Showing papers on "Network traffic simulation published in 1984"

Investigation of network-level traffic flow relationships: some simulation results

Abstract: Results of an exploratory study of networklevel relationships in an isolated network with a fixed number of vehicles circulating according to the microscopic rules embedded in the NETSIM traffic simulation model are presented. The primary concern was to assess the usefulness of such simulation-based approaches in the investigation of macroscopic network-level traffic relationships. Three specific objectives were addressed: (a) identification of network-level descriptors that are related in operationally useful and simple ways, (b) exploration of some aspects of the two-fluid theory of town traffic, and (c) examination of the traffic flow distribution over the network components. A number of simulations were conducted on the same network under two different sets of control schemes and traffic characteristics at widely varying vehicle concentrations. The results were analyzed with respect to the three objectives, yielding useful insights into network-level traffic phenomena and suggesting promising avenues for further research.

Dynemo: a model for the simulation of traffic flow in motorway networks

Abstract: The paper presents the simulation model dynemo which has been designed for the development, evaluation and optimization of traffic control systems for motorway networks. A new traffic flow model included with the simulation package combines the advantages of a macroscopic model (computational simplicity) with the advantages of a microscopic model (output statistics relating to individual vehicles). For each stretch in the network, the model needs as input a relationship between traffic density and mean speed and the distribution of free flow speeds. The new traffic flow model is validated by use of an example. The simulation package is implemented on a 16-bit microcomputer. A real network with a traffic control system has been simulated with the model. (Author/TRRL)

A common network flow formulation for several civil engineering problems

Abstract: This paper discusses a common network flow problem that arises in four areas of civil engineering. The problem is one of identifying arc flows that simultaneously satisfy the circuit and node law constraints for a given network. Applications and computational procedures in the areas of elastic structural analysis, hydraulic network analysis, traffic equilibrium and construction task scheduling are described. The interpretation of decision variables and mathematical functions will vary depending on the application, but the general priblem formulation and solution technique for each application remains essentially unchanged. Analogies between the different applications may enhance the conceptual understanding and intuition of engineers working in each area.

Simulation output analysis for local area computer networks

Abstract: This paper develops discrete event simulation methods for local area computer networks. We restrict attention to local network simulations with an underlying stochastic process that can be represented as a generalized semi-Markov process. Using a “geometric trials” criterion for recurrence, we establish a regenerative process structure for passage times in this setting. This leads to an estimation procedure for delay characteristics of ring and bus networks.

Empirical Analysis of a Token Ring Network

Abstract: : The purpose of this project was to do an empirical study of the performance, reliability and traffic patterns of the Laboratory for Computer Science version two local area network Performance data allows the comparison of the version two ring specifically and token ring networks in general with other local area network strategies, such as the Ethernet, to discover which type of local area network is decidedly better and why Traffic patterns indicate how computer networks are used Perfomance analysis can be performed both theoretically and experimentally Mathematical analysis of a local area network is complex and only roughly approximates the behavior of a network Mathematical analysis is useful for determining which systems might be usable, but does not give enough information to choose among the different systems Network data refines mathematical models for network evaluation Improved mathematical models make evaluation and simulation of networks before construction more practical Empirical analysis determines the performance of an network Not only can the network traffic be evaluated, but also network properties can be determined Reported traffic on a local area network can improve mathematical models of traffic for theoretical evaluation and also suggest the traffic handling properties that a local area network and its hosts should have

Traffic access control strategies in integrated service digital networks

Abstract: It has become a truism recently that the field of modern Telecommunications is undergoing a universal evolution: The evolution toward an Integrated Service Digital Network, or ISDN for handling the multifarious data transmission requirements of the future. Given the expected increasing need to transmit, simultaneously on one channel, a variety of data types (graphics, video, etc.) in addition to the ubiquitous voice, it becomes extremely important to study the problem of controlling access of these different traffic types efficiently and equitably onto the network. This integrated access control problem is identified in this thesis as an important part of an ISDN, and formulated under different traffic environments. Then, the thesis proposes, analyzes, and compares various traffic access control, or multiplexing, schemes for suitable use in each configuration of this ISDN environment. The access schemes considered for a homogeneous circuit/packet traffic environment show that a balanced trade-off in circuit-packet performance versus fairness among users can be achieved by restricting sharing of the circuit bandwidth among these users. In a heterogeneous circuit/packet traffic configuration, the packet access delay may exhibit excessive surges caused by the multiband circuit process. The problem of controlling packet access is formulated as a constrained nonlinear programming problem. The resulting optimum packet control is shown to be delay-bound and easily implementable by a finite buffer. For the case of multiplexing streams of heterogeneous all-blocked traffic we introduce a class of Restricted Access (RA) strategies whereby access restrictions are judiciously set on selected groups of traffic types. It is shown that RA policies can be optimally designed, and are capable of improving system performance significantly. Access restrictions are also employed in multiplexing a mixture of queueable and nonqueueable traffic types. Blocking/queuing multiplexing schemes are considered for this configuration, and analyzed for the case of a blockable wideband (WB) traffic type and a queueable narrowband (NB) traffic type. It is shown that an adaptive control strategy, switching from one scheme to another according to the offered load, yields best combined performance. In multiplexing all-queued multiband traffic, the access problem becomes one of finding a queue service discipline that packs waiting requests efficiently and equitably onto the channel. Several appealing service policies are proposed and analyzed mathematically and/or by simulation. In particular, our assessments of the relative performance of the different policies studied make us advocate the easily implementable FIFO policy as a sound policy for practical use.

The discrete event simulation computer - DESC

Abstract: Simulation of large models on digital computers is often limited by the high computational expenses. The Discrete Event Simulation Computer (DESC) reported here improves simulation performance through an exploitation of parallelism inherent in simulation, with regard to list processing, random number generation, statistical analysis and program control. The DESC consists of a set of nodes that communicate via FIFO-buffered channels (i.e. do not share memory among nodes). In order to achieve high system throughput dedicated hardware modules were developed; this includes new concepts for a list processor and a hardware random number generator for uniform deviates.The implementation of simulation languages such as SIMULA, SIMSCRIPT or GPSS is conceptually straightforward. We chose SIMULA as the frame language concept. Metrics applicable to simulation throughput and simulation costs are defined and compared with the CD CYBER 175.