The dramatically increased bandwidths and processing capabilities of future high-speed networks make possible many distributed real-time applications, such as sensor-based applications and multimedia services. Since these applications will have traffic characteristics and performance requirements that differ dramatically from those of current data-oriented applications, new communication network architectures and protocols will be required. In this paper we discuss the performance requirements and traffic characteristics of various real-time applications, survey recent developments in the areas of network architecture and protocols for supporting real-time services, and develop frameworks in which these, and future, research efforts can be considered.

Compressed digital video is one of the most important traffic types in future integrated services networks. However, a network service that supports delay-sensitive video imposes many problems since compressed video sources are variable bit rate (VBR) with a high degree of burstiness. In this paper, we consider a network service that can provide deterministic guarantees on the minimum throughput and the maximum delay of VBR video traffic. A common belief is that due to the burstiness of VBR traffic, such a service will not be efficient and will necessarily result in low network utilization. We investigate the fundamental limits and tradeoffs in providing deterministic performance guarantees to video and use a set of 10 to 90 minute long MPEG-compressed video traces for evaluation. Contrary to conventional wisdom, we are able to show that, in many cases, a deterministic service can be provided to video traffic while maintaining a reasonable level of network utilization. We first conside...

For the performance analysis of ATM networks carrying Variable Bit Rate (VBR) MPEG video sequences there is a need for appropriate video traffic models. In this paper, we discuss Markov chain models for this specific type of traffic with respect to several statistical properties and their ability to predict cell losses at buffers of ATM multiplexers. We intentionally selected a simple model class to check for its appropriateness to model a complex traffic type. The results of this paper show that Markov chain models can be used efficiently for MPEG video traffic under the following conditions. The Group of Pictures (GOP) generation process should be modeled rather than the frame process. If the performance measures depend on the correlation properties of the video traffic the scene process should also be considered in the course of the model development. 1 Introduction In B-ISDNs on the basis of the ATM, a major part of the traffic will be generated by multimedia sources like teleco...

Modern telecommunications networks are being designed to accomodate a heterogenous mix of traffic classes ranging from traditional telephone calls to video and data services. Thus, traffic models are of crucial importance to the engineering and performance analysis of telecommunications system, notably congestion and overload controls and capacity estimation. This chapter surveys teletraffic models, addressing both theoretical and computational aspects. It first surveys the main classes of teletraffic models commonly used in teletraffic modeling, and then proceeds to survey traffic methods for computing statistics relevant to the engineering a teletraffic network. 1 INTRODUCTION Traffic is the driving force of telecommunications systems, representing customers making phone calls, transferring data files and other electronic information, or more recently, transmitting compressed video frames to a display device. The most common modeling context is queueing; traffic is offered to a qu...

: Variable bit rate (VBR) video is expected to be a major source of traffic for the Broadband Integrated Services Digital Network (B-ISDN). To dimension the network, there is a need to predict the network performance. Traffic models are often used as an aid in this process, and many have been proposed as suitable for the modeling of VBR video sources. However, further work is required in the area of verifying the accuracy of models, and little comparison between models is available. In this paper, several of these models are presented and their properties discussed, including their ability to predict accurately different aspects of network performance, with an emphasis on cell loss statistics. Finally, some time is spent reviewing a number of open questions in modeling video streams and their superposition, and the analysis of queueing systems with this kind of input. 1 Introduction Variable bit rate (VBR) video is expected to be a major source of traffic for the Broadband Integrate...

We consider a finite-capacity ATM multiplexer in discrete-time domain. The input traffic is the superposition of the traffic from different classes. Each class is formed by a number of periodic input sources (e.g. voice or shaped VBR sources) which are of the same periodicity. We investigate the autocorrelation function and the power density spectrum to show traffic dependencies in the multiplexer output process. We derive an exact solution for the autocorrelation function and the power density spectrum of the multiplexer output process when only one traffic class is considered. We show that the algorithm for the finite-capacitymultiplexer can also be applied for the case of an infinitecapacity multiplexer when the number of buffer places is set to a sufficiently large but finite value. By numerical examples it is shown that considering ON/OFF input sources instead of periodic input sources lead only to slightchanges in the autocorrelation function and that the main characteristics of it are preserved. We propose an approximate analysis for more than one input traffic class which uses the exact results for one traffic class. The numerical results are compared to simulation results and are in good agreement. It turns out that the power density spectrum of the multiplexer output process can be used to determine how many sources of which periodicity deliver cells to the multiplexer input. Since the measurement of the power density spectrum can be performed by standard signal processing equipment the power density spectrum can be used for several control functions (e.g. routing, admission control) inside an ATM network.

Compression of digital video is the only viable means to transport real-time full-motion video over BISDN/ATM networks. Traffic streams generated by video compressors exhibit complicated patterns which vary from one compression scheme to another. In this paper we investigate the traffic characteristics of video streams which are compressed based on the MPEG standard. Our study is based on 23 minutes of video obtained from an entertainment movie. A particular significance of our data is that it contains all types of coded frames, namely: Intra-coded (I), Prediction (P), and Bidirectional (B) MPEG frames. We describe the statistical behavior of the VBR stream using histograms and autocorrelation functions. A procedure is developed to determine the instants of a scene change based on the changes in the size of successive I frames. It is found that the length of a scene can be modeled by a geometric distribution. A model for an MPEG traffic source is developed in which frames are generated...

In this paper an accurate and treatable Markov-based model for MPEG video traffic is proposed. Before reaching a definition of the model, a large number of MPEG video sequences are analyzed and their statistical characteristics are highlighted. Besides the well-known autocorrelation function, testifying the pseudo-periodicity of the sequence in the short term, and the Gamma-shaped probability density function, the correlation between different frames belonging to the same Group of Pictures (GOP) is also accurately studied. Then a structured model is proposed. Thanks to its two-level structure, it is able to capture both the inter-GOP and the intra-GOP correlation. In order to obtain the first level of the model, the well-known inverse eigenvalue problem is solved in the discrete-time domain. Finally, the model is used to evaluate the loss probability in an ATM multiplexer loaded by an MPEG video source and an aggregate of external traffic. The accuracy of the model is evaluated by comparing the analytically obtained loss probability with the loss probability calculated by simulating the system using real traffic sequences as driven traces.

Measurement-based traffic characterization has come to acquire a great deal of importance in high-speed networks. In this paper, we segregate the traffic behaviour into the macrodynamics and microdynamics depending on the time scales at which the process is observed. We examine the validity of the Markovian assumption which is commonly made for modeling the macrodynamics of correlated traffic in network analysis. A fundamental issue in traffic modeling is whether the Markovian assumption has any significance on the queueing solutions. Our study compares the queueing solutions obtained using traffic models with very different underlying structure viz. Markovian vs non-Markovian which are identical only in their second-order and steady-state statistics. Our study suggests that higher-order traffic statistics are generally unimportant to queueing solutions. In essence, for a certain class of stationary stochastic processes, the Markovian assumption can be made in traffic modeling to simpl...

The paper contributes results on the modeling of videoconferencing traffic over IP networks. The study is based on extensive data, gathered by tracing the actual packet exchange during a comprehensive set of realistic teleconferencing sessions over an asymmetric platform, in which commercial H.261-compliant terminal clients were communicating through a Multipoint Control Unit (MCU) at ‘continuous presence ’ mode. Analysis of the data suggests that the video traffic from the client terminals can always be represented at the frame level as a stationary stochastic process with an autocorrelation function of exponentially fast decay and a marginal frame size distribution of approximately Gamma form. The video traffic from the MCU to the clients is again stationary and with exponentially decaying correlations, while the corresponding marginal frame-size PDF has the form of an appropriately weighted sum of Gamma components, the number of terms in the sum always being equal to the number of conferring terminals. The paper discusses methods for correctly matching the parameters of the modeling components to the data and for combining these components into complete traffic models that have been proposed in the literature. Keywords: Videoconference systems, video bridging, multipoint control units (MCU), H.261 video coding, IP-traffic measurements, traffic modeling 1.