Real Traffic Load Research Articles

Self-tuning fuzzy AQM mechanism based on traffic load and queue length

The existing fuzzy Active Queue Management(AQM) mechanisms mostly consider the queue length and its change rate as fuzzy inputs,while rarely consider the effect of packet arriving rate together.In order to design a more effective AQM algorithm,a novel fuzzy AQM algorithm called FQL-AQM was proposed.FQL-AQM considered both real queue length and average traffic load factor as fuzzy inputs,and regulated packet dropping probability through a fuzzy self-tuning algorithm.This algorithm can keep the queue length stable at the reference queue length level,and keep the average load factor stable at 1.And FQL-AQM can be well applied to a variety of network environments and can improve the network robustness. Simulation results show that FQL-AQM algorithm is efficient,stable and outperforms other proposed AQM algorithms in response rate,link utilization ratio,and queue length stability.

‘Low Noise Road Traffic’—The German research program, ‘LeiStra2’

LeiStra2' is a research program aimed at reducing road traffic noise at the source. It is a governmental funded program which comprises three parts: low noise tires, low noise roads and verification of results. In the course of the program it was possible to develop a new low noise truck tire, which has the potential to become the most quiet available truck tire. In another sub project a physical verified finite element method (FEM) software tool was developed, that is by now capable of simulating the structural vibration and noise emission from slick tires rolling on real road surfaces and thus can be used for the computer aided design of low noise tires. Current research in this sub program deals with the influence of the tread profile on the noise generation. In the research on a low noise road, a modified stone matrix asphalt pavement was realized that shows a noise reduction of 2 dB compared with conventional stone mastix asphalt. Furthermore, it is well know that porous asphalt layers have high sound absorption abilities, but unfortunately typically loose this ability after about eight years due to dirt clogging the pores. Within LeiStra2 we developed two measures that help to keep the sound absorbing abilities for a longer period. In particular the surface of the voids of the porous asphalt were covered with special polymeric material to prevent the voids from being clogged. In another sub project additional reactive sound absorbers were embedded in porous asphalt, which enhances the sound absorption and reduces the tire rolling noise by about 3 dB. Particularly annoying is the noise originating from vehicles rolling over expansion joints. Within LeiStra2 we succeeded in developing a new surface structure for conventional expansion joints, which substantially reduces the noise emission. These measures will be tested on various test tracks under real traffic load and environmental impact, which is the third subject of the program, the verification of the results. The program will be finished in summer or autumn 2009.

Limitation of Geosynthetics Usage on Road Subgrade

There are several ways of geosynthetics functionality. Well-known mechanisms are functions of separating, filtrating, protecting and slope reinforcing. There are several publications describing the influence of geosynthetics on increasing the soft-soil bearing capacity and their positive role on final subbase deformation. However, this geosynthetics functionality has not been explained satisfactorily in detail yet. The research presented here deals with clarifying the possible geosynthetics functionality. Six kinds of geosynthetics of world renowned producers were selected for testing. The measurement was carried out in the Geotechnical Laboratory Testing Field (GLTF), which is a facility constructed for fullscale geotechnical measurements. The results of static plate tests show that the contribution of the geosynthetics to the bearing capacity increase is very limited. A significant increase appears only in the case of a very low bearing capacity subgrade covered by a 20 cm thick subbase layer reinforced by some geosynthetics. After the static part of the experiment the GLTF was equipped with a cyclic loader to simulate real traffic loading and tests for the evaluation of possible bearing capacity increase and deformation decrease due to geosynthetics usage were repeated.

End-to-end performance aware association mechanism for wireless municipal mesh networks

In a wireless municipal mesh (muni mesh) network, a client station (STA) needs to associate with a mesh access point (MAP) for network access. Previous association mechanisms assume high-speed backhaul and only the access link being the bottleneck. This assumption holds for most WLANs, but in wireless mesh networks traffic could be bottlenecked either by the access link or by the bandwidth-limited wireless backhaul. In this paper, we propose a new joint MAP association mechanism for wireless muni mesh networks to improve STA’s end-to-end communication performance. A STA makes its association decision by jointly considering the quality of the access link between the STA and the associated MAP as well as the cost of the multi-hop path from the associated MAP to the Internet gateway. In addition, we design two new metrics, Contention Aware Expected Transmission Time (CAETT) and Load Aware Expected Transmission Time (LAETT), to measure the access link quality. The main strength of CAETT is incorporating the impact of 802.11 MAC layer contentions on the bandwidth sharing of multi-rate stations. LAETT further captures the real traffic load on the shared medium. In order to reduce the association delay, we use an analytical model to derive a hybrid measurement/estimation method to enable a station to quickly determine the cost of CAETT and LAETT. We conduct extensive simulations to evaluate the performance of the proposed joint MAP association mechanism. Especially within the joint association framework, we investigate the impact of various combinations of access link metrics (RSSI, PB, CAETT, LAETT) and backhaul routing metrics (hopcount, ETT, RALA) on the system performance. We show that the joint association mechanism can significantly improve the network performance in terms of throughput and delay by up to 100%. In particular, the joint association mechanism with LAETT as the access link metric and RALA as the routing metric outperforms other schemes and metrics.

High precision strain gauge measurements in areas of high stress concentrations of orthotropic plated bridge decks

The most critical part of the design of an orthotropic plated bridge deck is concerned with the fatigue resistance of the many welds in such a deck. Strain gauge measurements can constitute an important tool in acquiring better understanding of the complex stress field in the deck plate. However, to achieve this, the measurements need to be extremely precise since the gradient of the stress peaks shows rapid changes in the area under consideration and the influence zone for the stresses is extremely short. In addition, and since fatigue problems cannot be studied on scale models, the measurements need to be performed on full-scale models or on real prototype bridge decks subjected to real traffic load. Obviously, in these conditions, the use of strain gauges becomes far more difficult than it is in laboratory conditions. This article reports on two measurement series, carried out on recently built orthotropic plated bridge decks in Belgium. It details the practical implementation of the strain gauges and measurement apparatus and compares the strain results with finite element calculations to validate the precision of the measurements.

In VINI veritas

This paper describes VINI , a virtual network infrastructure that allows network researchers to evaluate their protocols and services in a realistic environment that also provides a high degree of control over network conditions. VINI allows researchers to deploy and evaluate their ideas with real routing software, traffic loads, and network events. To provide researchers flexibility in designing their experiments, VINI supports simultaneous experiments with arbitrary network topologies on a shared physical infrastructure. This paper tackles the following important design question: What set of concepts and techniques facilitate flexible, realistic, and controlled experimentation ( e.g. , multiple topologies and the ability to tweak routing algorithms) on a fixed physical infrastructure? We first present VINI's high-level design and the challenges of virtualizing a single network. We then present PL-VINI , an implementation of VINI on PlanetLab, running the "Internet In a Slice". Our evaluation of PL-VINI shows that it provides a realistic and controlled environment for evaluating new protocols and services.

Chasing errors through the network stack: a testbed for investigating errors in real traffic on optical networks

A testbed is described that allows both physical layer errors to be observed and analyzed, as well as monitoring network performance via frame loss. Real network traffic loads can be used for testing so that all measurements taken are representative of what would be seen in a deployed system. We illustrate our testbed with an examination of the behavior of a well-known networking standard, Gigabit Ethernet, in conditions of reduced receiver power on optical fiber. Our testbed results show that the line codes used to represent the data in the network affect the bit error rate for that data. Along with the previously reported result that bit error rate and packet error rate have only a weakly deterministic relationship, this highlights the need for testing of all network layers within a complete system carrying real-world traffic.

Performance of TCP over satellite networks under severe cross-traffic using GA

It has become increasingly important to test diverse Satellite Systems (Low Earth Orbit and Geosynchronous Satellites) under realistic traffic loads. None of the currently used techniques are able to achieve good results. Formal techniques can be applied to only over simplified models and statistical techniques relying on simulation often fail. Our approach relies on integrating the Genetic Algorithm (GA) with the simulator of the system under verification. We applied our approach to quantitative verification of the Satellite Transport Protocol (TCP Reno and TCP Vegas) successfully. Our simulation results are better than those achieved by traditional statistical methods.

성능향상된 교량 바닥판의 확률론적 해석 및 수명연장 분석

Although the strengthening effect of deteriorated concrete bridge decks has been studied by various authors, most researches are focused on the experimental works on the pulsating loading in laboratory in spite of deterioration of deck caused by moving vehicle loads. In this research, a theoretical live load model that was proposed to reflect an effect of moving vehicle loads is formulated from a statistical approach on the measurement of real traffic loads for various time periodsin Korea. Fatigue life and strengthening effect of strengthened bridge decks strengthened with either Carbon Fiber Sheet or Grid typed Carbon Fiber Polymer Plastic by the probabilistic and the reliability analyses are assessed. As a results, secondary bridge deck (DB18) strengthened with FRP ensures a sufficient fatigue resistance against the increased traffic loads as well as load carrying capacity in life cycle.

Analysis of Reflective Crack Control System Involving Reinforcing Grid over Base-Isolating Interlayer Mixture

To develop a rigorous, mechanistic design method for asphalt overlays, one must have a method to accurately determine the response of the overlay system to various load conditions. This paper presents a cutting-edge nonlinear three-dimensional finite-element modeling approach for asphalt overlay analysis, including a viscoelastic constitutive model and realistic traffic and environmental load conditions. These tools were used to analyze a proposed reflective crack control system for Taxiway E at the Greater Peoria Regional Airport (GPRA), involving a base-isolating interlayer mixture used in conjunction with a glass-fiber reinforcement layer. The use of a base-isolating interlayer below the asphalt overlay was found to greatly reduce tensile and shear stresses in the asphalt overlay. Based upon expected critical cooling events and design aircraft at GPRA, critical overlay and interlayer stresses were found to be predominantly load associated. The base-isolating interlayer was predicted to develop localized stresses in the vicinity of the existing crack well beyond the yield threshold, based upon linear viscoelastic analysis. This suggests the importance of designing a tough, ductile interlayer mixture that can tolerate localized yielding under repeated load applications.

Determination of effective stress range and its application on fatigue stress assessment of existing bridges

Abstract This paper presents a unified approach on determination of the effective stress range based on equivalent law of strain energy and fatigue damage model, so as to provide an efficient approach for accurately assessing effective fatigue stress of existing bridge under traffic loading. A new theoretical framework to relate variable- and constant-amplitude fatigue is proposed in this paper. Different formulation for calculating effective stress range can be derived by the proposed theory, which include the effective stress range by the root mean square, by Miner's law and a new effective stress range based on the nonlinear fatigue damage model. Comparison of the theoretical results of fatigue damage under the effective stress range of the variable-amplitude stress spectrum and experimental data of fatigue damage under realistic traffic loading has confirmed the validity of the proposed theory. As a way to relate variable-amplitude fatigue data with constant-amplitude data, the effective stress range provides the most convenient way for evaluating fatigue damage under variable-amplitude loading. The proposed theory is then applied to provide an efficient approach for accurately assessing fatigue damage of existing bridges under traffic loading, in which online strain history data measured from bridge structural health monitoring system is available. The proposed approach is applied to evaluate the effective stress range for the purpose of the fatigue analysis of a deck section of a long-span steel bridge––the Tsing Ma Bridge in Hong Kong.

Online error detection through observation of traffic self-similarity

The authors present a new and universally applicable approach to error detection in packet or cell communication networks. The error detection uses measured traffic load data. The advantage is that detection of an error in a low layer reduces the probability of an undetected error in higher layers, and makes time-costly error detection in higher layers unnecessary. Most systems use static traffic load thresholds for error detection. The authors present an approach which can achieve considerably higher sensitivity. Their basic idea is to exploit the property of self-similarity in network traffic. This analytical redundancy gives a reference behaviour of the network traffic load, which allows the detection of faulty behaviour in the real network traffic load. For the error detection, the validity of the given self-similar property is checked through a deviation indicator Q based on second-order properties of the time series' distributions. This is a sufficient condition for normal (error-free) behaviour.

Effects of ‘road friendly’ suspensions on long-term flexible pavement performance

This paper examines the effects of ‘road friendly’ heavy goods vehicle suspensions on long-term flexible pavement performance. A deterministic ‘whole-life pavement performance model’ (WLPPM) is used to calculate pavement damage due to realistic traffic and environmental loading. The traffic is modelled first as a fleet of steel-sprung heavy goods vehicles and second as a fleet of ‘road friendly’ air-suspended vehicles. The pavement life predictions are compared for the two cases and with results from a simple road damage analysis based on the ‘fourth power law’. It is concluded that changing to a fleet of ‘road friendly’ vehicles would not significantly affect the life or maintenance costs of thicker asphalt pavements (motorways and trunk roads) where the mode of failure is permanent deformation (rutting). However, the life of thinner pavements (minor roads) that fail by fatigue damage and pot-holing would be increased significantly if the vehicle fleet changed to road friendly suspensions. Predictions from the simplified fourth power law approach tend to significantly overestimate the benefits of road friendly suspensions for major road conditions compared to the WLPPM predictions. It is concluded that the potential economic benefits in England and Wales of converting to air suspensions may be only 30 per cent of those predicted by the authors of the EC ‘road friendly suspensions’ regulations.

Effects of Spatial Repeatability On Long-Term Flexible Pavement Performance

The effects of spatial repeatability of dynamic tyre forces on the long-term performance of three typical British pavement constructions are investigated. Long-term pavement performance is calculated using a ‘whole-life pavement performance Model’ (WLPPM). The WLPPM is capable of predicting deterministic pavement damage due to realistic traffic and environmental loading, throughout the life of the pavement. Particular attention is given to modelling dynamic tyre forces and patterns of loading applied to the pavement by a typical fleet of heavy vehicles. A method is described for simulating vehicle fleets with varying degrees of spatial repeatability using a small number of dynamic tyre force histories. Results indicate that thinner pavements are most sensitive to the level of spatial repeatability exhibited by the vehicle fleet. Pavement damage predictions made without assuming an appropriate level of spatial repeatability can be in error by 20–150 per cent, the higher values being for thinner pavements that fail by fatigue damage.

A Model of Whole-Life Flexible Pavement Performance

A new ‘whole-life’ pavement performance model (WLPPM), which is capable of making deterministic pavement damage predictions due to realistic traffic and environmental loading, has been developed. A vehicle simulation is used to generate dynamic tyre forces that are a function of distance along the road. These dynamic tyre forces are then combined with the appropriate pavement primary response influence functions (stress, strain and displacement) to give primary response histories at regularly spaced points along the pavement. The primary response histories are then transformed into pavement damage (fatigue and permanent deformation) using an appropriate damage model. The result is an increment of damage at each point along the pavement due to a single vehicle pass. The pavement surface profile is then updated to reflect permanent deformation damage and the layer material parameters are changed to reflect fatigue damage. The procedure is then repeated for the next vehicle pass. Particular attention is given to modelling strength variations in the pavement and dynamic tyre forces. The model is used to investigate the relationship between ‘hot spots’ (due to peak dynamic loads), ‘weak spots’ (due to initial pavement stiffness variations) and long-term pavement damage.

Parametric Study of Factors Affecting Flexible-Pavement Performance

A new whole–life pavement–performance model (WLPPM) that is capable of making deterministic pavement–damage predictions due to realistic traffic and environmental loading has been developed. A vehicle simulation is used to generate dynamic tire forces that are a function of distance along the pavement. These dynamic tire forces are then combined with the appropriate pavement primary–response influence functions to give primary–response histories at regularly spaced points along the pavement. The primary–response histories are then transformed into an increment of damage at each point along the pavement due to a single vehicle pass, and the surface–roughness profile is updated. This procedure is then repeated until pavement failure occurs. Using the WLPPM, the performance of two classes of pavement are examined operating under climatic conditions typical of the United Kingdom. It is concluded that both dynamic vehicle loads and asphalt–layer stiffness variations can significantly influence long–term flexible–pavement performance.

Taming Xunet III

An architecture for network management and control for emerging wide-area ATM networks is presented. The architecture was implemented on XUNET III, a nationwide ATM network deployed by AT&T. The Xunet network management system is based on the OSI standards and includes configuration, fault and performance management. An OSI agent resides at every switching node. Its capabilities include monitoring of cell level quality of service in real time and estimation of the schedulable region. The complexity and accuracy of real-time monitoring functionalities is investigated. To provide realistic traffic loads, distributed traffic generation systems both at the cell and call level have been implemented. In order to study the trade-off between the network transport and signalling system we have implemented a virtual path signalling capability. Our experiments show that the ability of a network to admit calls is limited by two distinct factors: the capacity of the network and the processing power of the signalling system. Depending on the bandwidth requirement of calls, the limit of one or the other will be first reached. This is a key observation, unique to broadband networks.