On Class-based Isolation of UDP, Short-lived and Long-lived TCP Flows

The congestion control mechanisms of TCP make it vulnerable in an environment where flows with different congestion-sensitivity compete for scarce resources. With the increasing amount of unresponsive UDP traffic in today's Internet, new mechanisms are needed to enforce fairness in the core of the network. We propose a scalable Diffserv-like architecture, where flows with different characteristics are classified into separate service queues at the routers. Such class-based isolation provides protection so that flows with different characteristics do not negatively impact one another. In this study, we examine different aspects of UDP and TCP interaction and possible gains from segregating UDP and TCP into different classes. We also investigate the utility of further segregating TCP flows into two classes, which are class of short and class of long flows. Results are obtained analytically for both Tail-drop and Random Early Drop (RED) routers. Class-based isolation have the following salient features: (1) better fairness, (2) improved predictability for all kinds of flows, (3) lower transmission delay for delay-sensitive flows, and (4) better control over Quality of Service (QoS) of a particular traffic type.

The Practice and Understanding of the Eucharist in the United Church of Christ: A Practical Theological Study

This dissertation explores the complexity of the understanding and practice of the Eucharist in the United Church of Christ as revealed in a textual analysis of the UCC Book of Worship (1986) and a qualitative study of five representative UCC congregations. Little has been written on this topic, save for several brief articles on the history of the theology of the sacrament in the two bodies that merged to form the UCC in 1957: the Congregational Christian Churches (CC) and the Evangelical and Reformed Church (E&R). This dissertation advances the topic through a practical-theological study that brings into critical conversation contemporary eucharistic practices in five congregations and a historical theological analysis of liturgical traditions in the UCC and antecedent denominations. Through this conversation, the study articulates common themes of a UCC eucharistic theology and explores implications for ongoing theology and practice in the denomination. The introduction explicates the methodology employed in this study, guided by Don Browning's work. The first two chapters present the findings of the focus group interviews and an interpretation of those results respectively. Chapter three analyzes the eucharistic liturgies in three historic books of worship used in the E&R heritage. In chapter four, two of the antecedent resources utilized in the CC tradition are analyzed. The short-lived Hymnal of the United Church of Christ, published in 1974, includes liturgies that would find fuller expression in the 1986 Book of Worship. That hymnal is examined in chapter five. Chapter six interprets the two services of "Word and Sacrament" found in the Book of Worship. Chapter seven offers a comparative analysis of the focus group findings and the theology inherent in the Book of Worship. The final chapter offers strategic recommendations for revised theory and practice. The conclusion points toward areas for further research: it propels a critical conversation around the notion of covenant, Christ's presence in the meal, and who can receive and officiate at the Eucharist. This dissertation concludes that the UCC lives within a balance of multiple, complementary theologies and challenges the denomination to make stronger connections between the meal and mission, reconciliation, and tradition.

Structural Analysis of Network Traffic Flows

Network traffic arises from the superposition of Origin-Destination (OD) flows. Hence, a thorough understanding of OD flows is essential for modeling network traffic, and for addressing a wide variety of problems including traffic engineering, traffic matrix estimation, capacity planning, forecasting and anomaly detection. However, to date, OD flows have not been closely studied, and there is very little known about their properties. We present the first analysis of complete sets of OD flow timeseries, taken from two different backbone networks (Abilene and Sprint-Europe). Using Principal Component Analysis (PCA), we find that the set of OD flows has small intrinsic dimension. In fact, even in a network with over a hundred OD flows, these flows can be accurately modeled in time using a small number (10 or less) of independent components or dimensions. We also show how to use PCA to systematically decompose the structure of OD flow timeseries into three main constituents: common periodic trends, short-lived bursts, and noise. We provide insight into how the various constituents contribute to the overall structure of OD flows and explore the extent to which this decomposition varies over time.

Communicable Memory and Lazy Barriers for Bulk Synchronous Parallelism in BSPk

Communication and synchronization stand as the dual bottlenecks in the performance of parallel systems, and especially those that attempt to alleviate the programming burden by incurring overhead in these two domains. We formulate the notions of communicable memory and lazy barriers to help achieve efficient communication and synchronization. These concepts are developed in the context of BSPk, a toolkit library for programming networks of workstations|and other distributed memory architectures in general|based on the Bulk Synchronous Parallel (BSP) model. BSPk emphasizes efficiency in communication by minimizing local memory-to-memory copying, and in barrier synchronization by not forcing a process to wait unless it needs remote data. Both the message passing (MP) and distributed shared memory (DSM) programming styles are supported in BSPk. MP helps processes efficiently exchange short-lived unnamed data values, when the identity of either the sender or receiver is known to the other party. By contrast, DSM supports communication between processes that may be mutually anonymous, so long as they can agree on variable names in which to store shared temporary or long-lived data.