Analysis of dependence among size, rate and duration in internet flows

In this paper we examine rigorously the evidence for dependence among data size, transfer rate and duration in Internet flows. We emphasize two statistical approaches for studying dependence, including Pearson's correlation coefficient and the extremal dependence analysis method. We apply these methods to large data sets of packet traces from three networks. Our major results show that Pearson's correlation coefficients between size and duration are much smaller than one might expect. We also find that correlation coefficients between size and rate are generally small and can be strongly affected by applying thresholds to size or duration. Based on Transmission Control Protocol connection startup mechanisms, we argue that thresholds on size should be more useful than thresholds on duration in the analysis of correlations. Using extremal dependence analysis, we draw a similar conclusion, finding remarkable independence for extremal values of size and rate.Comment: Published in at http://dx.doi.org/10.1214/09-AOAS268 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

17th IEEE Real-Time Systems Symposium: Work in Progress Sessions

The Table of Contents for the workshop is contained in 1996-027-00main.pdfDear Colleagues: This year marks the beginning of a new tradition within the Real-Time Systems Symposium, that of holding special sessions for the presentation of new and on-going projects in real-time systems. The prime purpose of these Work In Progress (WIP) sessions is to provide researchers in Academia and Industry an opportunity to discuss their evolving ideas and gather feedback thereon from the real-time community at large. The idea of holding these sessions is timely, and I am pleased to report that this year RTSS'96 WIP received 22 submissions, of which 14 have been accepted for presentation during the symposium and for inclusion in RTSS'96 WIP proceedings. Many people worked hard to make the idea of holding the WIP sessions a reality. In particular, I would like to thank Sang Son for his hard work in accommodating the WIP sessions within the busy schedule of RTSS'96. Also, I would like to thank all members of the RTSS'96 Program Committee, Al Mok and Doug Locke in particular, for their encouragement and constructive feedback regarding the organization of these sessions. Finally, I would like to thank all those who submitted their work to RTSS'96 WIP and those from RTSS'96 program committee who helped review these submissions. I hope these sessions will prove beneficial, both to the WIP presenters and to RTSS'96 attendees. Azer Bestavros RTSS'96 WIP Chair December 1996.IEEE-CS TC-RT

The Rate-Based Execution Model

We present a new task model for the real-time execution of event-driven tasks in which no a priori characterization of the actual arrival rates of events is known; only the expected arrival rates of events is known. We call this new task model rate-based execution (RBE), and it is a generalization of the common sporadic task model. The RBE model is motivated naturally by distributed multimedia and digital signal processing applications. We identify necessary and sufficient conditions for determining the feasibility of an RBE task set, and an optimal scheduling algorithm (based on preemptive earliest-deadline-first (EDF) scheduling) for scheduling the execution of an RBE task set. With respect to the class of work-conserving scheduling algorithms (i.e., the class of scheduling algorithms that schedule without inserting idle time in the schedule), we present necessary and sufficient feasibility conditions and optimal algorithms for non-preemptive scheduling and preemptive scheduling with shared resources

Towards a Better-Than-Best-Effort Forwarding Service for Multimedia Flows

Introduction & Motivation Our research at UNC concerns the management of multimedia and more general continuous-media flows across the Internet. We focus on network support for (highly) interactive applications where real-time transmission is essential for the correct operation of the application. Such applications include teleimmersion applications and interactive distributed virtual environments. In these applications minimum possible end-to-end transmission delay is required for effective device control and for maintaining the sense of immersion in a virtual world [1, 2]. To realize the performance requirements of these and other real-time multimedia applications, end-system media adaptation techniques are commonly employed to ameliorate the effects of contention for bandwidth and other resources in the network. Most multimedia and virtual environment systems, including the ones we consider, are capable of adapting to modest changes in end-to-end network delay and throughp

The Real-Time Producer/Consumer Paradigm: A paradigm for the construction of efficient, predictable real-time systems

: A concurrent programming system for constructing hard-real-time applications is described. The system is based on a novel semantics of inter-process communication called the real-time producer/consumer (RTP/C) paradigm. Process interactions are modeled as producer/ consumer systems with a timing constraint on the rate at which the consumer must service the producer. The RTP/C paradigm provides a framework both for expressing processor-time-dependent computations and for reasoning about the real-time behavior of programs. A formal model of processor and resource allocation is used to determine necessary and sufficient conditions for realizing the RTP/C semantics of a program. The design of an interactive graphics system illustrates the use of the system. Introduction Real-time computer systems are loosely defined as the class of computer systems that must perform computations and I/O operations in a time-frame defined by processes in the environment external to the computer. Real-time..

On kernel support for real-time multimedia applications

Abstract: Real-time operating system services are required to support multimedia systems that rely heavily of the workstation processor for control of the audio and video processors and movement of audio and video data. Such services are typically not available in existing workstation operating systems. This note comments on the requirements for such services and briefly describes the YARTOS kernel; an operating system kernel that provides real-time communication and computation services