Video-conferencing is an efficient tool for distributed collaboration. With the wider availability of broadband wide area networks, such as the Internet2, we can expect an increasing demand for video-conferences conducted over broadband wide area networks. We present a conference control protocol for a highly interactive conference paradigm and its collaboration environment. In such a collaboration environment, a fixed number of channels (three) for multimedia traffic, as well as a common control channel, are used. We propose a conference control protocol that uses a three-channel rotation floor control scheme to coordinate access to the shared media channels and avoid race conditions. Experimental results, as well as the implementation in a research video-conferencing system for wide area networks, show that the proposed protocol can effectively eliminate race conditions while maintaining scalability and reliability.

High quality videoconferencing is an efficient tool for interactive scientific collaboration. With the wide deployment of broadband wide area IP networks such as Intemet2, there is an increasing demand for improved remote collaboration using these networks. In order to make the high quality videoconferencing toolkits for local high-speed networks available over wide area IP networks, issues that are usually insignificant on local area networks must be considered. In this paper, we describe a high quality videoconferencing system we developed based on an earlier version of the system for local area networks. To solve the problems associated with real-time video and audio transmission over wide area IP networks, we added a specifically design hardware device called an adaptation layer translator (ALX). A conference control protocol based on a channel rotation scheme is also developed to coordinate the participants in an ALX-based conference.

We are building a high performance 1.2 Gb/s ATM network interface chip called the APIC (ATM Port Interconnect Controller). In addition to borrowing useful ideas from a number of research and commercial prototypes, the APIC design embraces several innovative features, and integrates all of these pieces into a coherent whole. Some of the novel ideas incorporated in the APIC design include: protected DMA and protected I/O, which allow applications to queue data for transmission or reception directly from user-space, effectively bypassing the kernel. This argues for moving the entire protocol stack including the interface device driver into the user-space, thereby yielding better latency and throughput performance than kernel-resident implementations. Pool DMA when used with packet splitting, is a technique that can be used to build true zero-copy kernel-resident protocol stack implementations, using a page-remapping technique. Finally, orchestrated interrupts and interrupt demultiplexing are mechanisms used to reduce the frequency of interrupts issued by the APIC. Although many of these ideas have been developed in the context of an ATM network interface, we believe they are also applicable in other contexts. In particular, protected DMA and I/O are promising techniques for improving the performance of several different types of I/O devices.

We present the design of a high performance ATM host-network interface for multimedia workstations and servers. At Washington University, as part of an ARPA-sponsored gigabit local ATM testbed, we are building a prototype of this interface that can support a sustained aggregate bidirectional data rate of 2.4 Gbps. The centerpiece of our interface design is a custom chip called the APIC (ATM port interconnect controller). Multiple such chips can be interconnected to yield a desk-area network (DAN) which would serve as a high speed I/O interconnect for the host computer. This paper details the internal design of the APIC chip, and outlines some of its key features. Noteworthy among these are: connection caching, transmit pacing, cell batching, remote control, and support for AAL-0, AAL-5, multipoint, and loopback connections. We have chosen to defer to a later paper the details pertaining to several other features which provide support for zero-copy, improved interrupt handling, direct control of the chip from user-space, and efficient buffering and demultiplexing.

The Washington University MultiMedia eXplorer (MMX) is a complete, host-independent multimedia system capable of transmitting and receiving JPEG-compressed video, CD-quality audio, and high-resolution radiographic images over the Washington University broadband ATM network. If the host is equipped with an ATM interface card, normal network traffic can be supported via an ATM extension port on the MMX. The major components of the MMX are an ATMizer and three multimedia channels. The ATMizer implements the host interface, the interface to the ATM network, and the interface to the three multimedia channels. This paper describes the architecture of the MMX, the software used with the system, and two applications that have been developed to demonstrate the capability of broadband ATM networks for multimedia applications.>

Primary diagnosis plays a central role in the establishment of electronic radiography as a trusted technology. From this technology, other applications in radiology and medicine can easily flow. The fidelity of the electronic presentation of images, the ability of the radiologist to transfer film-based reading skills to a digitally based presentation, and the achievement of improvements in diagnostic efficiency are three important steps to building confidence in electronic methods in radiology. A discussion of these issues is presented as a prelude to the description of a plan for the use of broadband technology and multimedia in electronic radiography, both within and between hospitals.>

Abstract Databse System (ADS) is introduced as a data model in which the notions of symbol and abstraction play a fundemental role in the formal description and structuring of databases. The mechanism of abstraction in ADS is based on the abstraction operator of the lambda calculus. Important concepts in data modeling, such as entity set, entity type, property, attribute, relations, association, constraint, type checking and cardinality, are formally representable in the framework of abstractions on symbols. Thus, the number of primitive concepts in ADS is relatively small. ADS is part of an effort to develop a design methodology for an enduring medical information system, an area where frequent changes in the conceptual schema are anticipated and multi-level abstraction is advantageous.