Using reliable multicast for caching and collaboration within the world wide web

Journal ArticleThe World Wide Web has become an important medium for information dissemination. One model for synchronized information dissemination within the Web is webcasting in which data are simultaneously distributed to multiple destinations. The Web's traditional unicast client/server communication model suffers, however, when applied to webcasting; approaches that require many clients to simultaneously fetch data from the origin server using the client/server model will likely cause server and link overload. In this paper we describe a webcast design that improves upon previous designs by leveraging application level framing (ALF) design methodology. We build upon the Scalable Reliable Multicast (SRM) framework, which is based upon ALF, to create a custom protocol to meet webcast's scalability needs. We employ the protocol in an architecture consisting of two reusable components: a webcache component and a browser control component. We have implemented our design using a new SRM library called libsrm. We present the results of a simple performance evaluation and report on lessons learned while using libsrm

Low-complexity video coding for receiver-driven layered multicast

In recent years, the “Internet Multicast Backbone,” or MBone, has risen from a small, research curiosity to a large- scale and widely used communications infrastructure. A driving force behind this growth was the development of multipoint audio, video, and shared whiteboard conferencing applications. Because these real-time media are transmitted at a uniform rate to all of the receivers in the network, a source must either run at the bottleneck rate or overload portions of its multicast distribution tree. We overcome this limitation by moving the burden of rate adaptation from the source to the receivers with a scheme we call receiver-driven layered multicast, or RLM. In RLM, a source distributes a hierarchical signal by striping the different layers across multiple multicast groups, and receivers adjust their reception rate by simply joining and leaving multicast groups. In this paper, we describe a layered video compression algorithm which, when combined with RLM, provides a comprehensive solution for scalable multicast video transmission in heterogeneous networks. In addition to a layered representation, our coder has low complexity (admitting an effi- cient software implementation) and high loss resilience (admitting robust operation in loosely controlled environments like the Inter- net). Even with these constraints, our hybrid DCT/wavelet-based coder exhibits good compression performance. It outperforms all publicly available Internet video codecs while maintaining comparable run-time performance. We have implemented our coder in a “real” application—the UCB/LBL videoconferencing tool vic. Unlike previous work on layered video compression and transmission, we have built a fully operational system that is currently being deployed on a very large scale over the MBone

Soft ARQ for layered streaming media

A growing and important class of traffic in the Internet is so-called `streaming media,' in which a server transmits a packetized multimedia signal to a receiver that buffers the packets for playback. This playback buffer, if adequately sized, counteracts the adverse impact of delay jitter and reordering suffered by packets as they traverse the network, and if large enough also allows lost packets to be retransmitted before their playback deadline expires. We call this framework for retransmitting lost streaming-media packets `soft ARQ' since it represents a relaxed form of Automatic Repeat reQuest (ARQ). While state-of-the-art media servers employ such strategies, no work to date has proposed an optimal strategy for delay-constrained retransmissions of streaming media-specifically, one which determines what is the optimal packet to transmit at any given point in time. In this paper, we address this issue and present a framework for streaming media retransmission based on layered media representations, in which a signal is decomposed into a discrete number of layers and each successive layer provides enhanced quality. In our approach, the source chooses between transmitting (1) newer but critical coarse information (e.g., a first approximation of the media signal) and (2) older but less important refinement reformation (e.g., added details) using a decision process that minimizes the expected signal distortion at the receiver. To arrive at the proper mix of these two extreme strategies, we derive an optimal strategy for transmitting layered data over a binary erasure channel with instantaneous feedback. To provide a quantitative performance comparison of different transmission policies, we conduct a Markov-chain analysis, which shows that the best transmission policy is time-invariant and thus does not change as the frames' layers approach their expiration times

I/O Is Faster Than the CPU - Let's Partition Resources and Eliminate (Most) OS Abstractions

Peer reviewe

A Distributed Whiteboard for Network Conferencing

Advances in network technology and research in real-time packet-switched networks have prompted the emergence of internet conferencing. While audio and video conferencing tools are readily available, shared workspaces and drawing tools have been slower to emerge. We present a design for a network conferencing whiteboard that differs in notable respects from other shared workspace prototypes. We describe its transport layer, based on IP multicasting and application level framing, and its object oriented imaging model, based on persistent PostScript graphics operations. We then propose a user interface, and finally, describe a C++ implementation based on the InterViews structured graphics library. 1 Introduction In the early days of the Internet, experiments with packet voice proved that computer networks could be used for integrated services [5]. However, the technological limitations of the time made such use impractical. This is now changing. Dramatic advances in network bandwidth an..