We present an analysis of the arrival process for world-wide web (WWW) request traffic at the hypertext transfer protocol (HTTP) level. Examination of three separate HTTP traffic datasets shows that the arrival process of HTTP request packets is not Poisson and does not appear to be tending towards Poisson as the number of aggregated traffic sources increase. Based on statistical comparison with common probability distributions we postulate a model for HTTP request traffic with lognormally distributed interarrival times and an invariant shape parameter of 1.0. However, a simulation study indicates that the estimate of response time performance for a WWW proxy server is insensitive to the choice of our model of lognormally distributed HTTP request interarrival times in place of the Poisson arrival process assumption.
Proc. SPIE. 2417, Multimedia Computing and Networking 1995
KEYWORDS: Defense and security, Networks, Local area networks, Multimedia, Computer architecture, Network architectures, Prototyping, Standards development, Asynchronous transfer mode, Voltage controlled current source
This paper describes the software architecture for the ATM network interface of a prototype multimedia terminal. The terminal is designed to support continuous media and data communications over a low speed ATM network and is based on a UNIX workstation connected to a commercial ATM LAN. The interface architecture addressed complex multimedia call handling, quality of service (QoS) and resource allocation issues. The terminal will be used to investigate methods for handling degradation in QoS on defence ATM networks incorporating low speed network links where QoS is time variant.
This paper presents a comparison between two different optical geometries used in Fourier Transform Profilometry (FTP); crossed- optical-axes geometry and parallel-optical-axes geometry. A mathematical proof is presented to demonstrate that parallel- optical-axes geometry can provide a wider range of measurement than crossed-optical-axes geometry. The FTP method decodes the 3- D shape information from the phase information stored in a 2-D image of the object onto which Ronchi grating is projected. The phase information can be separated from the image signal by two methods; the phase subtraction method and the spectrum shift method. An experimental comparison between two phase extraction methods is presented. The results show that the phase subtraction method is less susceptible to nonlinearity of recording media and systematic optical geometry error. On the other hand, the spectrum shift method is faster in terms of computing time and noise immune. The experimental comparison also demonstrates a noise immune phase unwrapping strategy, based on a minimum spanning tree approach, to form a contiguous map of the object surface.
This paper describes the application of digital Fourier transform to phase encoded intensity distribution. Attention is drawn to a method of extracting quantitative information automatically from the interferometric fringe data. To achieve this a set of carrier fringes has been added to interferometric fringe data. This has made it possible to form a phase map using a FFT (Fast Fourier Transform) algorithm. A Minimum Spanning Tree (MST) phase unwrapping strategy has been used to create a contiguous map of the whole fringe field. Finally, the measurement parameter related to the fringe field has been calculated from one single image. Experimental results are given for the burner flames, a compressible flow, and photoelastic fringe data.
A carrier fringe technique for measuring surface deformation is described and verified by experiments. In contrast to conventional holography and fringe analysis, this holographic system is based on fiber optics and automatic spatial carrier fringe pattern analysis techniques. Single-mode optical fibers are used to transfer both the object and reference beams. Carrier fringes are generated by simply translating the object beam between two exposures. The fast Fourier transform method is used to process the interferograms. The experiment gives an example of the tile-level minimum spanning tree phase unwrapping technique and introduces a new pixel-level noise immune unwrapping strategy also based on minimum spanning trees. The test object is a centrally loaded disk. An excellent correlation between the theoretical deformation profile and that suggested by the technique is given.
Application of particle image velocimetry (PIV) to a scale transonic wind tunnel and to a cold burner spray is described. It is shown that diffraction limited imaging makes it possible to extend the working range of PIV systems to several meters enabling a broad variety of industrial applications and to determine particle sizes with a high magnification objective. In both cases diffraction limited imaging significantly reduced the laser energy required to form satisfactory particle images. Particle images were recorded onto 35 mm film and a CCD video camera.
This paper describes a carrier fringe technique for measuring surface deformation. In contrast to conventional holography and fringe analysis, this holographic system is based on the fiber optics and automatic spatial carrier fringe pattern analysis techniques. Carrier fringes are generated by simply translating the object beam between two exposures. Single-mode optical fibers are used to transfer both the object and reference beams. The use of optical fibers offers advantages in the field of optical holography. The fast Fourier transform (FFT) method is used to process the interferograms. This method of fringe pattern analysis is a successful technique for extracting phase information from fringe patterns which result from the interference of tilted wavefronts. The paper also introduces the tile level, minimum spanning tree and phase unwrapping techniques. The method is illustrated by measuring the centrally loaded disk. A correction is made for the nonuniform spacing of the carrier fringes, which was introduced by a slight inclination of the object. The results are given for disk, including the perspective plot of the out-of-plane deformation field, the maps of wrapped and unwrapped phase, and a contour map of the unwrapped phase.
A new method for extracting quantitative information from a double exposure holographic interferogram is presented. Dual reference beams are used to produce continuously variable phase differences between the two images of the object at the recording stage of the hologram. Image reconstruction at three known phase differences, via a CCD camera and digital framestore, allow new automatic image processing methods to calculate the three-dimensional surface deformation.
The present light sheet system for 3D studies of the location and structure of transonic flows employs a CCD video camera and digital frame-store which are synchronized with the pulsed laser so that the resulting images can be immediately displayed via microcomputer. These video images are digitally enhanced in order to display 3D coordinate data. An illustrative demonstration of the system is for rotating transonic-jet flow. The visualized images show instantaneous transonic flow structures.