We develop a network calculus for processes whose burstiness is stochastically bounded by general decreasing functions. This calculus enables us to prove the stability of feedforward networks and obtain statistical upper bounds on interesting performance measures such as delay, at each buffer in the network. Our bounding methodology is useful for a large class of input processes, including important processes exhibiting "subexponentially bounded burstiness" such as fractional Brownian motion. Moreover, it generalizes previous approaches and provides much better bounds for common models of real-time traffic, like Markov modulated processes and other multiple time-scale processes. We expect that this new calculus will be of particular interest in the implementation of services providing statistical guarantees.

We present an experimental analysis of on-off patterns in Voice over IP (VoIP), where we study the talk-spurt/gap distribution produced by two modern silence detectors: ITU G.729 Annex B Voice Activity Detector (VAD) and NeVoT Silence Detector (SD). The results indicate that spurt/gap distributions are fairly sensitive to both the sound volume and the type of silence detectors, but all of them showed that the traditional assumption of exponential distribution does not always fit well with the audio sessions we recorded. Both the spurt and gap distributions are more "heavy-tailed" than the exponential curve. In particular, the gap distribution deviates much more strongly from the exponential model, even when "hangover" is applied.

IEEE 802.11 is a Media Access Control (MAC) protocol which has been standardized by IEEE for Wireless Local Area Networks (WLAN). The IEEE 802.11 MAC protocol offers two types of services to its users: synchronous and asynchronous. This paper thoroughly analyzes, by simulation, the asynchronous part alone, when each station feeds the MAC protocol with data traffic patterns (in the following referred to as advanced data traffic) that are very close in shape to those generated by a terminal accessing, for example, the WWW service. Although the analysis shows that the performance of the IEEE 802.11 with advanced traffic is considerably worse than with Poissonian traffic, we can conclude that IEEE 802.11 still performs satisfactorily. Furthermore, our analysis is broadened to include higher medium capacities up to 10 Mbit/sec. This part of the analysis shows that the IEEE 802.11 MAC protocol is not adequate to work at speeds planned for the upcoming ATM Wireless LAN. 1.0 Introduction The...

Abstract — In this paper we develop a simple and accurate analytical technique to determine the loss probability at an access node to an asynchronous transfer mode (ATM) network. This is an important problem from the point of view of admission control and network design. The arrival processes we analyze are the Markov-modulated Poisson process (MMPP) and the Markov-modulated fluid (MMF) process. These arrival processes have been shown to model various traffic types, such as voice, video, and still images, that are expected to be transmitted by ATM networks. Our hybrid analytical technique combines results from large buffer theories and quasi-stationary approaches to analyze the loss probability of a finite-buffer queue being fed by Markov-modulated sources such as the MMPP and MMF. Our technique is shown to be valid for both heterogeneous and homogeneous sources. We also show that capacity allocation based on the popular effective-bandwidth scheme can lead to considerable underutilization of the network and that allocating bandwidth based on our model can improve the utilization significantly. We provide numerical results for different types of traffic and validate our model via simulations. Index Terms—Admission control, bandwidth allocation, effective bandwidth, large deviations, loss probability, Markov models, MMPP, queueing analysis. I.

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...

Real-time traffic measurements on MAGNET II, an integrated network testbed based on Asynchronous Time Sharing, are reported. The quality of service is evaluated by monitoring the buffer occupancy distribution, the packet time delay distribution, the packet loss and the gap distribution of the consecutively lost packets. Our experiments show that both time delay and buffer occupancy distributions of multiplexed video sources display a marked bimodal behavior, which does not seem to depend on the buffer size. The reliance of the network designer on traffic sources that do not exhibit substantial correlations can lead to implementations with serious congestion problems. For ATS based networks with different traffic classes, the impact of a traffic class on the performance of the other classes tends to be diminished when compared with one class based ATM networks. March 23, 1995. Published in IEEE Journal on Selected Areas in Communications, April 1990 Real-Time Traffic Meas...

This paper quantitatively evaluates several alternative approaches to the scheduling of cells in a highbandwidth input-queued ATM switch. In particular, we compare the performance of three algorithms described previously: FIFO queueing, parallel iterative matching (PIM), maximum matching and two new algorithms: iterative round-robin matching with slip (SLIP) and least-recently used (LRU). For the synthetic workloads we consider, including uniform and bursty traffic, SLIP performs almost identically to the other algorithms. Cases for which PIM and SLIP perform poorly are presented, indicating that care should be taken when using these algorithms. But, we show that the implementation complexity of SLIP is an order of magnitude less than for PIM, making it feasible to implement a 32x32 switch scheduler for SLIP on a single chip. 1 Introduction The past few years has seen increasing interest in arbitrary topology cell-based local area networks, such as ATM [5]. In these networks, hosts a...

: 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...

Video service is slated to be a major application of emerging high-speed communications networks of the future. In particular, full-motion video is designed to take advantage of the high bandwidths that will become affordably available with the advent of B-ISDN. A salient feature of compressed video sources is that they give rise to autocorrelated traffic streams, which are difficult to model with traditional modeling techniques. In this paper, we describe a new methodology, called TES (TransformExpand -Sample), for modeling general autocorrelated time series, and we apply it to traffic modeling of compressed video. The main characteristic of this methodology is that it can model an arbitrary marginal distributionand approximate the autocorrelation structure of an empirical sample such as traffic measurements. Furthermore, the empirical marginal (histogram) and leading autocorrelations are captured simultaneously. Practical TES modeling is computationally intensive and is ef...

Abstract — The notion of effective bandwidths has provided a useful practical framework for connection admission control and capacity planning in high-speed communication networks. The associated admissible set with a single linear boundary makes it possible to apply stochastic-loss-network (generalized-Erlang) models for capacity planning. In this paper we consider the case of network nodes that use a priority-service discipline to support multiple classes of service, and we wish to determine an appropriate notion of effective bandwidths. Just as was done previously for the first-in first-out discipline, we use large-buffer asymptotics (large deviations principles) for workload tail probabilities as a theoretical basis. We let each priority class have its own buffer and its own constraint on the probability of buffer overflow. Unfortunately, however, this leads to a constraint for each priority class. Moreover, the large-buffer asymptotic theory with priority classes does not produce an admissible set with linear boundaries, but we show that it nearly does and that a natural bound on the admissible set does have this property. We propose it as an approximation for priority classes. Then there is one linear constraint for each priority class. This linear-admissible-set structure implies a new notion of effective bandwidths, where a given connection is associated with multiple effective bandwidths: one for the priority level of the given connection and one for each lower priority level. This structure can be used regardless of whether the individual effective bandwidths are determined by large-buffer asymptotics or by some other method. 1