VBR Video Sources Research Articles

Performance of a new bus assignment algorithm for an ATM switch fabric

The measurement of the quality of service in ATM* networks involves the activation of the ATM layer management OAM functions. Once an ATM connection is set up, in-service performance monitoring based on OAM cells can be used to measure and estimate the ATM layer QoS parameters. In-service measurement of ATM layer QoS parameters such as cell delay variation, cell transfer delay, cell loss ratio, etc., is necessary to verify on one hand, if the network is meeting the requested QoS and on the other hand, if the users are receiving their promised QoS. Congestion conditions in ATM switches may cause gradual deteriorations in the quality of virtual paths or virtual channel connections in an ATM network. QoS measurement using OAM cells can accurately measure the overall quality of monitored ATM layer QoS parameters in order to detect such deteriorations before the service quality has dropped bellow an acceptable level. Several factors such as network load, congestion, bottlenecks, and incremenTS in network load may affect the cell delay variation of video transmissions in an ATM network. In this work, several ATM layer QoS parameters have been measured on a VBR video source using OAM cells. The simulation resulTS obtained show that with low network loads, the contribution of each individual ATM switch to the local and to the end-to-end CDV is not significant. In the presence of a bottleneck switch, the CDV presented by this switch becomes the dominant one at both local and end-to-end sides. When the network load is between 0.5 and 0.6, small incremenTS in network load do not alter the buffer performance of the non-congested ATM switches, and low values of CDV can be obtained. In contrast, it was found that there is a critical load between 0.65 and 0.7 where small incremenTS in network load may force the CDV to grow abruptly.

Asynchronous measurement of CDV in ATM networks using OAM cells

The synchronisation between source and destination clocks at network nodes to a common reference time of day is important in order to achieve accurate measurements of cells delays in ATM networks. Otherwise, direct measurement of the cell transfer delay and cell delay variation using time-stamped OAM cells would be inaccurate. In this work, a method for the accurate measurement of cell delay variation using OAM cells, which does not rely on synchronised clocks at the measurement points is presented. This is achieved by assuming that each ATM switch has the capability to process and to modify the information contained in the OAM cells. The system presented here was modelled by means of a block-oriented network simulator (BONeS), which is a graphically-oriented, general-purpose simulation language for modelling and simulating communications networks, including ATM networks. The measurements of the cell delay variation were carried out on a VBR video source generated by a real MPEG-2 encoder with a fixed quantizer step size. The simulation results obtained show that measurements of the cumulative cell delay variation carried out without synchronised clocks at the measurement points were very closed to those obtained using synchronised clocks at the measurement points.

Predictive and measurement-based dynamic resource management and QoS control for videos

In this paper, we propose a new dynamic resource allocation and call admission control method for the VBR video sources to meet the user's quality of service requirements and at the same time to achieve an efficient resource management in networks. Without any prior knowledge of the user's traffic statistics, the proposed mechanism dynamically adjusts the necessary bandwidth by the networks based on the provided quality of service satisfaction degree of each connection in respect to the user's requirements in terms of loss ratio and average delay. Using traffic prediction and simple QoS measurements, the next required bandwidth for each video connection is computed. To avoid quality decreasing by new incoming calls, we present a call admission control based on the provided QoS for existing connections. Simulation results show that our proposed dynamic method is able to provide the desired level of quality of service and high network utilization.

An application of Markovian arrival process (MAP) to modeling superposed ATM cell streams

First, we propose a new modeling method for superposed ATM traffic by the MMPP(2), which is a special case of the MAP(2). In this new method, we measure the mean and autocorrelation of cell interarrival times, and the histogram of the number of arrivals during measurement windows of fixed size. The MMPP(2) has interarrival times with a second-order hyper-exponential distribution with coefficient of variation c/sub /spl nu// > 1. However, superposed traffic is often observed to have c/sub /spl nu// < 1. To cover this situation, we extend the MMPP(2) to a MAP(3) by adding a new state with inter-state transition accompanied by an arrival. For the MAP(3) model, we take into account the second moment of the interarrival times. From numerical examples, we observe that both the proposed MMPP(2) and MAP(3) yields very good estimation of the cell loss ratio (CLR) for usual superpositions of voice and/or VBR video sources. However, when we have superpositions from CBR video sources together with other VBR sources, c/sub /spl nu//. is much less than 1, and the MAP(3) outperform the MMPP(2), as expected. The proposed MAP(3) well characterizes the cell scale component as well as the burst scale component of superposed traffic streams.

VBR Video Source Characterization and a Practical Hierarchical Model

There are many ways to build up traffic models for VBR video sources. A frequently applied methodology is to use mathematical analysis based on realistic assumptions to set up a source model that generates traffic according to a stochastic process. In this case, the critical issue is the validation of the synthetic trace by comparing statistics to results obtained from measurements on the real source. In this paper, we choose a different and more practical approach to model the behavior of the real traffic source. Our model building philosophy is that we analyze and understand what happens with the video information on its way from the ingress to the multimedia terminal to the egress of the network card. Throughout this journey the information is processed by several mechanisms and we build an empirical model step by step based on our measurement-based observations. Besides understanding the traffic generation procedure, statistical analysis of VBR traffic traces captured from a number of video sequences was also carried out in several scenarios. Using the knowledge of encoding, encapsulation and scheduling processes and results of the trace analysis, a hierarchical source model is set up for modeling the multimedia terminal. Thereby our model imitates the generation of video frames and the inner working of each level of protocol hierarchy and tries to reproduce the complex behavior of the real source. We use the leaky bucket analysis for verification of the model in order to capture directly the behavior of the traffic in a queue.

Dynamic bandwidth allocation scheme for multiple real-time VBR videos over ATM networks

This paper considers VBR transmission of multiple real?time videos over ATM networks. Multiple real?time VBR video sources are multiplexed into an ATM switch to transmit cells into the network. Given the ATM switch capacity, the problem is to dynamically allocate the required channel bandwidth for each video source such that the encoder buffer occupancy is maintained at a target level. To solve the problem, we present a mathematical formulation and propose an algorithm for the bandwidth allocation. To allocate a suitable bandwidth at a given control period, QoS demand levels and traffic characteristics of the video sources are considered. The performance of the proposed scheme is examined in terms of the number of encoder rate controls required and the gap between the target and the current buffer occupancy at each control period. Numerical results are analyzed for different QoS environments as well as different levels of target buffer, ATM switch capacity, buffer size and leaky bucket token rate.

Semi-Markov model for a generalized VBR video in ATM networks

A semi-Markov model describing the performance of an ATM multiplexer with VBR video sources as inputs is presented. The considered system consists of the bit-streams generated by a collection of these sources. The streams which are first separately packetized into fixed size cells, and then, through a statistical multiplexer, join a common queue (assumed to be infinite) where they are served on a FIFO basis by a constant capacity channel. The model to be used is based on the assumption that the video sources operate in two bit-rate modes with unequal average holding times. Each video source is decomposed into an aggregate of two types of ON/OFF mini-sources. Multiplexing a number of such sources leads to a semi-Markov process, which is defined and solved using a phase process with as states the number of active mini-sources of each type. By relating an embedded Markov chain to this phase process, a solution to the resulting queueing system is presented, and the queue length distribution is derived using matrix---geometric techniques. Lastly, results are presented showing that the system performance depends not only on the ratio of the average holding times in the two modes, but also on their magnitudes.

A simulation based approach for network resources dimensioning in video delivery systems

The availability of high-performance networking technologies and processing power allows creation of new multimedia services and applications in broadband integrated services networks. Such new services will be successful only if delivered to end-users at low cost. At present, for wide-area distributed systems, communication has a relevant impact on the overall costs. As a consequence, adequate methodologies for an efficient dimensioning of the network resources need to be devised. Simulation techniques represent a powerful instrument for the analysis and evaluation of real systems. This paper, moving from the definition of mathematical models for VBR video sources, presents the application of a simulation approach to verify the compatibility of the communication load related to a set of video streams with the data transport capability of an existing network architecture for the delivery of video streams, in the case of CBR communication links.

Queue Size Distribution of an ATM Switch with VBR Video Traffic

Many analytical tools have been devised to analyze CBR video coders, however only few have been applied to the VBR case. In this paper, we present a semi-Markov process model for approximating the stochastic equilibrium queue length distribution for VBR video sources multiplexed onto a constant capacity ATM channel. The sources are assumed to have two rates, and generate cells that pass through pre-buffers before joining a common queue on a FIFO basis. The model is based on a state process defined by the average rate of change of the queue length as a function of the number of active mini-sources of each type, and is solved using matrix-geometric techniques. An Access Control mechanism uses these results inside its policing function to control access to the network at call setup. Numerical results are obtained for various conditions, and compared to the ones obtained from simulation and fluid-flow models, and good agreement was achieved.

An effective model for VBR video with application to an ATM multiplexer

The effective design and engineering of communication networks require accurate mathematical models that should capture the important statistical properties of traffic sources. The ATM Forum has specified some QoS requirements for video traffic, which are essential for the effective management and operation of ATM networks. In this paper, a model for VBR video sources using a modified first-order autoregressive model is presented. Two levels of states with arbitrary average duration are used to represent the source bit-rate. The corresponding ratio of the statistical duration averages in the two levels is used as a new parameter to quantify the activity behaviour of the pertinent sources. A derivation for the resulting model statistical equations is presented and matched to some experimental data. Then, the obtained matched parameters are plugged into the simulation model. The major results are presented for various parameter values, along with an assessment of their effects on the performance of an ATM multiplexer.

Three-level traffic shaper and its application to source clock frequency recovery for VBR video services in ATM networks

Studies the traffic shaping issues for VBR video services in ATM networks with stress put on the source clock frequency recovery aspect. The authors propose a three-level traffic shaper (TLTS) which is able to limit the minimum as well as the maximum cell rate of input VBR traffic. For a VBR video source modeled after a two-state Markov modulated Poisson process, they determine, as performance measures, the cell loss probability, the underflow probability, and the maximum delay that a cell can experience in the proposed TLTS. Then they apply the TLTS for source clock frequency recovery in VBR video services. In extending the existing CBR-based synchronous residual time stamp (SRTS) method for VBR video services, it is necessary to restrict the minimum, as well as the maximum, number of cells generated in a fixed period of time to ensure the transmission of timing information, and the proposed TLTS is tailored to meet this necessity by adopting an optimal dimensioning procedure based on the genetic algorithm (GA). Finally the authors provide some numerical examples to demonstrate the optimal dimensioning procedure of TLTS and the related performances of statistical multiplexing and source clock frequency recovery. >