The current model for multicast transmission of video over the Internet assumes that a fixed average bandwidth is uniformly present throughout the network. Consequently, sources limit their transmission rates to accommodate the lowest bandwidth links, even though high-bandwidth connectivity might be available to many of the participants. We propose an architecture where a video transmission can be decomposed into multiple sessions with different bandwidth requirements using an application-level gateway. Our video gateway transparently connects pairs of sessions into a single logical conference by manipulating the data and control information of the video streams. In particular, the gateway performs bandwidth adaptation through transcoding and rate-control. We describe an efficient algorithm for transcoding Motion-JPEG to H.261 that runs in real-time on standard workstations. By making the Real-time Transport Protocol (RTP) an integral component of our architecture, the video gateway in...

In recent years, the "Internet Multicast Backbone," or MBone, has risen from a small, research curiosity to a largescale 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 efficient software implementation) and high loss resilience (admitting robust operation in loosely controlled environments like the Internet) . 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.

In just a few 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 our development of multipoint audio, video, and shared whiteboard conferencing applications that are now used daily by the large and growing MBone community. Because these real-time media are transmitted at a uniform rate to all the receivers in the network, the source must either run below the bottleneck rate or overload portions of the multicast distribution tree. In this dissertation, we propose a solution to this problem 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 distr...

The Application Level Framing (ALF) protocol architecture [2] encourages application control over mechanisms that traditionally fall within the "transport layer", e.g., loss detection and recovery. Traditional ARQ-based reliable protocols for unicast (e.g., TCP) as well as multicast (e.g., Horus [30], RMTP [15], etc.) number data units sequentially to detect losses. Unfortunately, these transport-level sequence numbers do not permit receivers to flexibly tailor their reliability semantics. Achieving receiver-driven reliability is cumbersome in the existing "layered" architecture of the network protocol stack where the receiving application has no knowledge of how application-level objects map onto transport level sequence numbers. In this paper, we propose a new data naming scheme that exposes the structure of application data to the transport layer, thereby enhancing the expressibility of an applications' reliability and ordering semantics. We apply this data naming scheme to a reliab...

In this survey article we describe the roots of IP Multicast in the Internet, the evolution of the Internet Multicast Backbone or “MBone,” and the technologies that have risen around the MBone to support large-scale Internet-based multimedia conferencing. We develop the technical rationale for the design decisions that underly the MBone tools, describe the evolution of this work from early prototypes into Internet standards, and outline the open challenges that remain and must be overcome to realize a ubiquitous multicast infrastructure. We and others in the MBone research community have implemented our protocols and methods in “real” applications and have deployed a fully operational system on a very large scale over the MBone. This infrastructure — including our audio, video, shared whiteboard tools and protocols — is now in daily use by the large and growing MBone user and research communities and the success and utility of this approach has resulted in commercialization of many of the underlying technologies.

A Framework for Interactive Multicast Data Transport in the Internet by Suchitra Raman Doctor of Philosophy in Computer Science University of California at Berkeley Professor Steven R. McCanne, Chair The remarkable growth of the Internet as the a data transmission medium has in part been enabled by the simplicity and scalability of the core Internet Protocol (IP), which is used for addressing and routing unicast data packets through the network. The IP service model does not provide any packet delivery guarantees, but rather provides a "best-effort" contract, and leaves it to higher layers to provide enhanced services using this basic service. Today, the de facto transport protocol on the Internet is the Transmission Control Protocol (TCP) [109, 128]. TCP was designed primarily for applications such as telnet, a remote terminal application, and ftp, a file transfer application, which require data to be delivered reliably and in an ordered manner. While the TCP abstraction and pro...

Large-scale, multi-point, multimedia conferencing applications designed to facilitate long-distance collaboration are enjoying growing popularity. Usually composed of real-time audio, video and shared-drawing applications, these collaborative environments help render the geographical location of collaborators irrelevant. To complement these existing collaborative applications, it would be useful to have the ability to distribute documents synchronously over the World Wide Web (WWW). One model for synchronized information dissemination within the Web is webcasting in which data are simultaneously distributed to multiple destinations. The WWW's traditional unicast client/server communication model suers, however, when applied to webcasting; solutions which require many clients to simultaneously fetch data from the origin server using the client/server model will likely cause server and link overload. A number of webcasting solutions have been proposed. Many have limited scalability bec...

An enduring trait of the Internet is its heterogeneity. Evidence of this heterogeneity includes the wide range of network transmission rates, varying across many orders of magnitude, and the vast differences in computing power, ranging from PDA's to supercomputers. These heterogeneities present significant barriers to the transmission of real-time multimedia data across groups. The barriers stem from the fact that in order to accommodate the entire gamut of group member characteristics, e.g., bandwidth availability or computing power, a source is required to transmit its data with properties matching the most constrained receiver. Instead, we would like to transmit media to multiple receivers at heterogeneous rates and properties tha...

A common approach to experimental multimedia network applications is to structure a range of media tools as independent monolithic applications. In this approach, every change must be incorporated into the appropriate applications, requiring each to be entirely recompiled and then redistributed to users. To simplify this procedure, we decompose the tools into reusable and flexible components, much like those provided in existing multimedia toolkits, such as Berkeley's Continuous Multimedia Toolkit and MIT's VuSystem which offer application developers a set of predefined modular building blocks that can be arranged as sources, sinks, and filters for media-data. With a well-decomposed and easy-to-understand object architecture, application developers can glue together components with simple scripts. Objects can be added or tailored to meet specific needs and then easily reassembled in a plug-and-play environment to create new tools. A clean object decomposition also makes it possible to ...

Several compressionschemesfor Internet video utilize block-based conditional replenishment (CR) where block updates are coded independently of the past. In the current Internet video tools, blocks are compressed with a single-layer representation. We propose a new approach that compressesimage blocks using a layered representation. Our Layered-DCT (LDCT) compression algorithm, derived from progressive JPEG, has been combined with CR and optimized for efficient software implementation to provide an improved solution for Internet packet video. Although LDCT is constrained to a layered representation, its compressionperformance is as good or better than the single layer Intra-H.261 and baseline JPEG coding schemes. 1. INTRODUCTION Large-scale, real-time multipoint video distribution has become a commonlyusedcommunicationsmedium in the Internet. Although the deployment of IP Multicast [3] provides a mechanism for efficiently transmitting a packetized video stream to large numbers of rec...