Network Calculus Theory Research Articles

Real-time performance evaluation of line topology switched Ethernet

Recently, switched Ethernet has become an active area of research because of its wide uses in industry. However, its uses have various real-time constraints on data communications. This paper analyzes the performance of the line topology switched Ethernet as a data acquisition network. Network calculus theory, which has been successfully applied to assess the real-time performance of packet-switched networks, is used to analyze the networks. To properly describe the activity of switches, a novel approach of modeling data flows into or out of switches is addressed. Based on our model, a concisely analytical expression of the maximal end-to-end delay in line topology switched Ethernet is derived. Finally, the relative simulation results are demonstrated. These results agree well with the analytical results, and thus they validate the data flow modeling techniques.

New perspectives on network calculus

Originated in communications engineering and theoretically rooted in idempotent analysis, the theory of network calculus (NetCal) presents an elegant methodology for offering performance guarantees in deterministic queuing systems. In this research we developed two new formulations of Net-Cal, each of which bears some unique insights. A fuzzy formulation maps NetCal's (min,+) convolution operator to the addition of fuzzy numbers. A conjugate perspective based on the notion of Legendre transform leads to a new NetCal formulation to be termed as CT-NetCal, which possesses some distinct advantages in modeling, computation and interpretation.

Worst Case Modelling of Wireless Sensor Networks

Until recently, it has been hard to obtain a predictable performance from wireless sensor networks, not to mention performance guarantees. In particular, a widely accepted and established methodology for modelling the performance of wireless sensor networks is missing. In the last three years we have made a step into the direction of an analytical framework for the performance modelling of wireless sensor networks based on the theory of network calculus, which we customized towards a so-called sensor network calculus [Jens B. Schmitt and Utz Roedig: Sensor Network Calculus – A Framework for Worst Case Analysis. In: Proc. of IEEE/ACM Int. Conf. on Distributed Computing in Sensor Systems (DCOSS '05), pages 141-154. Springer, LNCS 3560, June 2005.]. We believe the sensor network calculus to be especially useful for applications which have timing requirements. Examples for this class of applications are factory control, nuclear power plant control, medical applications, and any alerting systems. In general, whenever the sensed input may necessitate immediate actions, the sensor network calculus may be the way to go. In this paper we summarize these activities and discuss the open issues for such an analytical framework to be widely accepted.

Rate-interval curves — A tool for the analysis and monitoring of network traffic

In this paper we propose a method, related to the theory of Network Calculus, for the analysis of aggregate network traffic by means of empirical rate-interval curves obtained from experimental data. The algorithm on which it is based differs from the commonly employed wavelet-based approach, although it retains some of its multiresolution features. We briefly introduce the theoretical aspects, analyze measurement accuracy and present results, obtained both by simulation and by the analysis of real traffic traces, which provide an assessment of the strengths and weaknesses of the proposed method. Rate-interval curve analysis provides very robust and acceptably accurate estimates of the Hurst parameter value and, even in the presence of flow irregularities, results can be proved to be correct as far as scaling properties are concerned. Further analyzes concerning peaks, bursts and similar localized phenomena that may have a significant impact on the performances of a network are allowed by considering maximal rate envelopes, showing the potential of this approach for monitoring applications.

NETWORK CALCULUS BASED FDI APPROACH FOR SWITCHED ETHERNET ARCHITECTURE

: The Networked Control Systems (NCS) are complex systems which integrate information provided by several domians such as automatic control, computer science, communication network. The work presented in this paper concerns fault detection, isolation and compensation of communication network. The proposed method is based on the classical approach of Fault Detection and Isolation and Fault Tolerant Control (FDI/FTC) currently used in diagnosis. The modelling of the network to be supervised is based on both couloured petri nets and network calculus theory often used to represent and analyse the network behaviour. The goal is to implement inside network devices algorithms enabling to detect, isolate and compensate communication faults in an autonomous way.

USE OF UPPER BOUND DELAY ESTIMATE IN STABILITY ANALYSIS AND ROBUST CONTROL COMPENSATION IN NETWORKED CONTROL SYSTEMS

Recent interest in networked control systems (NCS) has instigated research in various areas of both communication networks and control. The analysis of NCS has often been performed either from the network, or the control point of view and not many papers exist were the analysis of both is done in the same context. Here an overall analysis is presented. In the paper the procedure of obtaining the upper bound delay value in the switched Ethernet network is proposed and the obtained delay estimate is used in stability analysis of the feedback loop and in the control compensation. The upper bound delay algorithm is based on the network calculus theory, the stability analysis uses the small gain theorem, and control compensating strategy is based on Smith predictor, where however the upper bound delay is utilised in obtaining the delay estimate.

Graceful degradation of loss-tolerant QoS using ( m, k)-firm constraints in guaranteed rate networks

The Weighted Fair Queueing (WFQ) scheduling algorithm and its variants can be used to provide real-time guarantees by making bandwidth reservation. However, while hard guarantees are based on a peak workload model that leads to underutilize network resources, soft guarantees, based on average workload model, are not always sufficient to maintain acceptable Quality-of-Service (QoS) since consecutive packet losses or deadline misses may occur, which are not suitable for real-time applications. In this paper, we propose a trade-off between hard and soft real-time guarantees to maintain an acceptable QoS in overload conditions and efficiently maximize the utilization of network resources. The key to our solution is based on the fact that many real-time applications, such as voice and video, are loss-tolerant. The loss profile must be well defined, and such a profile can be easily specified using the ( m, k)-firm model. Therefore, we propose the ( m, k)-WFQ algorithm to take into account ( m, k)-firm timing constraints to provide delay guarantees of at least m packets out of any k consecutive packets without violating bandwidth fairness or misusing network resources. Using the Network Calculus theory, an analytic study gives the deterministic delay bound provided by the ( m, k)-WFQ algorithm for upper bounded arrival curve traffic. We extend our analytic results for guaranteed-rate networks, such as the IntServ QoS model and ATM networks, and the DiffServ QoS model. Analytic results and simulations show a noticeable improvement in delay guarantee made by ( m, k)-WFQ compared to WFQ without much degradation of bandwidth fairness.

VALIDATION OF THE NETWORK CALCULUS APPROACH FOR THE PERFORMANCE EVALUATION OF SWITCHED ETHERNET BASED INDUSTRIAL COMMUNICATIONS

The objective of this work is to validate the modelling of a switched Ethernet architecture in order to be able to evaluate the maximum end to end delays. The major interest is to apply these results in an industrial or technical context, where some of the communications are strongly time-constrained. This paper describes a model of an Ethernet switch. It also presents the analytical formulas issued from the Network Calculus theory which upper bound the maximum time for crossing such a switch, and an algorithm to determine the maximum end to end delays of the time-critical messages over the whole network. This work is validated by an experimental application which proves that the worst case estimated by the Network Calculus can be really reached and that this method is not so pessimistic.

Theories and models for Internet quality of service

We survey advances in theories and models for Internet quality of service (QoS). We start with the theory of network calculus, which lays the foundation for support of deterministic performance guarantees in networks, and illustrate its applications to integrated services, differentiated services, and streaming media playback delays. We also present mechanisms and architecture for scalable support of guaranteed services in the Internet, based on the concept of a stateless core. Methods for scalable control operations are also discussed. We then turn our attention to statistical performance guarantees and describe several new probabilistic results that can be used for a statistical dimensioning of differentiated services. Lastly, we review proposals and results in supporting performance guarantees in a best effort context. These include models for elastic throughput guarantees based on TCP performance modeling, techniques for some QoS differentiation without access control, and methods that allow an application to control the performance it receives, in the absence of network support.