Time Data Services Research Articles

Ordered Packet Length Based Groupwise Transmission Scheme for Rate Scheduling in Burst Switching DS/CDMA System

This paper proposes a new packet rate scheduling scheme for a non-real time data services over the uplink of a burst switching based direct sequence code division multiple access (DS/CDMA) system to support integrated voice/data services. We consider the most general form of optimization problem formulation to determine the optimal number of transmission time groups along with their data rates, which minimizes the average packet transmission delay. An ordered packet length based groupwise transmission (OLGT) scheme is proposed as a simple heuristic solution to this problem, and we present some analytical results for performance comparison with other possible schemes.

Channel-aware priority-based groupwise packet scheduling for non-real time data service with burst-switching DS/CDMA system

The algorithm of scheduling scheme of channel-aware priority-based groupwise transmission is investigated for non-real time data service for the uplink direct sequence code division multiple access (DS/CDMA) system using the burst-switching scheme to support the integrated voice/data service. The proposed scheme optimally determines the transmission-time groups and assigns optimal data rates to the users with packets in the transmission-time group depending on priority metric, which involves several parameters such as delay threshold, waiting time, length of packet, and state of the channel, in a way of minimizing the average transmission delay. Simulation results show that the proposed algorithm gives better performance of average transmission delay and packet loss probability than any other conventional algorithms.

Nonparametric Inference About Service Time Distribution from Indirect Measurements

SummaryIn studies of properties of queues, for example in relation to Internet traffic, a subject that is of particular interest is the ‘shape’ of service time distribution. For example, we might wish to know whether the service time density is unimodal, suggesting that service time distribution is possibly homogeneous, or whether it is multimodal, indicating that there are two or more distinct customer populations. However, even in relatively controlled experiments we may not have access to explicit service time data. Our only information might be the durations of service time clusters, i.e. of busy periods. We wish to ‘deconvolve’ these concatenations, and to construct empirical approximations to the distribution and, particularly, the density function of service time. Explicit solutions of these problems will be suggested. In particular, a kernel-based ‘deconvolution’ estimator of service time density will be introduced, admitting conventional approaches to the choice of bandwidth.

Load-based transmission rate assignment scheme for integrated voice/data DS-CDMA system

A load-based transmission rate (LTR) assignment scheme is proposed for non-real time data services in an integrated voice/data direct sequence code division multiple access (DS/CDMA) system. The LTR scheme optimally determines the transmission rate for each session according to its individual load so as to minimise the overall average packet transfer delay. It is shown that the average packet delay of LTR is significantly lower than that of the conventional traffic-based grouping transmission (TGT) scheme.

Joint power control and intracell scheduling of DS-CDMA nonreal time data

The performance of DS-CDMA systems depends on the success in managing interference arising from both intercell and intracell transmissions. Interference management in terms of power control for real time data services like voice has been widely studied and shown to be a crucial component for the functionality of such systems. In this work we consider the problem of supporting downlink nonreal time data services, where in addition to power control, there is also the possibility of controlling the interference by means of transmission scheduling. One such decentralized schedule is to use time division so that users transmit in a one-by-one fashion within each cell. We show that this has merits in terms of saving energy and increasing system capacity. We combine this form of intracell scheduling with a suggested distributed power control algorithm for the intercell interference management. We address its rate of convergence and show that the algorithm converges to a power allocation that supports the nonreal time data users, using the minimum required power while meeting requirements on average data rate. Numerical results indicate a big potential of increased capacity and that a significant amount of energy can be saved with the proposed transmission scheme.

Waiting-time tail probabilities in queues with long-tail service-time distributions

We consider the standardGI/G/1 queue with unlimited waiting room and the first-in first-out service discipline. We investigate the steady-state waiting-time tail probabilitiesP(W>x) when the service-time distribution has a long-tail distribution, i.e., when the service-time distribution fails to have a finite moment generating function. We have developed algorithms for computing the waiting-time distribution by Laplace transform inversion when the Laplace transforms of the interarrival-time and service-time distributions are known. One algorithm, exploiting Pollaczek's classical contourintegral representation of the Laplace transform, does not require that either of these transforms be rational. To facilitate such calculations, we introduce a convenient two-parameter family of long-tail distributions on the positive half line with explicit Laplace transforms. This family is a Pareto mixture of exponential (PME) distributions. These PME distributions have monotone densities and Pareto-like tails, i.e., are of orderx −r forr>1. We use this family of long-tail distributions to investigate the quality of approximations based on asymptotics forP(W>x) asx→∞. We show that the asymptotic approximations with these long-tail service-time distributions can be remarkably inaccurate for typicalx values of interest. We also derive multi-term asymptotic expansions for the waiting-time tail probabilities in theM/G/1 queue. Even three terms of this expansion can be remarkably inaccurate for typicalx values of interest. Thus, we evidently must rely on numerical algorithms for determining the waiting-time tail probabilities in this case. When working with service-time data, we suggest using empirical Laplace transforms.

Selecting job scheduling algorithms: beta distribution model for service times

Over a decade ago, Leonard Kleinrock developed a model for selecting best–performance scheduling algorithms for computer systems. The M/G/I queuing system used by Kleinrock requires that an estimate of the service–time probability distribution function (p.d.f.) be made in order to derive results. While methods of fitting service–time data to p.d.f.s are available, this paper argues that the use of a generalized beta distribution of the second type (GB2) in concert with the Kleinrock model reduces the need to estimate alternative models and avoids the consequences of arbitrarily imposing invalid assumptions on the data.

An ethernet compatible protocol for real-time voice/data integration

This paper addresses the issues involved in providing an integrated real time voice and data service on the Ethernet local network. The paper proposes a protocol that is functional, robust and compatible with current Ethernet specifications. The proposed voice protocol meets the real time voice performance requirements for local and potentially remote distribution of voice. As demonstrated by detailed simulation, the addition of voice traffic to an existing Ethernet via the proposed protocol improves the total channel utilization and leaves more data-usable bandwidth when compared to the same load of voice being added via CSMA-CD. Controllers implementing this protocol can co-exist on an Ethernet with stations using conventional controllers. Additionally, the introduction of the voice controllers requires no changes to the data link procedures used by the already existing data stations in the network. The protocol can be considered for other real time applications, such as process control, as well.

A note on mixed exponential approximations for Gi/G/1 waiting times

A method is offered for the effective estimation of the stationary waiting-time distribution of the GI/G/1 queue by a (possibly nonconvex) mixed exponential CDF. The approach relies on obtaining a generalized exponential mixture as an approximation for the distribution of the service times. This is done by the adaptation of a nonlinear optimization algorithm previously developed for the maximum-likelihood estimation of parameters from mixed Weibull distributions. The approach is particularly well-suited for obtaining the delay distribution beginning from raw interarrivai and service-time data.