for more than 10 h is believed to be an effective way. After the treatment, a balanced performance characterized by reduced room‐temperature resistivity and improved PTC intensity was obtained. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2768–2775, 2002