Quality of service in distributed multimedia systems

The Unix operating system made a vital contribution to information technology by introducing the notion of composing complicated applications out of simple ones by means of pipes and shell scripts. One day, this will also be possible with multimedia applications. Before this can happen, however, operating systems must support multimedia in as general a way as Unix now supports ordinary applications. Particularly, attention must be paid to allowing the operating-system service to degrade gracefully under heavy loads.\ud This paper presents the Quality-of-Service architecture of the Huygens project. This architecture provides the mechanisms that allow applications to adapt the level of their service to the resources the operating system can make available

Real Time in Plan 9

We describe our experience with the implementation and use of a hard-real-time scheduler for use in Plan 9 as an embedded operating system

Combining high performance and fault tolerance in a distributed file server

Among the most reliable and fault tolerant components in a distributed system are storage systems. Obviously, reliability of storage systems belongs to the most researched issues in distributed computing. Every distributed file system project is based on different assumptions about size, load, amount of sharing, and desirable semantics, making it hard to compare research results fairly. The current Amoeba file server is the Bullet File Server [van Renesse, Tanenbaum, and Wilschut, 1989] which provides immutable files, is optimized for whole-file transfer and does caching at the file server. It has excellent performance for reading cached files (1.5 + 1.5 n ms for n kilobytes) and for sustained file I/O (680 kilobytes per second, both on read and write). Although performance is excellent, there is room for improvement, especially in the area of fault tolerance, sharing semantics and caching. I am currently doing the back-of-the-envelope design for a new file server that will form the basis of both our normal file system and of a complex-object server which is being designed by the database group at CWI. In addition to those desirable properties of fault tolerance, persistency, consistency, and availability, I am anxious to achieve even better performance than the Bullet server by extensive use of client and server caching.This position paper presents some of our design ideas. Note that this is work in progress; that

Distributed systems management in wide area networks

While quite a few distributed operating systems for local-area networks exist, hardly any work has been done to date on distributed operating systems for wide-area networks. In Europe, a number of public networks are now operational, with gateways between some of them. However, the use of these networks is still mostly restricted to "remote login" and, in some cases, simple file transfer operations. To study these problems and to find structural solutions for efficient and simple use of national and international networks the working group "Distributed Systems Management" was founded within COST 11. Recently, this working group has submitted a research proposal to COST 11 to realise an infrastructure for the implementation of distributed services in a wide-area network in a European collaborative effort. The model, underlying the reserach is the service model, used in many local-area network distributed operating systems. The research project is described, and the proposed infrastructure is discussed in some detail

Protection and Resource Control in Distributed Operating Systems

Local networks often consist of a cable snaking through a building with sockets in each room into which users can plug their personal computers. Using such a network for building a coherent distributed or network operating system is difficult because the system administrators have no control over the user's machine ¿ not the applications programs, not the system kernel, not even the choice of hardware. In this paper we discuss a general method to protect such systems against malicious users without placing any restrictions on the kinds of operating systems that can be constructed. Depending on the details of the hardware, either one-way functions or public key cryptography forms the basis for the protection. As an example of our method, we show how a traditional object-oriented capability system can be implemented on top of the basic protection mechanism, and how a service for accounting and resource control can be constructed