Most operating systems use interface interrupts to schedule network tasks. Interrupt-driven systems can provide low overhead and good latency at low of-fered load, but degrade significantly at higher arrival rates unless care is taken to prevent several pathologies. These are various forms of receive livelock, in which the system spends all its time processing interrupts, to the exclusion of other neces-sary tasks. Under extreme conditions, no packets are delivered to the user application or the output of the system. To avoid livelock and related problems, an operat-ing system must schedule network interrupt handling as carefully as it schedules process execution. We modified an interrupt-driven networking implemen-tation to do so; this eliminates receive livelock without degrading other aspects of system performance. We present measurements demonstrating the success of our approach. 1.

Many future applications will require guarantees on network performance, such as bounds on throughput, delay, delay jitter, and reliability. To address this need, the Tenet Group at the University of California at Berkeley has designed, simulated, and implemented a suite of network protocols to support real-time channels (network connections with mathematically provable performance guarantees). The protocols, which constitute the prototype Tenet Real-Time Protocol Suite (Suite 1), run on a packet-switching internetwork, and can coexist with the popular Internet Suite. We rely on the use of connection-oriented communication, admission control, and channel rate control. This protocol suite is the first complete set of communication protocols that can transfer real-time streams with guaranteed quality in packet-switching internetworks. Our initial development was done on a local-area FDDI network. We have since installed our protocols on the experimental wide-area internetwork of Project ...

The Multimedia Multicast Channel is a dissemination-oriented communication abstraction providing a service analogous to that of a cable television broadcast channel. A source transmits multimedia information such as video and audio streams onto a channel, and a varying number of receivers "tune in" to the channel to receive a selected set of the streams. To support heterogeneity, each receiver may tailor the selected streams to meet individual needs through the use of filters. The design encourages a very loose coupling between the source and the receivers, promoting open-loop control for the underlying network protocols. KEY WORDS: multicast, multimedia, dissemination, computer networks. This research has been supported in part by grants from DEC, IBM, NCR, NSF, TRW, and UC MICRO. The views expressed are those of the authors, and not necessarily those of the supporters. 1 Introduction The Multimedia Multicast Channel (MMC) is a programming abstraction which supports dissemination...

With the demand for multimedia and computational science applications, guaranteed performance communication services have become a necessary feature of future high-speed networks. These communications services should possess a high level of sophistication so that they can easily adapt the network to the wide variety of applications soon to be seen, thereby allowing the network to increase its availability and flexibility. Availability is the ability of the network to accommodate as many real-time clients as possible without violating any client's performance guarantees, while flexibility is the ability to adapt to changing network state and client demands in order to maintain the performance guarantees and quality of service promised to the client. Flexibility also refers to the ability of the network to easily increase the variety of real-time services that it offers. It is our contention that availability and flexibility can be enhanced in a network by providing the network with the ...

Networking software is a growing bottleneck in modern workstations, particularly for high throughput applications such as networked digital video. We measure various components of the UDP/IP protocol stack in a DECstation 5000/200 running Ultrix 4.2a, and find that checksumming and copying dominate the processing time for high throughput applications. This paper describes network software measurements and performance improvements which derive from a faster checksum implementation.

This paper explores the problems associated with the multicasting of continuous media to support multimedia group applications. The interaction between multicasting and the delivery of multiple time-correlated continuousmedia streams with real-time delay requirements poses various new and interesting problems in research on communication protocols and architectures. We describe these problems, and identify where the opportunities are for effective solutions, all in the context of providing an overview of the current state of research in multimedia multicasting. The issues we discuss include quality of service, resource reservations, routing, error and traffic control, heterogeneity, and the use of hierarchical coding and open-loop control techniques.

Integrated-services networks will provide the communication infrastructure in the future. Unlike traditional communication networks, which are designed to offer a single type of service, integrated-services networks will offer multiple services, including data, voice, video, and others. Supporting applications with diverse traffic characteristics and performance objectives requires the offered services to be both flexible and guaranteed. To be flexible, integrated-services networks will use packet-switching technology. To provide performance guarantees in terms of throughput, delay, delay jitter, and loss rate, a proactive network control approach is needed. One of the most important components in this architecture is the service discipline at the switching nodes...

Hierarchical coding techniques split signals into components of varying importance. The aggregation of these components reconstructs the original data, but subsets of them can also provide various degrees of approximation to the original signal. Hierarchical coding is very important for the efficient use of high-speed packet-switching networks. The main issue for such network architectures is the significant congestion control problems that can arise due to the statistical multiplexing of many very high burstiness signals. A key property of any congestion control approach, which is not based on resource reservation at the peak rate of the sources, is the ability to shed load quickly without causing an avalanche of retransmissions of dropped traffic. With hierarchical coding of continuous media, when network congestion arises it is possible to drop the less important signal components without causing service interruption, and without the need for retransmissions. Since it is expected th...

At the Computer Systems Laboratory at UCSD, we conduct research in operating systems, communication networks, and performance evaluation. This document reviews the current research within the Computer Systems Laboratory. The final section contains descriptions of research projects undertaken by our students. For more information, contact the authors at the above address, or by FAX at (619) 534-7029. Joseph Pasquale may be contacted by e-mail at pasquale@ucsd.edu or by telephone at (619) 534-2673. George Polyzos may be contacted by e-mail at polyzos@ucsd.eduor by telephone at (619) 534-3508. 1 1 Introduction At the UCSD Computer Systems Laboratory (CSL), we conduct research in operating systems, communication networks, and performance evaluation. In operating systems, we are focusing on high performance I/O software support for a variety of I/O intensive applications, such as multimedia applications and scientific applications. In communication networks, we concentrate on problems a...

Emerging distributed multimedia applications have stringent performance requirements in terms of bandwidth, delay, delay-jitter, and loss rate. TheTenet real-time protocol suite provides the services andmechanismsfor delivering such performance guarantees, even during periods of high network load and congestion. The protocols achieve this by using resource management, connection admission control, and appropriate packet service disciplines inside the network. The Sequoia 2000 network employs the Tenet Protocol Suite at each of its hosts and routers making it one of the first wide area packet-switchednetworks to provide end-to-end per-connection performance guarantees. This paper presents experiments of the Tenet protocols on the Sequoia 2000 network including measurements of the performance of the protocols, the service received by real multimedia applications using the protocols, and comparisons with the service received by applications that use the Internet protocols (UDP/IP). We conclude that the Tenet protocols successfully protect the real-time channels from other traffic in the network, including other real-time channels, and continue to meet the performance guarantees, even when the network is highly loaded.