Priority queueing strategies and buffer allocation protocols fortraffic control at an ATM integrated broadband switching system

The problem of furnishing an asynchronous transfer mode (ATM) based broadband-ISDN (B-ISDN) with two bearer services supporting different grades of transfer quality is addressed. The focus is on priority bandwidth and buffer management in the ATM communications nodes (switches, multiplexers or concentrators, and expanders) in the context of a multichannel network architecture. Detailed queueing analyses and simulations and results are provided to evaluate the differentiation between traffic classes that can be achieved by different strategies. The implementation complexity of the different schemes is discussed. Various priority queueing strategies characterized mainly by different degrees of resource sharing and a general system model for performance evaluation are introduced. Performance comparisons and design tradeoffs are addressed     

AUTOMATIC ANALYSIS OF HOP RESINS BY ION EXCHANGE CHROMATOGRAPHY

Ion exchange chromatography has been used to provide a quantitative automatic analysis of lupolunes, humulones, humulinic acid, iso-α-acid and hulupones. The resins are extracted and chromatographed on a column of Q.A.E. Sephadex in the acetate form, using an acetic acid gradient in methanol as eluent. The absorbance of the effluent is recorded and the peaks are integrated. A comparison of peak areas with known standards gives a quantitative analysis of the hop components. The analysis takes I h if only the α and β resins are required, 2 h for an analysis including iso-α-acid and h if hulupone is included. The method is applicable to hops, hop extracts, wort and beer.     

Hot-wire chemical vapor deposition of WO3−x thin films of various oxygen contents

We present the synthesis of tungsten oxide (WO_3−x) thin films consisting of layers of varying oxygen content. Configurations of layered thin films comprised of W, W/WO_3−x, WO₃/W and WO₃/W/WO_3−x are obtained in a single continuous hot-wire chemical vapor deposition process using only ambient air and hydrogen. The air oxidizes resistively heated tungsten filaments and produces the tungsten oxide species, which deposit on a substrate and are subsequently reduced by the hydrogen. The reduction of tungsten oxides to oxides of lower oxygen content (suboxides) depends on the local water vapor pressure and temperature. In this work, the substrate temperature is either below 250 °C or is kept at 750 °C. A number of films are synthesized using a combined air/hydrogen flow at various total process pressures. Rutherford backscattering spectrometry is employed to measure the number of tungsten and oxygen atoms deposited, revealing the average atomic compositions and the oxygen profiles of the films. High-resolution scanning electron microscopy is performed to measure the physical thicknesses and display the internal morphologies of the films. The chemical structure and crystallinity are investigated with Raman spectroscopy and X-ray diffraction, respectively.     

A reconfigurable ATM switch fabric for fault tolerance and trafficbalancing

A large-scale asynchronous transfer mode (ATM) switch fabric that can be constructed with currently feasible technology is proposed. Based on analysis of the technology, it is found that module interconnection becomes the bottleneck for a large fast packet switch. Fault tolerance for the switch is achieved by dynamic reconfiguration of the module interconnection network. The design improves system reliability with relatively low hardware overhead. An abstract model of the replacement problem for the design is presented, and the problem is transformed into a well-known assignment problem. The maximum fault tolerance is found, and a fast replacement algorithm is given. The reconfiguration capability can also be used to ameliorate imbalanced traffic flows. The authors formulate this traffic flow assignment problem for the switch fabric and show that the problem is NP-hard. A simple heuristic algorithm is proposed, and an example is given     

Permutation rules for simplex finite elements

Simplicial finite elements have many symmetries, which are commonly exploited in programs to save computing time and storage. All possible permutations of the interpolation functions of an N-simplex can be expressed in terms of N basic permutation operations. The relevant permutation matrices are given for triangles up to order 20 and tetrahedra up to order 10.     

An approximate model for performance evaluation of real-time multimedia communication systems

A Markov Modulated Poisson Process (MMPP) is a doubly stochastic Poisson process which has recently received a lot of attention due to its ability to model a highly correlated arrival stream while retaining analytical tractability. In this paper, the cell arrival process from integrated voice and data sources is approximated by a two-state MMPP with batch arrivals (BMMPP). We propose a new matching technique which leads to more accurate performance prediction than other recent work for both delay estimation and evaluation of tail probabilities. While using BMMPP in the model does not noticeably increase the computational complexity over MMPP, it allows better representation of traffic sources with significantly higher burstiness. Another major contribution of the proposed model is its simplicity which makes the model suitable for real-time traffic control. An extended version of the model for integrated video, voice and data sources is also given with numerical examples again showing that the accuracy is quite satisfactory.     

Finite element analysis of inductive strips in unilateral finlines

A three-dimensional finite-element method (FEM) is used in conjunction with the boundary-marching algorithm to characterize inductive strips in unilateral finlines. For an idealized finline of zero fin thickness, without mounting groove effect, the results agree with those obtained by the hybrid-mode spectral-domain approach to within a few percent with only 98 elements. Field distributions for the dominant propagation mode in unilateral finlines are generated with the boundary-marching algorithm. The effect of metallization thickness, the influence of the mounting groove, and the effect of substrate bending on the discontinuity parameters are studied in detail     

Comments, on `Three-dimensional finite, boundary, and hybridelement solutions of the Maxwell equations for lossy dielectric media'[and reply]

For the original article see ibid., vol.36, no.4, p.682-93 (1988). The commenters point out a potential source of error with the finite-element analysis of the vector wave equation in the paper of K.D. Paulsen, et al. Specifically, this error source is connected with the finding that, if spurious modes exist in the finite-element solution of the eigenvalue problem, the corresponding solution to the externally driven problem may consist of some linear combination of the nonphysical spurious modes in addition to the physical modes. In replying, the author acknowledges the importance of the question of spurious modes