Lorraine Denby

Assessing network readiness for IP telephony

Networked multimedia applications require stringent real-time QoS guarantees. Successful deployment of such applications closely depends on the performance of the underlying data network. The characteristics and the QoS requirements of these applications are different from traditional data applications. Hence, prior to deployment it is necessary to evaluate a network from a multimedia perspective. In this paper, we focus on IP Telephony and describe a framework for providing tools for IP Telephony readiness evaluation. This framework can be easily generalized to other multimedia applications. Our approach injects synthesized voice traffic and measures perceived end-to-end quality. We present a novel idea of relating voice quality metrics to the performance of data network devices. Following the proposed framework, we developed a prototype tool to evaluate a network and to identify problems, if any, prior to IP Telephony deployment. Our tool automatically discovers the topology of a given network, and collects and integrates network device performance and voice quality metrics. We describe the architecture of our tool and provide sample outputs from a network consisting of 129 devices.

Scalable network assessment for IP telephony

Multimedia applications such as IP telephony are among the applications that demand strict quality of service (QoS) guarantees from the underlying data network. At the predeployment stage it is critical to assess whether the network can handle the QoS requirements of IP telephony and fix problems that may prevent a successful deployment. In this paper we describe a technique for efficiently assessing network readiness for IP telephony. Our technique relies on understanding link level QoS behavior in a network from an IP telephony perspective. We use network topology and end-to-end measurements collected from the network in locating the sources of performance problems that may prevent a successful IP telephony deployment. We present an empirical study conducted on a real network spanning three geographically separated sites of an enterprise network. The empirical results indicate that our approach efficiently and accurately pinpoints links in the network incurring the most significant delay.

Variations on the Histogram

When constructing a histogram, it is common to make all bars the same width. One could also choose to make them all have the same area. These two options have complementary strengths and weaknesses; the equal-width histogram oversmooths in regions of high density, and is poor at identifying sharp peaks; the equal-area histogram oversmooths in regions of low density, and so does not identify outliers. We describe a compromise approach which avoids both of these defects. We regard the histogram as an exploratory device, rather than as an estimate of a density. We argue that relying on the asymptotics of integrated mean squared error leads to inappropriate recommendations for choosing bin-widths. Datasets and R codes are available in the online supplements.

Experiences with evaluating network QoS for IP telephony

Successful deployment of networked multimedia applications such as IP telephony depends on the performance of the underlying data network. QoS requirements of these applications are different from those of traditional data applications. For example, while IP telephony is very sensitive to delay and jitter, traditional data applications are more tolerant of these performance metrics. Consequently, assessing a network to determine whether it can accommodate the stringent QoS requirements of IP telephony becomes critical. We describe a technique for evaluating a network for IP telephony readiness. Our technique relies on the data collection and analysis support of our prototype tool, ExamiNet/spl trade/. It automatically discovers the topology of a given network and collects and integrates network device performance and voice quality metrics. We report the results of assessing the IP telephony readiness of a real network of 31 network devices (routers/switches) and 23 hosts via ExamiNet/spl trade/. Our evaluation identified links in the network that were over utilized to the point at which they could not handle IP telephony.

Statistics in the elementary school

This paper discusses the role of statistics within an interdisciplinary program on real problem solving in elementary schools (through grade 8). We first describe some general features of the USMES (Unified Science and Mathematics for Elementary Schools) curriculum and some situations where the application of statistical principles and techniques can enter the program. Then we present our ideas concerning the kinds of statistical methods that are appropriate in this environment, and we discuss the use of this material with both elementary school students and elementary