Showing papers on "Network traffic simulation published in 2001"

Optimizing traffic lights in a cellular automaton model for city traffic.

Abstract: We study the impact of global traffic light control strategies in a recently proposed cellular automaton model for vehicular traffic in city networks. The model combines basic ideas of the Biham-Middleton-Levine model for city traffic and the Nagel-Schreckenberg model for highway traffic. The city network has a simple square lattice geometry. All streets and intersections are treated equally, i.e., there are no dominant streets. Starting from a simple synchronized strategy, we show that the capacity of the network strongly depends on the cycle times of the traffic lights. Moreover, we point out that the optimal time periods are determined by the geometric characteristics of the network, i.e., the distance between the intersections. In the case of synchronized traffic lights, the derivation of the optimal cycle times in the network can be reduced to a simpler problem, the flow optimization of a single street with one traffic light operating as a bottleneck. In order to obtain an enhanced throughput in the model, improved global strategies are tested, e.g., green wave and random switching strategies, which lead to surprising results.

Dynamic network traffic assignment and simulation methodology for advanced system management applications

Abstract: Evaluation and operation of intelligent transportation system technologies in transportation networks give rise to methodological capabilities that require description of the dynamics of network traffic flows over time and space. Both descriptive and normative dynamic traffic assignment capabilities are required in this environment. Several dynamic network flow modeling problem formulations that arise in this context are discussed, and simulation-assignment procedures are described for these problems. A dynamic traffic assignment (DTA) system for advanced traffic network management is described. It is built around a traffic simulation-assignment modeling framework, which describes the evolution of traffic patterns in the network for given traffic loading under particular control measures and route guidance information supply strategies to individual motorists. The simulator is also embedded in an interactive search algorithm to determine optimal route guidance instructions to motorists. Numerical experiments with the model illustrate the relative effectiveness of different information supply strategies under different user behavior response rules.

Method and system for profiling network flows at a measurement point within a computer network

Abstract: A method and system for profiling network flows at a measurement point within a computer network is provided. The method includes measuring network flows having invariant features at a measurement point located within routing infrastructure of the computer network to obtain flow statistics. The method also includes aggregating the flow statistics to obtain a traffic profile of the network flows at the measurement point. The method and system utilize the natural hierarchy in the Internet addressing scheme to provide a means for making tractable measurements of network traffic in high-speed networks. Moreover, the method and system adapt dynamically to the changing underlying traffic characteristics to maintain a maximum memory footprint for the profiles. The method and system adapt by adjusting the level of aggregation of the traffic endpoints along a scale from Interface to fully specified network address.

Traffic theory and the Internet

Abstract: We argue that traffic theory, an essential component in the design of traditional telecommunications networks, should be increasingly applied in the development of the multiservice Internet. We discuss the statistical characteristics of Internet traffic at different time scales. Modeling is facilitated on identifying the notion of flow and distinguishing the categories of streaming and elastic traffic. We review mathematical modeling approaches useful for predicting the relationship between demand, capacity and performance for both streaming and elastic flows. Derived results indicate the limitations of service differentiation as a means for guaranteeing QoS and highlight the importance of traditional traffic engineering approaches in ensuring that the network has sufficient capacity to handle offered demand.

A study of networks simulation efficiency: fluid simulation vs. packet-level simulation

Abstract: Network performance evaluation through traditional packet-level simulation is becoming increasingly difficult as today's networks grow in scale along many dimensions. As a consequence, fluid simulation has been proposed to cope with the size and complexity of such systems. This study focuses on analyzing and comparing the relative efficiencies of fluid simulation and packet-level simulation for several network scenarios. We use the "simulation event" rate to measure the computational effort of the simulators and show that this measure is both adequate and accurate. For some scenarios, we derive analytical results for the simulation event rate and identify the major factors that contribute to the simulation event rate. Among these factors, the "ripple effect" is very important since it can significantly increase the fluid simulation event rate. For a tandem queueing system, we identify the boundary condition to establish regions where one simulation paradigm is more efficient than the other. Flow aggregation is considered as a technique to reduce the impact of the "ripple effect" in fluid simulation. We also show that WFQ scheduling discipline can limit the "ripple effect", making fluid simulation particularly well suited for WFQ models. Our results show that tradeoffs between parameters of a network model determines the most efficient simulation approach.

Expanding confidence in network simulations

Abstract: Networking engineers increasingly depend on simulation to design and deploy complex, heterogeneous networks. Similarly, networking researchers increasingly depend on simulation to investigate the behavior and performance of new protocol designs. Despite such widespread use of simulation, today there exists little common understanding of the degree of validation required for various applications of simulation. Further, only limited knowledge exists regarding the effectiveness of known validation techniques. To investigate these issues, in May 1999 DARPA and NIST organized a workshop on Network Simulation Validation. This article reports on discussions and consensus about issues that arose at the workshop. We describe best current practices for validating simulations and for validating TCP models across various simulation environments. We also discuss interactions between scale and model validation and future challenges for the community.

A method and system to implement policy-based network traffic management

Abstract: A method to implement policy-based network traffic management includes receiving data (16) pertaining to a network device at a network traffic manager (10), the first data (A) being received out-of-band of network traffic. Second data (B) is extracted from the network traffic. A network traffic management policy (18) is implemented at the network traffic manager utilizing the first and second data.

A cellular automaton traffic flow model for online simulation of traffic

Abstract: We present a simulation tool to predict urban traffic based on a cellular automaton model for traffic flow supplemented by real-traffic data. This tool is applied to the road network of the inner city of Duisburg. The quality of the reproduced traffic states is investigated with regard to vehicle densities and key features of urban traffic like rush-hours which are resembled quite well.

Traffic engineering system and method

Abstract: The present invention is directed to a novel system and method for traffic engineering in a packet-switched network, such as an Internet Protocol (“IP”) based backbone network A global view of the network is constructed utilizing a network data model that can be readily constructed from the balkanized network information associated locally with the individual elements in the network The data model, in turn, can be utilized to support useful traffic engineering tools such as routing modeling and visualization

SWiMNet: a scalable parallel simulation testbed for wireless and mobile networks

Abstract: We present a framework, called SWiMNet, for parallel simulation of wireless and mobile PCS networks, which allows realistic and detailed modeling of mobility, call traffic, and PCS network deployment. SWiMNet is based upon event precomputation and a combination of optimistic and conservative synchronization mechanisms. Event precomputation is the result of model independence within the global PCS network. Low percentage of blocked calls typical for PCS networks is exploited in the channel allocation simulation of precomputed events by means of an optimistic approach.Various experiments were conducted to study the performance and scalability of SWiMNet using a realistic mobility model and executed on a cluster of workstations. Experimental results indicate that our parallel simulation model yields good speedup, and significantly reduces the execution time compared to a sequential implementation. Finally, an analytical study of our PCS simulation model is also presented and compared with the experimental results. Our model is found to be consistent with the analytical study.

A hybrid optimization-mesoscopic simulation dynamic traffic assignment model

Abstract: The evaluation of ITS measures, such as advanced traveler information systems and advanced traffic management systems depend heavily on the use of faster than real time traffic simulation methods. Although many micro-simulation traffic models have already been developed, their execution times are still too slow for large-scale ITS applications. This has lead to the development of mesoscopic simulation and traffic assignment methods. These are simpler traffic models, which trade off some of the fidelity of the results for significant gains in computation time. This paper presents a new dynamic traffic assignment model that is based on the mesoscopic space-time queue network loading method developed by Mahut (2000). This hybrid optimization simulation method was applied to a portion of the Stockholm road network, which consists of 220 zones, 2080 links and 5000 turns.

Method and system for controlling network traffic to a network computer

Abstract: A method and system for controlling network traffic to a network computer such as a server is provided wherein such control is provided based on a measured capacity of the sever to service the network traffic and rule data which represents different policies for servicing the network traffic. A load-controller of the system installs more or less restrictive packet or request filtering policies based on the capacity of the server to throttle the traffic to the server. The method and system are sensitive to the actual capacity of the server by adopting this adaptive traffic-shaping feature instead of using rigid policies to control resource usage on the server.

Traffic control in an ip based network

Abstract: According to the present invention, traffic control in an IP based network is provided. For this purpose, traffic situation in the network is measured, and the traffic flow is controlled on the basis of the measured traffic situation. Moreover, an operator may define rules for different measured situations, and the traffic flow is controlled on the basis of these rules.

Estimation of dynamic origin-destination flows from sensor data using bi-level optimization method

Abstract: Numerous methods have been proposed to estimate origin-destination (OD) flows from traffic counts. In most of the formulations, link-flow proportions play a key role, though often their dependence on the unknown demand flows is ignored. A few studies have addressed this problem in the static case. In this paper, a bi-level optimization method is used to address this problem to estimate time-dependent OD flows from on-line or archived traffic data. In the upper level the generalized least-squares estimation method is used and in the lower level the network equilibrium is satisfied. The proposed method is implemented as an internal module of a well-established dynamic traffic assignment simulation program (DYNASMART-P); hence it can also be used to improve the external consistency of the simulation. The performance of the procedure is investigated through a set of experiments performed on a test network under varying network congestion levels

Intelligent simulation and prediction of traffic flow dispersion

Abstract: Dispersion of traffic flow on urban road segments is often described by some typical statistical models such as the normal distribution model and the geometric distribution model. These probability-based models can fit traffic flow well under ideal physical environments but may not work satisfactory in certain complex cases because of their strict mathematical assumptions. A neural network-based system identification approach is used to establish an auto-adaptive model for simulating traffic flow dispersion. This model, being feasible to a wide variety of traffic circumstances, can be calibrated and used for on-line traffic flow forecasting. Data simulation and field-testing show reliable performance of the proposed intelligent approach.

On the impact of aggregation on the performance of traffic aware routing

Abstract: This paper investigates the impact of traffic aggregation on the performance of routing algorithms that incorporate traffic information. We focus on two issues. Firstly, we explore the relationship between average network performance and the coarseness (granularity) of traffic splitting across routes. Specifically, we are interested in how average network performance improves with our ability to distribute traffic arbitrarily across multiple paths. Secondly, we shift our attention from average to short-term performance, with again a focus on the impact of traffic granularity. In particular, we explore the relation between the level of traffic aggregation and its variability, which directly affects short-term routing performance. Our investigation relies on traffic traces collected from an operational network, and its results provide insight into the cost-performance trade-off associated with deploying “traffic aware” routing protocols.

Traffic management and network control using collaborative on-line simulation

Abstract: The complexity and dynamics of the Internet is driving the demand for scalable and effective network control This paper proposes a collaborative on-line simulation architecture to provide pro-active and automated control functions for networks The general model includes autonomous on-line simulators which continuously monitor/model the network conditions and execute a search in the parameter state space for better settings of the protocol parameters The protocol parameters are then tuned by the on-line simulation system We describe the building blocks of this architecture and investigate the implementation challenges in the areas of network modeling, on-line simulation and parameter search We also discuss the applicability of this system and present the simulation and test results of a preliminary implementation

Auto control of network monitoring and simulation

Abstract: In response to an automatic baseline input, a default control template for a site in a telecommunications network is translated into monitoring and simulation templates. Current end-to-end application and component information are translated into operational modes for monitoring and simulation modules according to the monitoring and simulation templates. Operational controls are established for controlling the monitoring and simulation modules for controlling, in real time, the transmission of network management and simulation traffic.

Network fault analysis tool

Abstract: A testing tool for Internet Service Provider (ISP) network engineers which is used to diagnose network faults, characterize network performance and evaluate new equipment and software releases. The tool can be used to schedule and run proactive tests to identify network problems before subscribers are affected. Further, the tool can be used to provide testing on demand to quickly isolate the root cause of a problem identified by the tool or by network management systems or subscribers. The tool is topology independent and thus does not have to be reconfigured as the network changes. The tool only sends traffic as directed by the network engineer and thus does not generate undesirable heavy network traffic loads, unless such a heavy network loads are desired by the network engineer.

System and method for monitoring data traffic on a network

Abstract: The present invention provides a network monitoring device that monitors a network in order to gather information on the traffic flow generated by network users over the network. The network monitoring device can subsequently distribute network traffic information to subscribers. As the network traffic information is gathered, the network monitoring device can further analyze the information to discern patterns in the traffic flows. A large network service provider with access to network traffic data from a large population of network end-users and business servers can use the network traffic data to obtain information on various patterns in the network traffic data flow and related business interests in real-time.

Real time traffic engineering of data-networks

Abstract: A method and system of providing for central control and intelligent routing of data network traffic where a server (110) is operatively connected to a network (100) and is capable of receiving information regarding network status, specifically capable of recognizing network congestion, formulating a solution to the network congestion and re-configure network traffic to reroute around network congestion.

Stochastic Model for Multilane Traffic Effects on Bridges

Abstract: Traffic loads are the most important variables to be accounted for in designing road bridges. In modern approaches, the target and design values for traffic effects on bridges are obtained through suitable stochastic traffic models processing recorded traffic data. To this end, several theoretical and numerical stochastic models have recently been proposed. Despite their elegance, theoretical models often have limited fields of application, while numerical models, particularly efficient when single-lane traffic flow is considered, turn out to be unsatisfactory when traffic in several lanes, or a combination of traffic actions with those from other sources must be dealt with. This paper presents a more general theoretical stochastic traffic model, which is able, not only to reproduce actual traffic, but to account for such traffic interactions as well. The model, based on an equilibrium renewal process of vehicle arrivals, can be used in all cases where sophisticated evaluation of real traffic effects is required, such as calibration of conventional load models in bridge codes, assessment of existing bridges, as well as the design and analysis of bridges with unusual static structures or subjected to particular traffic conditions. The efficiency of the model is illustrated through meaningful applications.

Method and apparatus for managing aggregate bandwidth at a server

Abstract: A method, apparatus, and computer implemented instructions for managing traffic in a network data processing system. Traffic for a plurality of network paths is monitored. In response a packet for a particular network path within the plurality of network paths causing traffic for the particular network path to exceed a level of traffic allowed, an amount of available bandwidth is reduced based on a fair share for the particular network path.

Simulation optimization of airline delay with constraints

Abstract: Air traffic delay is a growing and expensive problem. We investigated ways to reduce the cost and magnitude of such delays by trading gate delays against more expensive air delays. Air management and planning at this level can be facilitated by simulation, especially for strategies that alter controls on the system. We used the SIMMOD air traffic simulation to model the system. The objective was to determine a set of control measures that achieve the best system performance subject to restrictions on the decision parameters and selected system output measurements. Because observed system performance is "noisy," the problem is a constrained stochastic optimization problem with nonlinear objective function and nonlinear, stochastic constraints, which requires efficient stochastic optimization methods for its solution. Our approach used the simultaneous perturbation stochastic approximation (SPSA) algorithm with a penalty function to handle the difficult constraints.

Hardware and software considerations for implementing hardware-in-the loop traffic simulation

Abstract: Digital computer simulation provides an important tool for the study of complex systems. When the complexity of the problem is too large to warrant an analytical solution, simulation is the only option to analyze system configurations or operational modes prior to their implementation in the field. Not all components in a complex system can be modelled in adequate detail in computer simulations: for example, only simple, generic models of traffic controllers are available. Real-time hardware-in-the-loop simulation allows real traffic controllers to interact with computer simulations to improve accuracy. This paper provides an overview of real-time simulation and then discusses hardware and software constraints to implementing a controller interface device (the NIATT CID II) for real-time hardware-in-the-loop simulation.

Traffic modeling of a sub-network by using ARIMA

Abstract: The Internet traffic characteristics of a sub-network are analyzed from the correlation point of view. It is easy to recognize that the traffic histogram of the sub-network shows the seasonal variation phenomenon with a 24-hour period due to the daily usage. This property is important for traffic modeling. The autoregressive integrated moving average (ARIMA) model is applied to characterize the properties of sun-network traffic. The modeling performance is evaluated by examining the match of histogram and moving average behavior. Our experimental results illustrate that the proposed model can effectively capture the characteristics of Internet traffic and can then be used as a suitable traffic model for the analysis of Internet performance.

Rate control of elastic connections competing with long-range dependent network traffic

Abstract: Long-range dependence is regarded as a fundamental property of network traffic. Using an original approach, we incorporate this property in a traffic control mechanism for elastic connections that can adapt to the instantaneous network load in a differentiated services-type framework. In this scenario, the network makes predictions of bandwidth requirements of the high-priority traffic and returns feedback information to the elastic source. We include a prediction compensation algorithm that compensates for the larger prediction errors for connections with longer roundtrip delay, and analyze the performance of this algorithm. The specific topology involved in traffic control for differentiated services is thus harnessed, together with the long-range dependence, to improve network performance, thereby counteracting the undesirable characteristics of self-similarity. Furthermore, an adaptive version of the rate-based control algorithm is studied, based on the use of real-time estimates of traffic parameters, including the mean, variance, and Hurst parameter.