Long-range dependence and heavy-tail modeling for teletraffic data

The analysis and modeling of computer network traffic is a daunting task considering the amount of available data. This is quite obvious when considering the spatial dimension of the problem, since the number of interacting computers, gateways and switches can easily reach several thousands, even in a local area network (LAN) setting. This is also true for the time dimension: Willinger and Paxson (see Ann. Statist., vol.25, no.5, p.1856-66, 1997) cite the figures of 439 million packets and 89 gigabytes of data for a single week record of the activity of a university gateway in 1995. The complexity of the problem further increases when considering wide area network (WAN) data. In light of the above, it is clear that a notion of importance for modern network engineering is that of invariants, i.e., characteristics that are observed with some reproducibility and independently of the precise settings of the network under consideration. In this tutorial article, we focus on two such invariants related to the time dimension of the problem, namely, long-range dependence, or self-similarity, and heavy-tail marginal distributions     

CCITT work in teletraffic engineering

The advantages and drawbacks of standardization in TTE (teletraffic engineering) are examined. It is pointed out that the TTE recommendations of CCITT are intended to be international standards. Unlike signaling systems, interfaces, or protocols, the necessity for standardization in this area is not self-evident. However, standardization of grade of service (GOS) definitions, values, and relevant reference conditions seems to be necessary. Support for engineering methods also offers advantages. TTE-related activities in different CCITT study groups try to satisfy many often contradictory demands. Trends in telecommunications strongly support the view that concentration of TTE studies in CCITT would be desirable     

Change detection in teletraffic models

We propose a likelihood-based ratio test to detect distributional changes in common teletraffic models. These include traditional models like the Markov modulated Poisson process and processes exhibiting long range dependency, in particular, Gaussian fractional ARIMA processes. A practical approach is also developed for the case where the parameter after the change is unknown. It is noticed that the algorithm is robust enough to detect slight perturbations of the parameter value after the change. A comprehensive set of numerical results including results for the mean detection delay is provided     

一种基于FGN和IDFT的自相似通信量生成算法

对网络模拟中必需的自相似通信量生成方法进行了研究,提出了一种基于分数高斯噪声(FGN,fractionalGaussiannoise)过程和逆离散傅立叶变换(IDFF,inversediscreteFouriertransform)的自相似通信量生成算法--FGN-IDFT算法,并通过仿真实验和比较分析的方法对该算法的精度和计算复杂度进行了大量的实验和分析。研究结果表明,利用FGN-IDFT算法生成的自相似通信量的精度和速度都令人满意,为实际网络模拟的进一步深入研究提供了基础。     

On the teletraffic capacity of CDMA cellular networks

The aim of this paper is to contribute to the understanding of the teletraffic behavior of code-division multiple-access (CDMA) cellular networks. In particular, we examine a technique to assess the reverse link traffic capacity and its sensitivity to various propagation and system parameters. We begin by discussing methods of characterizing interference from other users in the network. These methods are extremely important in the development of the traffic models. We begin with a review of several existing approaches to the problem of handling other-cell interference before presenting a novel characterization of the interference in the form of an analytic expression for the interference distribution function in the deterministic propagation environment. We then look at extending the capacity analyses that assume a fixed and equal number of users in every cell to handle the random nature of call arrivals and departures. The simplest way to do this is by modeling each cell of the network as an independent M/G/x∞ queue. This allows us to replace the deterministic number of users in each cell by an independent Poisson random variable for each cell. The resulting compound Poisson sums have some very nice properties that allow us to calculate an outage probability by analyzing a single random sum. This leads to a very efficient technique for assessing the reverse link traffic capacity of CDMA cellular networks     

The teletraffic analysis of the multi-server loss model with renewal distributions

This paper presents a loss model in which a general renewal arrival stream is served by any number of general renewal servers, i.e., theGI/GI/s/s model. Using linear algebraic queueing theory (LAQT), we provide the exact steady-state solution of the number of customers in theGI/GI/s/s model at general, arrival, and departure times. We show that the steady-state solution at arrival times can be used to approximate those at general times and that the third moment of the arrival process significantly affects this approximation. Finally, we show that a conjectured inequality does not hold.This work was performed while at the University of Missouri-Kansas City.     

Increasing the efficiency of roulette simulation of teletraffic

A simple modification of the roulette method of teletraffic simulation is presented. At low traffic levels it may result in a reduction, by a factor of ten or more, of the computer time required to simulate a specified number of calls.     

Adaptive algorithm for variable teletraffic demand in highway microcells

An adaptive algorithm is presented which ensures that the probability of a mobile radio call in progress being forced to terminate during handover in highway microcells is always small, even in the presence of high new call request rates.<>     

A teletraffic model for the Physical Downlink Control Channel in LTE

Recent advances in mobile handsets have led to new trends in mobile broadband data consumption, with a huge increase of signaling traffic generated by always-connected devices. Thus, a proper planning of control channels in mobile networks is necessary to avoid network capacity problems and provide an appropriate quality of service to the end user. A key issue in network planning is the availability of a complete and accurate system model. In this paper, an analytical performance model for the Long Term Evolution (LTE) Physical Downlink Control Channel (PDCCH) is constructed based on queuing theory. Unlike previous works, the proposed model considers important network features, such as link adaptation, and can be tuned with available network performance statistics. Model assessment is carried out by comparing performance estimates with request-level simulations and real performance measurements taken from a live LTE network. Results show that the proposed model can predict the PDCCH load distribution in a live network accurately.     

Impact of transmission impairments on the teletraffic performanceof wavelength-routed optical networks

In a wavelength-routed optical network, a transmitted signal remains in the optical domain over the entire route (lightpath) assigned to it between its source and destination nodes. The optical signal may have to traverse a number of crossconnect switches (XCSs), fiber segments, and optical amplifiers, e.g., erbium-doped fiber amplifiers (EDFAs). Thus, while propagating through the network, the signal may degrade in quality as it encounters crosstalk at the XCSs and also picks up amplified spontaneous emission (ASE) noise at the EDFAs. Since these impairments continue to degrade the signal quality as it progresses toward its destination, the received bit error rate (BER) at the destination node might become unacceptably high. Previous work on the lightpath routing and wavelength assignment (RWA) problem assumed an ideal physical layer and ignored these transmission impairments. The main contribution of our work is to incorporate the role of the physical layer in setting up lightpaths by employing appropriate models of multiwavelength optical devices (XCSs and EDFAs) such that the BER of a candidate lightpath can be computed, in advance, to determine if this lightpath should be used for the call. Features from existing RWA algorithms are integrated with our on-line BER calculation mechanism. Our simulation studies indicate that employing BER-based call-admission algorithms has a significant impact on the performance of realistic networks     

Worst-case fraction of CBR teletraffic unpunctual due tostatistical multiplexing

This paper quantitatively analyzes the queueing delay of the constant-bit-rate (CBR) traffic in a multiplexer, where the CBR traffic is mixed with the traffic of another session (interfering traffic) that has throughput and burstiness constraints. This paper focuses as a quality-of-service (QoS) measure on the fraction of the CBR traffic that fails to meet a certain delay requirement. Results include the worst-case QoS of CBR traffic as a function of the throughput and burstiness parameters imposed on the interfering traffic. Results of this paper can be applied to traffic management and call processing of asynchronous transfer mode (ATM) networks     

The role of computer modeling and simulation in electric and hybrid vehicle research and development

Computer modeling and simulation is widely used in support of electric and hybrid vehicle research and development. Many modeling-assisted studies and assessments, involving candidate technology comparisons, have been performed to provide information for management planning and research decisions. Modeling has also been extensively used in engineering activities including preliminary and final design optimization. A wide range of programs has been developed including small ones for use on hand-held programmable calculators and large programs involving more than 11 000 lines. Many programs exist in the public domain, and two major programs are available on commercial time-sharing systems.     

A novel mathematical teletraffic method to evaluate the interoperation of different standards with NOMA systems using order statistics

Basically, nonorthogonal multiple access (NOMA) allows controllable interferences by nonorthogonal resource allocation with a tolerable increase in receiver complexity, using successive interference cancellation (SIC). In this paper, authors show a novel mathematical model of teletraffic for users accessing, simultaneously, to Wi‐Fi and LTE services by using NOMA, calculating the birth–death process by order statistics. This methodology has not been previously used. The mathematical model is represented by a two‐dimensional Markovian process where the users can born or die in one system or another, independently, and results are validated through simulations. The outcomes demonstrate an increment of the sum‐rate gain for a system where users are ordered in the power domain using order statistics, according to the signal interference plus noise ratio (SINR), compared to a system where these statistics are not employed. By using the proposed mathematical model, the sum‐rate gain increases around 15%, and it is also demonstrated that this algorithm foresees a steady behavior of the sum rate, even when the number of channels is augmented, contrary when no order statistics are employed, in which the sum rate decreases considerably. On the other hand, the blocking probability is also demonstrated based on the chance of moving from one technology to another.     

A new approach to the modeling of converters for SPICE simulation

An approach to the modeling of DC-DC converters for SPICE simulation is developed in which the average current in the energy-storage inductor is first simulated in a SPICE subcircuit for both the continuous and discontinuous modes of operation. The inductor current is then weighted and redistributed to related branches of the circuit to simulate the average input and output currents of the converter. Based on this technique, various converter models, including that of the Cuk converter with coupled inductors, which are valid for both continuous and discontinuous modes of operation, are developed     

A teletraffic performance study of mobile LEO-Satellite cellular networks with gamma distributed call duration

In this paper, the authors develop an analytical model to study the performance of a mobile low earth orbiting (LEO) satellite cellular network. The model assumes that the call duration has a gamma distribution and considers the effect of system parameters such as the number of channels per cell, the number of channels reserved for the handoff, and the cell residence time, on the teletraffic performance of the system. The quality of service (QoS) measures studied in this paper include new call blocking probability, handoff failure probability, premature call-termination probability (CTP), and call dropping probability (CDP). Based on the causal central limit theorem, the authors use a two-parameter gamma distribution to approximate the distribution of the sum of the residence times in the cells. The analytical model presented in this paper may be used with any call-holding-time distribution. The analytical results are validated by a computer simulation.     

A new wire node for modeling thin wires in electromagnetic fieldproblems solved by transmission line modeling

A three-dimensional wire node for the numerical solution of electromagnetic field problems by transmission line modeling is discussed. The wire node can represent thin wires in a coarse mesh, thus substantially increasing computational efficiency. The scattering matrix for the node is given, together with a simulation result and comparisons with another method     

Inversion charge modeling in n-type and p-type Double-Gate MOSFETs including quantum effects: The role of crystallographic orientation

We have developed an advanced inversion charge model for both n-type and p-type symmetrical Double-Gate MOSFETs where quantum mechanical effects (QMEs) have been included. By doing so, the role of different crystallographic orientations was successfully taken into account. Self-consistent Poisson and Schrödinger simulators were used to check the accuracy of the model presented. As a starting point, a classical inversion charge centroid model was considered. Afterwards, an inversion charge model was developed including QMEs by means of a corrected oxide capacitance. The validity of the model was checked for the three common wafer orientations (1 0 0), (1 1 0) and (1 1 1) and for devices with different silicon layer (t_Si) and oxide (t_ox) thicknesses. As it will be shown, the model reproduces correctly the simulation data both in the subthreshold and in the strong inversion operation regime.