Transport System Architecture Services for High-Performance Communications Systems Douglas C. Schmidt and Tatsuya Suda Department of Information and Computer Science, University of California, Irvine Irvine, CA 92717, U.S.A. Abstract Providing end-to-end gigabit communication support for high-bandwidth multimedia applications re- quires transport systems that transfer data efficiently via network protocols such as TCP, TP4, XTP, and ST- II. This paper describes and classifies transport system services that integrate operating system resources such as CPU(s), virtual memory, and I/O devices together with network protocols to support distributed multimedia applications running on local and wide area networks. A taxonomy is presented that compares and evaluates four commercial and experimental transport systems in terms of their protocol processing support. The systems covered in this paper include System V UNIX STREAMS, the BSD UNIX networking subsystem, the x-kernel, and the Choices Conduit system. This paper is intended to navigate researchers and developers through the transport system design space by describing alternative approaches for key transport system services. 1 Introduction Transport systems integrate operating system services (such as memory and process management) together with communication protocol processing mechanisms (such as connection management, data transmission control, and error protection) to support distributed applications running on local and wide area networks. The demand for many types of distributed multimedia applications 1 is expanding rapidly, and application requirements and usage patterns are undergoing significant changes. When coupled with the increased chan- nel speeds and services offered by high-performance networks, these changes are taxing the capabilities of existing transport systems to process application data at the network channel speeds. This paper examines six key transport system services that support bandwidth-intensive, multimedia appli- cations such as medical imaging, scientific visualization, full-motion video, and tele-conferencing. These ap- plications possess quality-of-service (QoS) requirements that differ greatly from traditional data applications such as remote login, email, and file transfer. For example, multimedia applications involve combinations of requirements such as extremely high throughput (full-motion video), strict real-time delivery (manufac- turing control systems), low latency (on-line transaction processing), low delay jitter (voice conversation), capabilities for multicast (collaborative work activities) and broadcast (distributed name resolution), high- reliability (bulk data transfer), temporal synchronization (tele-conferencing), and some degree of loss toler- ance (hierarchically-coded video). Applications also impose different network traffic patterns. For instance, some applications generate highly bursty traffic (variable bit-rate video), some generate continuous traffic (constant bit-rate video), and others generate short, interactive, request-response traffic (network file systems using remote procedure calls (RPC)). An earlier version of this paper appeared in the IEEE Journal on Select Areas in Communication in July 1993. 1 We refer to these as simply “applications” from now on. 1