Nonstationary analysis of the loss queue and of queueing networks of loss queues

We present an iterative scheme based on the fixed-point approximation method, for the numerical calculation of the time-dependent mean number of customers and blocking probability functions in a nonstationary queueing network with multi-rate loss queues. We first show how the proposed method can be used to analyze a single-class, multi-class, and multi-rate nonstationary loss queue. Subsequently, the proposed method is extended to the analysis of a nonstationary queueing network of multi-rate loss queues. Comparisons with exact and simulation results showed that the results are consistently close to the exact results and they are always within simulation confidence intervals.     

Spectrometrie de Masse—VIII: Elimination D'eau Induite par Impact Electronique Dans le Tetrahydro-1,2,3,4 Naphtalenediol-1,2

Electron-impact-induced loss of a water molecule is an important fragmentation pattern of 1,2,3,4-tetrahydronaphthalene-1,2-diol. From deuterium labelling experiments the hydroxylic hydrogen atoms are shown to participate to over 70% in the water elimination. On the other hand, the C-4 hydrogen atoms are involved to the extent of 18% in this sequence. Statistical distribution, resulting from the randomisation of various hydrogen atoms, has been calculated and compared to the experimental values.     

Mass spectrometric study of conjugated bifunctional acetylenes: 2—Ynals and ynones

This study is based on results obtained by new techniques for observing metastable ions which make it possible to determine the fragmentation paths of conjugated ynals and ynones. For the ynals, the most interesting fragment is the [M–28]⁺˙ ion. For the ynones, when a McLafferty rearrangement is feasible, the ion arising therefrom is more abundant than the [M? CO]^+. ion. However, this elimination of a neutral CO molecule is quite important for the true acetylene ketones.     

Performance analysis of limited-range wavelength conversion in an OBS switch

We compute analytically burst blocking probabilities in an OBS switch when limited-range wavelength conversion is employed. Two separate queueing models are proposed and analyzed approximately; one for the case where the degree of conversion d is 1 or 2, another for large values of d. The arrival process of bursts is assumed to be an IDLE-ON process. The accuracy of these queueing models was tested against simulation. We show numerically that in order to keep the burst blocking probability within an acceptable level, the utilization of each wavelength has to be low.     

Approximate analysis of arbitrary configurations of open queueing networks with blocking

An algorithm for analyzing approximately open exponential queueing networks with blocking is presented. The algorithm decomposes a queueing network with blocking into individual queues with revised capacity, and revised arrival and service processes. These individual queues are then analyzed in isolation. Numerical experience with this algorithm is reported for three-node and four-node queueing networks. The approximate results obtained were compared against exact numerical data, and they seem to have an acceptable error level.Supported in part by a grant from CAIP Center, Rutgers University.Supported in part by the National Science Foundation under Grant DCR-85-02540.     

Trustworthy Web services provisioning for differentiated customer services

With the number of e-Business applications dramatically increasing, a service level agreement (SLA) will play an important part in Web services. The SLA is a combination of several quality of services (QoS), such as security, performance, and availability, agreed between a customer and a service provider. Most existing research addresses only one of these QoS metrics. Furthermore, in the case of the response time defined as one of QoS metrics for performance, only the average time to process and complete a job is typically used. Moreover, customer requests often need to be distinguished, with different request characteristics and customer’s different service requirements. In this paper, we consider a set of computer resources used by a service broker to host enterprise applications for two classes of differentiated customer services subject to a service level agreement. We study three QoS metrics, namely, trustworthiness, a percentile response time, and availability. The percentile response time metric defines a value below which the end-to-end response time has to be for a given percent of time. We present an approach for resource optimization in such an environment that minimizes the total cost of computer resources while satisfying all these three QoS metrics in a trust-based resource provisioning problem which typically arises in Web services. We formulate the trust-based resource provisioning problem as an optimization problem under SLA constraints, and then solve it using an efficient numerical procedure.     

Bandwidth provisioning in ADSL access networks

We consider an ADSL access network consisting of subscribers, digital subscriber line access multiplexers (DSLAMs), metro Ethernet switches and a broadband remote access aggregation server (BRAS). We obtain expressions for dimensioning the access network in the upstream direction. Specifically, we show that the bandwidth required at each DSLAM, metro Ethernet switch, and BRAS can be expressed as an exponential function of the subscribers in a log scale when the number of subscribers does not surpass a certain value. After this value, it grows linearly as a function of the subscribers. Copyright © 2009 John Wiley & Sons, Ltd.     

Computing blocking probabilities in multiclass wavelength-routingnetworks with multicast calls

We present an approximate analytical method to compute efficiently the call-blocking probabilities in wavelength-routing networks with multiple classes of both unicast and multicast calls. Our approach involves the following steps. We start with an approximate solution to a linear single-class unicast network which we developed earlier. Next, all classes of calls on a particular route are aggregated to give an equivalent single-class model. We then extend the path decomposition algorithms that we have developed for single-class networks to handle mesh networks with multiple classes of calls. We show how to use these path decomposition algorithms to decompose large networks with multicast paths into smaller subsystems with only linear paths, which, in turn, are solved by the product-form approximation algorithm. We also consider a state-dependent Poisson arrival process for multicast calls which is more accurate in capturing the behavior of these calls     

Hierarchical Queue Networks with Partially Shared Servicing

The queue network studied consists of n infinite queues in parallel served by independent servers and by other servers all linked to form a hierarchical structure. The total service a unit receives depends partially on other units in service. We call this type of servicing partially shared servicing. All interarrival times as well as service times are assumed exponentially distributed. The characteristic of interest is the traffic intensity of the infinite queues. Some simple formulae are obtained. An application to modelling a disc I/O system is described. The model turns out to be useful and accurate with wide applicability.     

New off-line aircraft instrumentation for non-methane hydrocarbon measurements

New off-line instrumentation was developed to implement measurements of non-methane hydrocarbons (NMHC) on (French) research aircraft. NMHC are collected on multisorbent tubes by AMOVOC (Airborne Measurements Of Volatile Organic Compounds), a new automatic sampler. AMOVOC is a versatile and portable sampler targeting a wide range of NMHC at high frequency (sampling time of 10 min). Multisorbent tubes are analyzed on the ground by short-path thermal desorption coupled with gas chromatography and mass spectrometry. The development and optimization of both NMHC sampling and analysis are reported here. On the one hand, the paper points out technical choices that were made according to aircraft constraints and avoiding sample loss or contamination. On the other hand, it describes analytical optimization, tube storage stability, and moisture removal. The method shows high selectivity, sensitivity (limit of detection less than 10 ppt) and precision (less than 24%). Finally, NMHC data collected on French aircraft during the African Monsoon Multidisciplinary Analysis campaign are reported for the first time. The results highlight instrumentation validity and protocol efficiency for NMHC measurements in the lower and upper troposphere.