Required service rate for mixed traffic

В данной работе нами получены границы для скорости обслуживания при некоторых ограничениях на характеристики обслуживания в неоднородной модели входящего трафика, основанной на сумме независимых фрактального броуновского движения и симметричного $\alpha$-устойчивого движения Леви с разными коэффициентами Херста $H_1$ и $H_2=1/\alpha$. Хорошо известно, что для процессов, приращения которых имеют тяжёлые хвосты, методы расчета эффективной пропускной способности, основанные на производящей функции моментов входящего потока, не применимы. Однако существуют простые соотношения между характеристиками потока, скоростью обслуживания $C$ и вероятностями $\varepsilon(b)$ переполнения для конечного и бесконечного буфера, из которых при фиксированном значении $\varepsilon(b)$ можно выразить $C$. In this paper we analyse the nonhomogenous traffic model based on sum of independent Fractional Brownian motion and symmetric $\alpha$-stable Levy process with different Hurst exponents $H_1$ and $H_2=1/\alpha$ and present bounds for the required service rate under QoS constraints. It is well known that for the processes with long-tailed increments effective bandwidths are not expressed by means of the moment generating function of the input flow. However we can derive simple relations between the flow parameters, service rate $C$ and overflow probabilities $\varepsilon (b)$ for finite and infinite buffer. In this way it is possible to find required service rate $C$ under a constraint on maximum overflow probability.

DELAY MODELS BASED ON SYSTEMS WITH USUAL AND SHIFTED HYPEREXPONENTIAL AND HYPERERLANGIAN INPUT DISTRIBUTIONS

Context. In the queueing theory, the study of systems with arbitrary laws of the input flow distribution and service time is relevant because it is impossible to obtain solutions for the waiting time in the final form for the general case. Therefore, the study of such systems for particular cases of input distributions is important. Objective. Getting a solution for the average delay in the queue in a closed form for queuing systems with ordinary and with shifted to the right from the zero point hyperexponential and hypererlangian distributions in stationary mode. Method. To solve this problem, we used the classical method of spectral decomposition of the solution of the Lindley integral equation. This method allows to obtaining a solution for the average delay for two systems under consideration in a closed form. The method of spectral decomposition of the solution of the Lindley integral equation plays an important role in the theory of systems G/G/1. For the practical application of the results obtained, the well-known method of moments of probability theory is used. Results. For the first time, a spectral decomposition of the solution of the Lindley integral equation for systems with ordinary and with shifted hyperexponential and hyperelangian distributions is obtained, which is used to derive a formula for the average delay in a queue in closed form. Conclusions. It is proved that the spectral expansions of the solution of the Lindley integral equation for the systems under consideration coincide; therefore, the formulas for the mean delay will also coincide. It is shown that in systems with a delay, the average delay is less than in conventional systems. The obtained expression for the waiting time expands and complements the wellknown incomplete formula of queuing theory for the average delay for systems with arbitrary laws of the input flow distribution and service time. This approach allows us to calculate the average delay for these systems in mathematical packages for a wide range of traffic parameters. In addition to the average waiting time, such an approach makes it possible to determine also moments of higher orders of waiting time. Given the fact that the packet delay variation (jitter) in telecommunications is defined as the spread of the waiting time from its average value, the jitter can be determined through the variance of the waiting time.

MATHEMATICAL DELAY MODEL BASED ON SYSTEMS WITH HYPERERLANGIAN AND ERLANGIAN DISTRIBUTIONS

Context. Studies of G/G/1 systems in queuing theory are relevant because such systems are of interest for analyzing the delay of data transmission systems. At the same time, it is impossible to obtain solutions for the delay in the final form in the general case for arbitrary laws of distribution of the input flow and service time. Therefore, it is important to study such systems for particular cases of input distributions. We consider the problem of deriving a solution for the average queue delay in a closed form for two systems with ordinary and shifted hypererlangian and erlangian input distributions. Objective. Obtaining a solution for the main characteristic of the system – the average delay of requests in the queue for two queuing systems of the G/G/1 type with ordinary and with shifted hypererlangian and erlangian input distributions. Method. To solve this problem, we used the classical method of spectral decomposition of the solution of the Lindley integral equation. This method allows to obtaining a solution for the average delay for systems under consideration in a closed form. The method of spectral decomposition of the solution of the Lindley integral equation plays an important role in the theory of systems G/G/1. For the practical application of the results obtained, the well-known method of moments of probability theory is used. Results. For the first time, spectral expansions of the solution of the integral Lindley equation for two systems are obtained, with the help of which calculation formulas for the average delay in a queue in a closed form are derived. Thus, mathematical models of queuing delay for these systems have been built. Conclusions. These formulas expand and supplement the known queuing theory formulas for the average delay G/G/1 systems with arbitrary laws distributions of input flow and service time. This approach allows us to calculate the average delay for these systems in mathematical packages for a wide range of traffic parameters. In addition to the average delay, such an approach makes it possible to determine also moments of higher orders of waiting time. Given the fact that the packet delay variation (jitter) in telecommunications is defined as the spread of the delay from its average value, the jitter can be determined through the variance of the delay.

Modelling of the flow in front of the jet obstacle at variation of oncoming flow parameters

The results of numerical simulation of the problem of interaction of supersonic flow with a jet obstacle under variation of input flow parameters are considered. The problem is solved in the system of Navier-Stokes equations. Laminar flows are considered. The qualitative flow pattern has been studied under the variation of incoming flow velocity and boundary layer thickness in the incoming flow. The calculations were performed using the OpenFOAM software package.

Mass transfer in a vertical cylindrical inert granular layer for axial flow input

Based on pseudodiffusion model with orthotropic tensor of the dispersion of the tools analyze the impact of heterogeneity of the mass flow of the substance entering the working area of the device with stationary cylindrical granular inert layer of non-stationary boundary value problems for linear differential equations in private derivatives of parabolic type with initial conditions corresponding to the device, leveling heterogeneity. The analytical solution of the formulated problem is obtained by successive application of the semi-bounded integral Laplace transform and the finite integral Hankel transform, are verified the structures of functions describing the input flow as a result of using equalizing systems (distribution grids and scattering disks). Computational experiments allowed us to quantitatively describe the picture of heterogeneity of concentration fields depending on the values of the flow dispersion coefficients and the type of device that equalizes the input flow. It is shown that without equalizing elements, the input stream creates a significant heterogeneity of the concentration field in the apparatus, and the disk has the highest efficiency in this aspect compared to the lattice due to the formation of a more "smooth" input concentration profile. A specific example of evaluating the heterogeneity of concentration fields in the complex cleaning unit of an air separation unit showed the effectiveness of the proposed approach.