Yuliya V. Gaidamaka

Simulation Of Overload Control In SIP Server Networks.

In this study, we investigated a signalling load control mechanism for SIP server networks and developed a corresponding queuing model. The so-called hop-by-hop overload control, known from recent IETF drafts and RFCs, was considered and a similar buffer overload control scheme which was developed for the SS7 signalling link in ITU-T Recommendation Q.704, was proposed. The mechanism is based on hysteretic load control with thresholds for reducing potential oscillations between the control-on and control-off states under certain loading conditions. Adjustment of three types of thresholds – the overload onset threshold, the overload abatement threshold, and the overload discard threshold – makes possible the regulation of signalling traffic to meet blocking requirements. In this study, we built and analyzed the M |M |1 queue with bi-level hysteretic input load control. A numerical example illustrating the control mechanism that minimizes the return time from overloading states satisfying the throttling and mean control cycle time constraints is also presented.

Analysis of an M|G|1|R queue with batch arrivals and two hysteretic overload control policies

Abstract Hysteretic control of arrivals is one of the most easy-to-implement and effective solutions of overload problems occurring in SIP-servers. A mathematical model of an SIP server based on the queueing system M[X]|G|1(L,H)|(H,R) with batch arrivals and two hysteretic loops is being analyzed. This paper proposes two analytical methods for studying performance characteristics related to the number of customers in the system. Two control policies defined by instants when it is decided to change the system’s mode are considered. The expression for an important performance characteristic of each policy (the mean time between changes in the system mode) is presented. Numerical examples that allow comparison of the efficiency of both policies are given

Analytical Modelling And Simulation For Performance Evaluation Of SIP Server With Hysteretic Overload Control.

Major standards organizations, ITU, ETSI, and 3GPP have all adopted SIP as a basic signalling protocol for NGN. The current SIP overload control mechanism is unable to prevent congestion collapse and may spread the overload condition throughout the network. In this paper, we investigate one of the implementations of loss based overload control scheme developed by IETF work group which uses hysteretic load control technique on the server side for preventing its overloading. Two different approaches to calculate performance measure of SIP server are introduced. We follow an analytical modelling approach to construct and analyse SIP server model in the form of queuing system with finite buffer occupancy and two-level hysteretic overload control. The formulas for stationary probabilities and the mean return time in the set of normal states were obtained. Simulation is the other approach which allows to eliminate disadvantages of analytical modelling. At present, there is no simulator for modelling of SIP servers in overload conditions with an application of overload control mechanisms which are currently under development by IETF. Approaches to its programming implementations which reflects the protocols and functions that are fully or partially built into the original SIP systems are proposed in the paper.

Analytical performance estimation of network-assisted D2D communications in urban scenarios with rectangular cells

The aggressive spatial reuse of radio resources is considered today as one of the most promising avenues to achieve significant cellular capacity improvements in future fifth-generation networks. Accordingly, device-to-device (D2D) communications are an emerging paradigm that promises to offer these much expected gains without the need for additional investments into the network infrastructure. However, before this attractive technology can be deployed ubiquitously, the research community has to fully understand the extent of its potential performance benefits across typical scenarios of interest. In this work, we consider one such use case of rectangular cells (common for offices, shopping malls, dormitories, etc.) and develop the corresponding analytical methodology for D2D performance evaluation. As our target metric, we employ the signal-to-interference (SIR) ratio experienced by a D2D user. To this end, we propose two relatively simple approximations for SIR distribution and hence capture the related parameters, including user throughput. Further, we carefully investigate the most interesting numerical results by making important conclusions on the envisioned operation of our chosen scenario. In particular, we demonstrate that under certain conditions, the SIR behaviour is insensitive to the dimensions of cells, while different propagation exponents ‘scale’ its density function thus allowing to simplify the characterisation of SIR in a wide range of input parameters. Copyright

Discrete Markov chain model for analyzing probability measures of P2P streaming network

In this paper, we present a model of the data exchange process between users in P2P live streaming network with buffering mechanism - buffer occupancy model. The model is developed in terms of discrete Markov chain. We study the probability measures of the model - buffer position occupancy probability and probability of playback continuity. The model is very tractable and compacted formulas were obtained. While considering user churn in the model we examine how user departure affects buffer occupancy and playback continuity. For our numerical experiment we develop a simulation tool for the considered model.

Random Triangle: A Baseline Model for Interference Analysis in Heterogeneous Networks

In emerging heterogeneous networks (HetNets), a wide range of the underlying performance evaluation problems is related to wireless interference characterization and can be reduced to investigating the distribution of a side length in a random triangle. In this paper, we address the task of calculating the side-length distribution in such a triangle determined by the known distributions of its two other sides and the distribution of the angle between them. No restrictions on the distributions of input random variables (RVs) are imposed except for their statistical independence. Our solution delivers a crucial building block for interference analysis in multitier and multiradio HetNets, including mobile device-to-device communication as one of the most extreme interference-limited cases.

Utility function maximization problems for two cross-layer optimization algorithms in OFDM wireless networks

One of the main problems in wireless networks is optimization of radio resources allocation in down-link channel. Different traffic types transmitted over the network suggest a dynamic resource allocation in order to provide a better quality of service (QoS). There are radio resource management modules, called schedulers, which are engaged in resource planning and access priority assignment depending on the types of traffic with the specified requirements for QoS. Schedulers are developed based on algorithms derived from solving various radio resources optimization problems. Cross-layer optimization problems such as the problem of minimizing the transmission power or the problem of maximizing the transmission rate [1], in fact involve the optimization of a utility function, that describe a certain level of user satisfaction for a particular resources allocation scheme under certain restrictions. In this paper we study two cross-layer optimization algorithms that are intended to maximize the utility function under different conditions - dynamic subcarrier assignment (DSA) algorithm and adaptive power allocation (APA) algorithm.

An Analytical Approach to SINR Estimation in Adjacent Rectangular Cells

Signal-to-interference-plus-noise ratio (SINR) experienced by a mobile user is the key metric determining the throughput it receives over a certain wireless technology of interest. In this paper, we propose an analytical model for SINR estimation in rectangular-shaped cells for cases when noise can be considered negligible. This scenario is common for offices, shopping malls, dormitories, etc. We address uplink and downlink communications showing that in both cases the integral expressions can be derived. Various extensions to the proposed model are discussed. We also elaborate on the numerical results highlighting the important dependencies for the chosen scenario.

Time-Dependent SIR Modeling For D2D Communications In Indoor Deployments.

Device-to-device (D2D) communications is expected to become an integral part of the future 5G cellular systems. The connectivity performance of D2D sessions is heavily affected by the dynamic changes in the signal-to-interference ratio (SIR) caused by random movement of communicating pairs over a certain bounded area of interest. In this paper, taking into account the recent findings on the movement of users over a landscape, we characterize the probability density function (pdf) of SIR under stochastic motion of communicating D2D pairs on planar fractals. We demonstarte that the pdf of SIR depends on the fractal dimension and the spatial density of trajectories. The proposed model can be further used to investigate timedependent user-centric performance metrics including the link data rate and the outage time.

Analysis of Business Process Execution Time with Queueing Theory Models

In the paper an approach to the analysis of business process efficiency is proposed. A method for the estimation of a business process execution time as an important performance measure of business processes efficiency is developed. It represents a combination of queuing networks modelling and simplex algorithm of linear programming. The method allows the calculating of the minimum business processes execution time. A method of optimizing activity of the telecommunication company at a predetermined threshold for the business processes execution time is given. The developed technique was illustrated with an end-to-end business process flow “Request-to-Answer” with initial data close to reality.