Computing infrastructure issues in distributed communications systems : a survey of operating system transport system architectures

The performance of distributed applications (such as file transfer, remote login, tele-conferencing, full-motion video, and scientific visualization) is influenced by several factors that interact in complex ways. In particular, application performance is significantly affected both by communication infrastructure factors and computing infrastructure factors. Several communication infrastructure factors include channel speed, bit-error rate, and congestion at intermediate switching nodes. Computing infrastructure factors include (among other things) both protocol processing activities (such as connection management, flow control, error detection, and retransmission) and general operating system factors (such as memory latency, CPU speed, interrupt and context switching overhead, process architecture, and message buffering). Due to a several orders of magnitude increase in network channel speed and an increase in application diversity, performance bottlenecks are shifting from the network factors to the transport system factors.This paper defines an abstraction called an "Operating System Transport System Architecture" (OSTSA) that is used to classify the major components and services in the computing infrastructure. End-to-end network protocols such as TCP, TP4, VMTP, XTP, and Delta-t typically run on general-purpose computers, where they utilize various operating system resources such as processors, virtual memory, and network controllers. The OSTSA provides services that integrate these resources to support distributed applications running on local and wide area networks.A taxonomy is presented to evaluate OSTSAs in terms of their support for protocol processing activities. We use this taxonomy to compare and contrast five general-purpose commercial and experimental operating systems including System V UNIX, BSD UNIX, the x-kernel, Choices, and Xinu

The QUIC Fix for Optimal Video Streaming

Within a few years of its introduction, QUIC has gained traction: a significant chunk of traffic is now delivered over QUIC. The networking community is actively engaged in debating the fairness, performance, and applicability of QUIC for various use cases, but these debates are centered around a narrow, common theme: how does the new reliable transport built on top of UDP fare in different scenarios? Support for unreliable delivery in QUIC remains largely unexplored. The option for delivering content unreliably, as in a best-effort model, deserves the QUIC designers' and community's attention. We propose extending QUIC to support unreliable streams and present a simple approach for implementation. We discuss a simple use case of video streaming---an application that dominates the overall Internet traffic---that can leverage the unreliable streams and potentially bring immense benefits to network operators and content providers. To this end, we present a prototype implementation that, by using both the reliable and unreliable streams in QUIC, outperforms both TCP and QUIC in our evaluations.Comment: Published to ACM CoNEXT Workshop on the Evolution, Performance, and Interoperability of QUIC (EPIQ

Clock Hierarchies: An Abstraction for Grouping and controlling Media Systems

Synchronization plays an important role in multimedia systems at various levels of abstraction. In this paper, we propose a set of powerful abstractions for controlling and synchronizing continuous media streams in distributed environments. The proposed abstractions are based on a very general computation model, which allows media streams to be processed (i.e. produced, consumed or transformed) by arbitrarily structured networks of linked components. Further, compound components can be composed of existing ones to provide higher levels of abstractions. The clock abstraction is provided to control individual media streams, i.e. streams can be started, paused or scaled by issuing the appropriate clock operations. Clock hierarchies are used to hierarchically group related streams, where each clock in the hierarchy identifies and controls a certain (sub)group of streams. Control and synchronization requirements can be expressed in a uniform manner by associating group members with control or sync attributes. An important property of the concept of clock hierarchies is that it can be combined in a natural way with component nesting

Self-modifiable color petri nets for modeling user manipulation and network event handling

A Self-Modifiable Color Petri Net (SMCPN) which has multimedia synchronization capability and the ability to model user manipulation and network event (i.e. network congestion, etc.) handling is proposed in this paper. In SMCPN, there are two types of tokens: resource tokens representing resources to be presented and color tokens with two sub-types: one associated with some commands to modify the net mechanism in operation, another associated with a number to decide iteration times. Also introduced is a new type of resource token named reverse token that moves to the opposite direction of arcs. When user manipulation/network event occurs, color tokens associated with the corresponding interrupt handling commands will be injected into places that contain resource tokens. These commands are then executed to handle the user manipulation/network event. SMCPN has the desired general programmability in the following sense: 1) It allows handling of user manipulations or pre-specified events at any time while keeping the Petri net design simple and easy. 2) It allows the user to customize event handling beforehand. This means the system being modeled can handle not only commonly seen user interrupts (e.g. skip, reverse, freeze), the user is free to define new operations including network event handling. 3) It has the power to simulate self-modifying protocols. A simulator has been built to demonstrate the feasibility of SMCPN

The multidriver: A reliable multicast service using the Xpress Transfer Protocol

A reliable multicast facility extends traditional point-to-point virtual circuit reliability to one-to-many communication. Such services can provide more efficient use of network resources, a powerful distributed name binding capability, and reduced latency in multidestination message delivery. These benefits will be especially valuable in real-time environments where reliable multicast can enable new applications and increase the availability and the reliability of data and services. We present a unique multicast service that exploits features in the next-generation, real-time transfer layer protocol, the Xpress Transfer Protocol (XTP). In its reliable mode, the service offers error, flow, and rate-controlled multidestination delivery of arbitrary-sized messages, with provision for the coordination of reliable reverse channels. Performance measurements on a single-segment Proteon ProNET-4 4 Mbps 802.5 token ring with heterogeneous nodes are discussed

Adaptive Synchronization of Semantically Compressed Instructional Videos for Collaborative Distance Learning

The increasing popularity of online courses has highlighted the need for collaborative learning tools for student groups. In addition, the introduction of lecture videos into the online curriculum has drawn attention to the disparity in the network resources available to students. We present an e-Learning architecture and adaptation model called AI2TV (Adaptive Interactive Internet Team Video), which allows groups of students to collaboratively view a video in synchrony. AI2TV upholds the invariant that each student will view semantically equivalent content at all times. A semantic compression model is developed to provide instructional videos at different level-of-details to accommodate dynamic network conditions and usersäó» system requirements. We take advantage of the semantic compression algorithmäó»s ability to provide different layers of semantically equivalent video by adapting the client to play at the appropriate layer that provides the client with the richest possible viewing experience. Video player actions, like play, pause and stop, can be initiated by any group member and and the results of those actions are synchronized with all the other students. These features allow students to review a lecture video in tandem, facilitating the learning process. Experimental trials show that AI2TV successfully synchronizes instructional videos for distributed students while concurrently optimizing the video quality, even under conditions of fluctuating bandwidth, by adaptively adjusting the quality level for each student while still maintaining the invariant