Pavel O. Abaev

Queuing Model for Loss-Based Overload Control in a SIP Server Using a Hysteretic Technique

In this paper, we develop a mathematical model of a load control mechanism for SIP server signaling networks based on a hysteretic technique developed for SS7 from ITU-T Recommendation Q.704. We investigate loss-based overload control, as proposed in recent IETF documents. The queuing model takes into account three types of system state – normal load, overload, and discard. The hysteretic control is made possible by introducing two thresholds in the buffer of total size B – the overload onset threshold H and the overload abatement threshold L. We denote the mathematical model using the modified Kendall notation as an \(M|G|1|\left\langle L,H\right\rangle |B\) queue with hysteretic load control. We also develop an analytical model for the case of an M|M|1 queue and a simulation model for an M|D|1 queue. We investigate the return time from an overload state as the target performance measure of overload control in a SIP server, and provide numerical examples in order to examine the difference between the M|M|1 and M|D|1 systems.

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.

Modeling of Hysteretic Signaling Load Control in Next Generation Networks

In this paper we investigate traffic load control mechanisms for controlling congestion in signaling networks based on three types of thresholds. The goal of the paper is to analyze congestion controlling mechanisms and develop corresponding queuing models of SIP servers. The study is based on hysteretic congestion control, which has been developed for Signaling System 7 (SS7). Models for describing the hysteretic control are developed. The current state and problems of basic overload control mechanism proposed by Internet Engineering Task Force (IETF) for SIP signaling networks are investigated. Approaches to building mathematical models of SIP servers in the form of a queuing system with hysteretic control are proposed.

On analytical model for optimal SIP server hop-by-hop overload control

In this paper, we present analytical results of the analysis of the queueing system that models signalling hop-by-hop load control mechanism for SIP server. The so-called hop-by-hop overload control, known from recent IETF drafts and RFCs, is based on hysteretic load control with two thresholds for reducing potential oscillations between the control-on and control-off states under certain loading conditions. Adjustment of thresholds values makes possible the load control of signalling traffic and therefore meeting blocking requirements. New approach that allows fast computation of joint stationary probability distribution of finite M2|M|1|R queue with bi-level hysteretic input load control is proposed. Illustrative numerical example is given to demonstrate some optimization issues.

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.

Analysis of Queueing System with Constant Service Time for SIP Server Hop-by-Hop Overload Control

Consideration is given to the analysis of queueing system M 2|D|1|R with bi-level hysteretic input load control that can model signalling hop-by-hop overload control mechanism for SIP servers described in RFC 6357. Bi-level hysteretic input load control implies that system may be in three states (normal, overloaded, blocking), depending on the total number of customers present in it, and upon each state change input flow rate is adjusted. New approach that allows fast computation of joint stationary probability distribution is proposed, expressions for important performance characteristics are given.

Queuing Model for SIP Server Hysteretic Overload Control with Bursty Traffic

In this paper, we develop a mathematical model of a load control mechanism for SIP server signaling networks based on a hysteretic technique. We investigate loss-based overload control, as proposed in recent IETF documents. The queuing model takes into account three types of system state – normal load, overload, and discard. The hysteretic control is made possible by introducing two thresholds, L and H, in the buffer of total size R. We denote the mathematical model using the modified Kendall notation as an \(MMPP|M|1|\left\langle L,H\right\rangle |R\) queue with hysteretic load control and bursty input flow. Algorithms for computation the key performance parameters of the system were obtained. 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.

On Mean Return Time in Queueing System with Constant Service Time and Bi-level Hysteric Policy

Single server queueing system with two Poisson input flows of rate λ 1 and λ 2, finite queue of size R − 1 < ∞ and bi-level hysteretic policy is considered. Customers of λ 1 flow are served with relative priority. Customers of both flows are served with the same constant service time. Bi-level hysteretic policy implies that system may be in three states (normal, overload, blocking), depending on the total number of customers present in it. New method for calculation of mean return time to normal operation state is proposed.

SIR Analysis In Square-Shaped Indoor Premises.

The increased wireless network densification has resulted in availability of wireless access points (AP) in almost each and every indoor location (room, office, etc.). To provide complete in-building coverage very often an AP is deployed per room. In this paper we analyze signal-to-interference (SIR) ratio for wireless systems operating in neighboring rooms separated by walls of different materials by explicitly taking into account the propagation and wall penetration losses. Both AP and direct device-to-device (D2D) configurations are addressed. Our numerical results indicate that the performance of such system is characterized by both the loss exponent describing the propagation environment of interest and wall materials. We provide the numerical results for typical wall widths/materials and analyze them in detail. INTRODUCTION The predicted increase in the user traffic demands places extreme requirements on the future evaluation of mobile systems, often referred to as fifth generation (5G) networks [1], [2]. In addition to physical layer improvements including advanced modulation and coding and MIMO techniques, over the last decade researchers investigated a number of network solutions providing decisive performance improvements including the use of small (micro/pico/femto) cells [3], clientrelays [4], direct in-band and out-of-band device-to-device communications [5]. All these concepts target aggressive spatial reuse of frequencies promising substantial area capacity gains. With the adoption of novel mechanism the user devices are expected to take a more active part in 5G systems and, in some cases, even take on the role of the network infrastructure in providing wireless connectivity such as offering D2D-based data relaying, proximity services, etc. This shift from the classic cellular model is dictated by the progress in communications technologies: the user devices are augmenting their capabilities, whereas the base stations (BSs) are becoming smaller as a result of the ongoing network densification [6]. The networks densification, novel networking and service mechanisms as well as the trend to use multiple access technologies to serve the users, known as heterogeneous cellular system concept, altogether lead to increased randomness of the network, where the positions of servicing stations such as BSs, relays and D2D partners are random rather than deterministic. The signal-to-interference ratio (SIR) is a universal metric specifying performance of wireless systems [7]. Once SIR is known one could describe the Shannon rate of the channel and spectral efficiency of the system. In contrast to noise-limited systems, where the bit error rate (BER) decreases exponentially with signal-to-noise ratio (SNR), the heterogeneous mobile networks are interference-limited showing linear improvement of BER with respect to SIR. Thus, the increase of the emitted power does not improve the performance of these systems. Thus, the problem of finding SIR for typical network configurations is of special importance characterizing applicability and typical scenarios of modern and future wireless technologies. The SIR performance of wireless systems is often studied using the tools of stochastic geometry [8]. The basic approach is to specify the point process on the plane modeling positions of the stations and then derive the interference at the point of interest. The last step is rather complex as we need closed-form distribution of distance to the point of interest from at least several neighboring points. For this reason typical considered models are often limited to Poisson point process on the plane for which we immediately have closed-form expressions for distributions of distances to the i-th neighbor [9]. The constantly increasing need for wireless connectivity on-the-go [10] are gradually changing the way service is provisioned in wireless networks. Nowadays, one of the trends is to deploy small wireless stations including both IEEE 802.11 or micro-LTE access points (AP) in crowded areas to benefit from increased network densification [6] and shorter propagation distances. Examples include large shopping mall, office environment, where one of few adjacent rooms is served by an AP having relatively small coverage area. In this dense environment interference between neighboring APs is inevitable and may easily lead to degraded system performance. In this paper, using the tools of stochastic geometry, we analyze performance of wireless systems operating in neighboring rooms of rectangular configuration. We consider both direct device-to-device and AP configurations assuming that Proceedings 30th European Conference on Modelling and Simulation ©ECMS Thorsten Claus, Frank Herrmann, Michael Manitz, Oliver Rose (Editors) ISBN: 978-0-9932440-2-5 / ISBN: 978-0-9932440-3-2 (CD) the systems in adjacent rooms operate at the same frequency. The analytical results are compared to simulations showing adequate agreement. Numerical results for the set of input metrics demonstrate that the system performance is dictated by the interplay between path loss exponent typical for a given environment and type of the walls used between rooms. The rest of the paper is organized as follows. First, in the next section we introduce a system model. Further, we analytically study SIR for downlink scenario. The simulation models for both downlink and D2D scenarios are introduced next. Numerical results for different sets in input variables are illustrated. Conclusions are drawn in the last section. SYSTEM MODEL In this study we focus on an indoor scenario with grid aligned rooms, see Fig. 1 that are typical for shopping malls or office buildings. In these environments rooms are often of rectangular or square shapes. Each room is assumed to be equipped with an AP deployed in the geometrical center. To take advantage of the wireless network densification trend as a solution to upgrade the degree of spatial reuse, the devices in adjacent rooms are assigned the same set of communication channels [6]. The mobile terminals (users) operating over the same channel are assumed to be uniformly distributed over the room, one per room. We concentrate on the so-called tagged user in the central room, see Fig. 1(a) and Fig. 1(b). We assume both AP and users to be equipped with omnidirectional antennas. We do not focus on a particular radio technology addressing the general case. In addition to AP scenario we also address D2D configuration, sketched in Fig. 1(c). The principal difference compared to AP case is that both transmitter and receiver are assumed to be uniformly distributed within a room. Under this assumption the configuration is symmetric, i.e., we do not have to distinguish between uplink and downlink cases. Similarly, we concentrate on D2D pair located in the central room. Focusing on SIR, as a metric of interest, for both AP and D2D configurations we calculate it for a randomly chosen receiving device, taking into account the interference from a set of neighboring rooms. Using the commonly used propagation model, we add a correction factor, accounting for the attenuation of a signal when passing through a wall

FSM Based Simulation For Performance Evaluation Of SIP Server Loss-Based Overload Control.

The rapid development of services provided on SIP networks not only define the necessity of creating new equipment and standards but also requires the development of new methods and programming software tools for modeling and analyzing the effectiveness of the overload control mechanisms in SIP-server networks. The modeling process utilizes mathematical and simulation models as well as simulators. Only simulators or simulation tools make it possible to solve problems related to the analysis and optimization of the control parameters. The most appropriate modeler is the simulators reflecting the protocols and functions, which are fully or partially built into the original system. At present, there are no simulators for modeling the work of SIP servers in overload conditions with an application of mechanisms, which are currently under development by IETF SIP Overload Control workgroup. Simulation tool that supports the main SIP RFCs such as RFC 3261 are proposed in the paper. The architecture of SIP node is developed, and numerical example is presented.