P. Verssimo, A. Casimiro, and C. Fetzer. The timely computing base: Timely actions in the presence of uncertain timeliness. In Proceedings of the International Conference on Dependable Systems and Networks, pages 533--542, New York City, USA, June 2000. IEEE Computer Society Press.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....whose main objective is precisely to detect the failure of timeliness specifications. This is only possible because the TTCB is timely, i.e. the TTCB is a real time (synchronous) component. Many of the time related ideas and services of the TTCB were based on the work of the Timely Computing Base [23]. The protocol presented in this paper uses a single time service the Trusted Absolute Timestamping Service. This service provides globally meaningful timestamps. It is possible to obtain timestamps with this characteristic because local TTCBs clocks are synchronized. 2.3 Processes and ....

....is nothing wrong with this, since it allows progress of the protocol, but this method is subject to inconsistencies if failures are not detected correctly. In our system, we rely on the timing failure detector of the TTCB to ensure complete and accurate failure detection amongst all participants [23], and feed a membership service complementing the reliable multicast protocol being described. These mechanisms are out of the scope of the present paper, but substantiate the correctness of the omission degree technique for asynchronous environments. 3 Protocol Definition and Properties In each ....

P. Verssimo, A. Casimiro, and C. Fetzer. The Timely Computing Base: Timely actions in the presence of uncertain timeliness. In Proc. the International Conference on Dependable Systems and Networks, pages 533--542, June 2000.

.... distributed systems have been considering, as a basic building block [14] a group membership service, which precisely aims at emulating a Perfect failure detector, i.e. when a process is suspected, i.e. timed out, it is excluded from the group: every suspicion hence turns out to be accurate [4, 6, 16]. As a side e#ect of our work, we point out two interesting results in our general environment. First, if we consider the correct restricted variant of consensus (i.e. non uniform consensus) is clearly not the weakest. A simple corollary of this observation is that (uniform) consensus is ....

P. Verissimo, A. Casimiro and C. Fetzer. The Timely Computing Base: Timely Actions in the Presence of Uncertain Timeliness. Proceedings of the IEEE International Symposium on Dependable Systems and Networks (DSN), 2000.

....is seriously affected. This paper is concerned with the performance of group communication in systems where these sort of perturbations may occur without impact in correctness. Our approach is complementary to mechanisms that detect timing failures affecting correctness in real time systems [9, 27]. 2.2 Design Alternatives We can identify different alternative approaches to address the problems caused by the occurrence of transient performance perturbations and to avoid degradation of group throughput by flow control: Exclude a process from the group as soon as it suffers a performance ....

P. Verssimo, A. Casimiro, and C. Fetzer. The timely computing base: Timely actions in the presence of uncertain timeliness. In Proc. Intl. Conf. on Dependable Systems and Networks (DSN'00), pages 533--542, New York City, USA, June 2000. IEEE Computer Society Press.

....messages appropriately, we divide the system into parts and assure that at least one of them will be timely. In other words, our assumed model of computation can be considered synchronous but only with respect to the process that transmits the highest priority message. Other models of computation [14, 15] have assumed different levels of synchrony in different parts of the system. These models consider the system made of two distinct parts, one synchronous and the other semi synchronous. The synchronous part is used to control and adjust the semisynchronous one, where complete synchronism may not ....

P. Verssimo, A. Casimiro, and C. Fetzer. "The Timely Computing Base: Timely Actions in the Presence of Uncertain Timeliness". In Int'l Conf. on Dependable Systems and Networks (DSN 00), June 2000.

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P. Verssimo, A. Casimiro, and C. Fetzer, "The timely computing base: Timely actions in the presence of uncertain timeliness," in Proceedings of the International Conference on Dependable Systems and Networks, New York City, USA, June 2000, pp. 533--542.

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P. Verssimo, A. Casimiro, and C. Fetzer. The timely computing base: Timely actions in the presence of uncertain timeliness. In Proceedings of the International Conference on Dependable Systems and Networks, pages 533--542, New York City, USA, June 2000. IEEE Computer Society Press.

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P. Verssimo, A. Casimiro, and C. Fetzer. The timely computing base: Timely actions in the presence of uncertain timeliness. In Proceedings of the International Conference on Dependable Systems and Networks, pages 533--542, New York, USA, June 2000. IEEE Computer Society Press.

....by each protocol. this paper we show how to check the synchronous properties during run time and enforce the properties by failing a process before a property can actually be violated. Our protocol could be used to ensure the synchronous system properties of a timely computing base as proposed in [17]. The transformation of system model properties is not new. For example, Lamport and Lynch noted already in [13] that one can transform many properties of one model into properties of another model. Another way to view such transformation is, that one transforms a distributed algorithm tolerant ....

P. Verissimo, A. Casimiro, and C. Fetzer. The timely computing base: Timely actions in the presence of uncertain timeliness. In Proceedings of the International Conference on Dependable Systems and Networks, pages 533--542, New York,NY, June 2000. 16

....the remaining are related with its operational purpose. It concerns the balance between faults avoided (prevented or removed) and faults tolerated. On the one hand, this is concerned with the zero vulnerabilities goal taken in many classical security designs. The Trusted Computing Base paradigm[36], when postulating the existence of a computing nucleus that is impervious to hackers, relies on that assumption. Over the years, it became evident that this was a strategy impossible to follow in generic system design: systems are too complex for the whole design and configuration to be mastered. ....

Verssimo, P., Casimiro, A., Fetzer, C.: The Timely Computing Base: Timely actions in the presence of uncertain timeliness. In: Proceedings of the International Conference on Dependable Systems and Networks. (2000) 533--542

....a model of partial or uncertain synchrony, that can vary anywhere in the space between synchronous and asynchronous. The specific models that best reflect NAVTECH s synchrony assumptions are the timed asynchronous[12] and the quasi synchronous[46] models, or the recent timely computing base model[41]. 3.1 Topological Model NAVTECH was designed for large scale applications. Topology issues and communication system characteristics have a fundamental impact on the achievable scale of computations, 4 as systems grow in span, complexity and number of hosts. A large scale network such as the ....

....to be effective. More recently, it has been shown[17, 2] that if they could further detect timing failures in a timely manner, the system would be able to address timeliness problems, even if being almost asynchronous or imperfectly synchronous. Timed accuracy and completeness were defined in [41], allowing to characterize timing failure detectors. Usually, the output of failure detectors serves the purpose of system reconfiguration, for example, a progress condition of a protocol, a new view in the membership of a group. However, when: a) the criterion for a detector to declare crash of ....

P. Verssimo, A. Casimiro, and C. Fetzer. The timely computing base: Timely actions in the presence of uncertain timeliness. In Proceedings of DSN 2000.

....executing an operation, the TTCB can calculate an upper bound on the time taken to execute it (duration measurement service) and give feedback to the calling entity on how well it did with regard to time. This mechanism is inspired by the Timely Computing Base work, and explained with detail in [70]. 2.2.2 The TTCB Services The TTCB services can be roughly divided in security related services and timerelated services. The security related services were selected considering the TTCB design principles [69] and a set of informal criteria: The services should be the minimal set that ....

....absolute timestamping Provides globally meaningful timestamps. Figure 2.5: TTCB Services The TTCB services are summarized in Figure 2.5. The implementation of the security related services is presented in [27, 26] The design and implementation of the time related services can be found in [70, 19, 20]. The following subsections describe the TTCB services and their APIs. Figure 2.6 shows the meaning of some common API parameters. Parameter Description eid an entity identification before the TTCB elist a list of entities identified by their eids tag an unique id for an execution of a service ....

P. Verssimo, A. Casimiro, and C. Fetzer. The timely computing base: Timely actions in the presence of uncertain timeliness. In Proceedings of the International Conference on Dependable Systems and Networks, pages 533--542, June 2000.

....question is motivated by the uncertain timeliness properties of target infrastructures. If we don t know in which infrastructures applications will execute, how can we make assumptions about timing variables like for instance the network transmission delay. The Timely Computing Base model (TCB) [11, 12] proposes an architectural construct that constitutes a generic approach to the problem of programming applications with real time requirements in the presence of uncertain timeliness. The TCB model assumes the existence of a component, capable of executing timely functions, which helps ....

P. Verfssimo, A. Casimiro, and C. Fetzer. The timely computing base: Timely actions in the presence of uncertain timeliness. In Proceedings of DSN 2000.

....contrast, we address the above mentioned hard problems in the time domain under the light of partial synchrony models, which can withstand varying timeliness or synchrony conditions, and the occurrence of timing failures. Our approach follows recent work on timing and QoS failure detection oracles [41] under partial synchrony models that reason in terms of the assumption, coverage binomial. This may help provide a precise definition of predictability, in terms of an assurance to which a probability is attached, and thus provide conditions for objects to make justifiable tradeoffs between ....

P. Verissimo, A. Casimiro and C. Fetzer. The Timely Computing Base: Timely actions in the presence of uncertain timeliness. In Proceedings of the International Conference on Dependable Systems and Networks, pages 533-542, New York City, USA, June 2000. IEEE Computer Society Press.

.... [6] the quasi synchronous model, where some parts of the system have enough synchronism to perform real time actions with a certain probability [17] and the work on partial synchrony presented in [7, 8] All these papers have in fact motivated the idea behind the work on the TCB model [19]: the search of a generic paradigm for systems with uncertain temporal behavior. The significance of the TCB model in the context of factory environments is particularly important when the trend is to use low cost components, shared by many applications. Given the unpredictability of such an ....

....may also provide the required predictable behavior. 3 A Generic Model for Timely Computing Due to lack of space, this section only presents a brief overview of the Timely Computing Base model, its services and interfaces. A complete and detailed description of these issues appears in [18] and [19]. 3.1 The Timely Computing Base Model A system with a TCB is divided into two well defined parts: a payload and a control part. The generic or payload part prefigures what is normally the system in homogeneous architectures. It exists over a global network or payload channel and is where ....

[Article contains additional citation context not shown here]

P. Verssimo, A. Casimiro, and C. Fetzer. The Timely Computing Base: Timely actions in the presence of uncertain timeliness. In Proceedings of the International Conference on Dependable Systems and Networks (ICDSN'00),New York, USA, June 2000.

.... to design adaptive real time applications [16] The quasi synchronous model, developed by one of the present authors, assumes that parts of the system have enough synchronism to perform real time actions with a certain probability [26] These works were in general precursors of the TCB model [25], which provides a more generic framework to address asymmetries (both in space and time) of the system synchrony and is therefore adequate to handle a vast range of problems. 3 Timely Computing This section provides an overview of the Timely Computing Base model. Its properties and engineering ....

....and engineering principles are firstly described, followed by the basic services essential for timely and dependable computing. Lastly, we discuss the most relevant issues related to the application programming interface. A complete and detailed description of these issues appears in [27] and [25]. 3 3.1 The Timely Computing Base Model A system with a Timely Computing Base (TCB) is divided into two well defined parts: a payload and a control part. The generic or payload part prefigures what is normally the system in homogeneous architectures. It exists over a payload network and is ....

[Article contains additional citation context not shown here]

P. Verssimo, A. Casimiro, and C. Fetzer. The Timely Computing Base: Timely actions in the presence of uncertain timeliness. In Proceedings of the International Conference on Dependable Systems and Networks, pages 533--542, New York, USA, June 2000. IEEE Computer Society Press.

....timing failure detection. We are particularly interested in a model based on the existence of a timely computing base, which is both a timely execution assistant and a timing failure detection oracle that ensures time domain correctness of applications in environments of uncertain synchronism [7]. This research has focused on benign (non arbitrary, nonmalicious) failure models. However, the architectural characteristics of the timely computing base enable its extension in order to be resilient to value as well as time domain failures. We call such an extended model, whose development we ....

.... as major contributors IBM Zurich with the definition of some CS protocols [2] University of Newcastle upon Tyne who are extending their work on long running transactions [10] and University of Lisboa with the development of a secure group communication suite on the partially synchronous model [7]. Partners from DERA and University of Saarlandes are formally verifying and assessing some of the protocols that are being produced [5] ....

P. Verssimo, A. Casimiro, and C. Fetzer. The timely computing base: Timely actions in the presence of uncertain timeliness. In Proc. of the Int'l Conf. on Dependable Systems and Networks, June 2000.

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P. Verssimo, A. Casimiro, and C. Fetzer. The timely computing base: Timely actions in the presence of uncertain timeliness. In Proceedings of the International Conference on Dependable Systems and Networks, pages 533--542, New York City, USA, June 2000. IEEE Computer Society Press.

No context found.

P. Verssimo, A. Casimiro, and C. Fetzer, "The timely computing base: Timely actions in the presence of uncertain timeliness," in Proc. International Conference on Dependable Systems and Networks (FTCS-30/DCCA-8), pp. 533--542, 2000.

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P. Verssimo, A. Casimiro, and C. Fetzer. "The Timely Computing Base: Timely Actions in the Presence of Uncertain Timeliness". In Proc. of the Int'l Conference on Dependable Systems and Networks (DSN), pages 533--542. IEEE Computer Society Press, 2000.

No context found.

P. Verissimo, A. Casimiro, and C. Fetzer. The timely computing base: Timely actions in the presence of uncertain timeliness. In Proc. of the Int'l Conf. on Dependable Systems and Networks, pages 533--542, New York City, USA, june 2000. IEEE Computer Society Press.

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P. Verissimo, A. Casimiro, and C. Fetzer. The timely computing base: Timely actions in the presence of uncertain timeliness. In Proc. of the Int'l Conf. on Dependable Systems and Networks, pages 533--542, New York City, USA, june 2000. IEEE Computer Society Press.

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P. Verissimo, A. Casimiro, and C. Fetzer. The Timely computing base: Timely actions in the presence of uncertain timeliness. In Proceedings of the International Conference on Distributed Systems and Networks, pages 533--552, New York, USA, June 2000.

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P. Verissimo, A. Casimiro, and C. Fetzer. The timely computing base: Timely actions in the presence of uncertain timeliness. In Proc. of the Int'l Conf. on Dependable Systems and Networks, pages 533--542, New York City, USA, june 2000. IEEE Computer Society Press.

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P. Verssomo, A. Casimiro, and C. Fetzer, "The Timely Computing Base: Timely Actions in the Presence of Uncertain Timeliness," Proceedings of International Conference of Dependable Systems and Networks, pages 533-542, 2000.

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P. Verissimo, A. Casimiro, and C. Fetzer. The timely computing base: Timely actions in the presence of uncertain timeliness. In Proc. of the Int'l Conf. on Dependable Systems and Networks, pages 533--542, New York City, USA, june 2000. IEEE Computer Society Press. 10

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