26441223
A Train Set as a Case Study for the Requirements Analysis of Safety-Critical Systems
64595679
Efficient LR(1) Parsers
21451715
Reliable Software: A Selective Annotated Bibliography
A total of 64 references to papers, books and conference proceedings on the subject of software reliability have been selected. Each of these references is provided with an annotation consisting of a paragraph of commentary. Sections of the bibliography are devoted to requirements definition, programming methodology, certification, fault-tolerance and reliability modelling.
298943
Error recovery for a boiler system with OTS PID controller
We have previously presented initial results of a case study which illustrated an approach to engineering protective wrappers as a means of detecting errors or unwanted behaviour in systems employing an OTS (off-the-shelf) item. The case study used a Simulink model of a steam boiler system together with an OTS PID (proportional, integral and derivative) controller. The protective wrappers are developed for the model of the system in such a way that they allow detection and tolerance of typical errors caused by unavailability of signals, violations of range limitations, and oscillations. In this paper, we extend the case study to demonstrate how forward error recovery based on exception handling can be systematically incorporated at the level of the protective wrappers.
15737185
Software Fault Tolerance: An Evaluation
In order to assess the effectiveness of software fault tolerance techniques for enhancing the reliability of practical systems, a major experimental project has been conducted at the University of Newcastle upon Tyne. Techniques were developed for, and applied to, a realistic implementation of a real-time system (a naval command and control system). Reliability data were collected by operating this system in a simulated tactical environment for a variety of action scenarios. This paper provides an overview of the project and presents the results of three phases of experimentation. An analysis of these results shows that use of the software fault tolerance approach yielded a substantial improvement in the reliability of the command and control system.
21069
Analyzing Safety Requirements for Process-Control Systems
Safety-requirements analysis is typically conducted either ad hoc or with the unbridled use of formal methods. The approach presented in this paper offers the freedom to mix formal and traditional engineering methods and apply them at different abstraction levels to give a higher assurance that the software's contribution to system risk is acceptable. >
14425373
On the stability of adaptive routing in the presence of congestion control
Efficient use of network resources has long been an important problem for large-scale network operators. To this end, several recent research efforts have proposed automated methods for optimizing routes based on traffic measurements. However, these efforts have not considered the stability of the dual feedback control mechanisms of adaptive routing and congestion control, when operating together. In this paper, we demonstrate that an important class of adaptive routing algorithms can yield stable optimal routes in the presence of congestion control, provided that either the congestion control mechanism is fair or the network workload behaves under reasonable constraints. We further show that one or the other of these assumptions is necessary for this class of adaptive routing algorithms -otherwise, unstable, sub-optimal routes may result in some pathological cases.
208003557
Serverless network file systems
We propose a new paradigm for network file system design: serverless network file systems. While traditional network file systems rely on a central server machine, a serverless system utilizes workstations cooperating as peers to provide all file system services. Any machine in the system can store, cache, or control any block of data. Our approach uses this location independence, in combination with fast local area networks, to provide better performance and scalability than traditional file systems. Furthermore, because any machine in the system can assume the responsibilities of a failed component, our serverless design also provides high availability via redundatn data storage. To demonstrate our approach, we have implemented a prototype serverless network file system called xFS. Preliminary performance measurements suggest that our architecture achieves its goal of scalability. For instance, in a 32-node xFS system with 32 active clients, each client receives nearly as much read or write throughput as it would see if it were the only active client.
2888831
The end-to-end effects of Internet path selection
The path taken by a packet traveling across the Internet depends on a large number of factors, including routing protocols and per-network routing policies. The impact of these factors on the end-to-end performance experienced by users is poorly understood. In this paper, we conduct a measurement-based study comparing the performance seen using the "default" path taken in the Internet with the potential performance available using some alternate path. Our study uses five distinct datasets containing measurements of "path quality", such as round-trip time, loss rate, and bandwidth, taken between pairs of geographically diverse Internet hosts. We construct the set of potential alternate paths by composing these measurements to form new synthetic paths. We find that in 30-80% of the cases, there is an alternate path with significantly superior quality. We argue that the overall result is robust and we explore two hypotheses for explaining it.
765629
A Comparison of File System Workloads
In this paper, we describe the collection and analysis of file system traces from a variety of different environments, including both UNIX and NT systems, clients and servers, and instructional and production systems. Our goal is to understand how modern workloads affect the ability of file systems to provide high performance to users. Because of the increasing gap between processor speed and disk latency, file system performance is largely determined by its disk behavior. Therefore we primarily focus on the disk I/O aspects of the traces. We find that more processes access files via the memory-map interface than through the read interface. However, because many processes memory-map a small set of files, these files are likely to be cached. We also find that file access has a bimodal distribution pattern: some files are written repeatedly without being read; other files are almost exclusively read. We develop a new metric for measuring file lifetime that accounts for files that are never deleted. Using this metric, we find that the average block lifetime for some workloads is significantly longer than the 30-second write delay used by many file systems. However, all workloads show lifetime locality: the same files tend to be overwritten multiple times.
1537776
Execution characteristics of desktop applications on Windows NT
This paper examines the performance of desktop applications running on the Microsoft Windows NT operating system on Intel x86 processors, and contrasts these applications to the programs in the integer SPEC95 benchmark suite. We present measurements of basic instruction set and program characteristics, and detailed simulation results of the way these programs use the memory system and processor branch architecture. We show that the desktop applications have similar characteristics to the integer SPEC95 benchmarks for many of these metrics. However, compared to the integer SPEC95 applications, desktop applications have larger instruction working sets, execute instructions in a greater number of unique functions, cross DLL boundaries frequently, and execute a greater number of indirect calls.