The reliability of a real-time digital control computer depends not only on the reliability of the hardware and software used, but also on the time delay in computing the control output, because of the negative effect...
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The reliability of a real-time digital control computer depends not only on the reliability of the hardware and software used, but also on the time delay in computing the control output, because of the negative effects of computing time delay on control system performance. For a given fixed sampling interval, the effects of computing time delay are classified into the delay and loss problems, The delay problem, occurs when the computing time delay is nonzero but smaller than the sampling interval, while the loss problem occurs when the computing time delay is greater than, or equal to, the sampling interval, i,e., loss of the control output, These two problems are analyzed as a means of evaluating real-time control systems, First, a generic analysis of the effects of computing time delay is presented along with necessary conditions for system stability, Then, we present both qualitative and quantitative analyses of the computing time delay effects on a robot control system, deriving upper bounds of the computing time delay with respect to system stability and system performance.
Ensuring that a distributed system with strict dependability constraints meets its prescribed specification is a growing challenge that confronts software developers and system engineers. This paper presents a techniq...
Ensuring that a distributed system with strict dependability constraints meets its prescribed specification is a growing challenge that confronts software developers and system engineers. This paper presents a technique for probing and fault injection of fault-tolerant distributed protocols. The proposed technique, called script-driven probing and fault injection, can be used for studying the behaviour of distributed systems and for detecting design and implementation errors of fault-tolerant protocols. The focus of this work is on fault injection techniques that can be used to demonstrate three aspects of a target protocol: detection of design or implementation errors;identification of violations of protocol specifications;and insight into design decisions made by the implementers. The emphasis of our approach is on experimental techniques intended to identify specific ''problems'' in a protocol or its implementation rather than the evaluation of system dependability through statistical metrics such as fault coverage. To demonstrate the capabilities of this technique, the paper describes a probing and fault injection toot, called the PFI tool (probe/fault injection tool), and a summary of several extensive experiments that studied the behaviour of two protocols: the Transmission Control Protocol (TCP) and a group membership protocol (GMP).
Ensuring that a system meets its prescribed specification is a growing challenge that confronts software developers and system engineers. Meeting this challenge is particularly important for distributed systems with s...
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ISBN:
(纸本)3540600426
Ensuring that a system meets its prescribed specification is a growing challenge that confronts software developers and system engineers. Meeting this challenge is particularly important for distributed systems with strict dependability and timeliness constraints. This paper presents a technique, called script-driven probing and fault injection, for the evaluation and validation of dependable protocols. The proposed approach can be used to demonstrate three aspects of a target protocol: i) detection of design or implementation errors, ii) identification of violations of protocol specifications, and iii) insight into design decisions made by the implementers. To demonstrate the capabilities of this technique, the paper briefly describes a probing and fault injection tool called the PFI tool, and several experiments on two protocols: the Transmission Control Protocol (TCP) [4, 24] and the Group Membership Protocol (GMP) [19]. The tool can be used to delay, drop, reorder, duplicate, and modify messages. It can also introduce new messages into the system to probe participants. In the case of TCP, we used the PFI tool to duplicate the experiments reported in [7] on several TCP implementations without access to the vendors' TCP source code in a very short time. We also ran several new experiments that are difficult to perform using past approaches based on packet monitoring and filtering. In the case of GMP, we used the tool to test the fault-tolerance capabilities of an implementation under various failure models including daemon/link crash, send/receive omissions, and timing failures. Furthermore, by selective reordering of messages and spontaneous transmission of new messages, we were able to guide a distributed computation into hard to reach global states without instrumenting the protocol implementation.
This paper presents pp-mess-sim, an object-oriented discrete-event simulation environment for evaluating multicomputer networks. The simulator provides a toolboz of various network topologies, communication workloads,...
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Scheduling messages on the controller area network (CAN) corresponds to assigning identifiers (IDs) to messages according to their priorities. If fixed priority scheduling such as deadline monotonic (DM) is used to ca...
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The switching scheme of a point-to-point network determines how packets flow through each node, and is a primary element in determining the network's performance. In this paper, we present and evaluate a new switc...
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The switching scheme of a point-to-point network determines how packets flow through each node, and is a primary element in determining the network's performance. In this paper, we present and evaluate a new switching scheme called hybrid switching. Hybrid switching dynamically combines both virtual cut-through and wormhole switching to provide higher achievable throughput than wormhole alone, while significantly reducing the buffer space required at intermediate nodes when compared to virtual cut-through. This scheme is motivated by a comparison of virtual cut-through and wormhole switching through cycle-level simulations, and then evaluated using the same methods. To show the feasibility of hybrid switching, as well as to provide a common base for simulating and implementing a variety of switching schemes, we have designed SPIDER, a communication adapter built around a custom ASIC, the Programmable Routing Controller (PRC).
Ensuring that a distributed system with strict dependability constraints meets its prescribed specification is a growing challenge that confronts software developers and system engineers. This paper presents a techniq...
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Ensuring that a distributed system with strict dependability constraints meets its prescribed specification is a growing challenge that confronts software developers and system engineers. This paper presents a technique for probing and fault injection of fault-tolerant distributed protocols. The proposed technique, called script-driven probing and fault injection, can be used for studying the behavior of distributed systems and for detecting design and implementation errors of fault-tolerant protocols. The focus of this work is on fault injection techniques that can be used to demonstrate three aspects of a target protocol: i) detection of design or implementation errors, ii) identification of violations of protocol specifications, and iii) insight into design decisions made by the implementers. The emphasis of our approach is on experimental techniques intended to identify specific "problems" in a protocol or its implementation rather than the evaluation of system dependability through statistical metrics such as fault coverage. To demonstrate the capabilities of this technique, the paper describes a probing and fault injection tool, called the PFI tool (Probe/Fault Injection Tool), and a summary of several extensive experiments that studied the behavior of two protocols: the transmission control protocol (TCP) and a group membership protocol (GMP).
Ensuring that a distributed real-time system with strict dependability constraints meets its prescribed specification is a growing challenge that confronts software developers and system engineers. This paper reports ...
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Ensuring that a distributed real-time system with strict dependability constraints meets its prescribed specification is a growing challenge that confronts software developers and system engineers. This paper reports on a software fault injection tool, called SockPFI, for testing the fault tolerance and timing behavior of distributed real-time applications. SockPFI, developed on Real-Time Mach, can be used to test socket-based distributed real-time applications on this platform without modifying the source code of the target protocol. The SockPFI tool is based on the concept of script-driven probing and fault injection. It is explicitly designed to address some of the intrusiveness associated with fault injection of distributed systems, and in particular, with real-time protocols. The paper describes the design and implementation of SockPFI on Real Time Mach, and a demonstration of the tool on a real-time primary-backup replication protocol.
It is difficult to define and evaluate a meaningful performance metric when many packets are generated and exchanged concurrently in mesh-connected multicomputers equipped with wormhole switching and virtual channels....
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It is difficult to define and evaluate a meaningful performance metric when many packets are generated and exchanged concurrently in mesh-connected multicomputers equipped with wormhole switching and virtual channels. Thus, an approximate metric/cost function must be chosen so that when, task modules are mapped by optimizing this function, the actual performance of the mapping is also optimized. Several low-complexity cost functions are evaluated using the simulated annealing optimization process. The mappings found by optimizing these cost functions are then fed into a flit-level simulator to evaluate their actual performance. One particular cost function is found to be very effective.
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