Leistungsbewertung automatisch generierter Protokollimplementierungen mit Estelle

Formale Beschreibungstechniken (FDTs) erlauben durch ihre formale Syntax und Semantik eine präzise Systembeschreibung und sind Grundlage für die formale Verifikation. Bei der Implementierung von Systemen wird jedoch nach wie vor von Hand implementiert, selbst wenn ausgereifte Werkzeuge zur automatischen Generierung von Kode direkt aus der formalen Spezifikation existieren. Die Ursache dafür liegt in dem Ruf dieser Werkzeuge, Kode mit extrem geringer Leistungsfähigkeit zu erzeugen. Es gibt jedoch kaum quantitative Leistungsvergleiche zwischen manuell und automatisch generierten Implementierungen, die dieses Vorurteil stützen oder widerlegen könnten. In diesem Beitrag wird ein solcher Leistungsvergleich anhand des Hochleistungsprotokolls XTP und der FDT Estelle vorgestellt. Er liefert eine Bestandsaufnahme des momentanen Entwicklungsstandes bei der automatischen Generierung von Kode aus Estelle-Spezifikationen im direkten Vergleich zu gut optimierten Handimplementierungen. Es zeigt sich, daß in dem betrachteten Fall eines komplexen Protokolls die Handimplementierung zwar merklich leistungsstärker ist. Dieser Leistungsvorteil wird jedoch durch einen sehr hohen Implementierungsaufwand sowie die Schwierigkeit, die Korrektheit bzgl. der Spezifikation sicherzustellen, erkauft. Im einzelnen Anwendungsfall kann es daher trotz der Leistungseinbußen durchaus vorteilhaft sein, automatisch Kode zu erzeugen, zumal in der Bestandsaufnahme festgestellt wurde, daß automatisch generierte Implementierungen z.T. besser abschneiden als erwartet. Zudem besteht - anders als bei der bereits umfassend optimierten Handimplementierung - noch ein erhebliches ungenutztes Potential zur Leistungsverbesserung der automatisch generierten Implementierung

Multi-hop Clock Synchronization in Wireless Ad-Hoc Networks

In this paper, we introduce Black Burst Clock Synchronization (BBCS), a novel protocol for multi-hop time synchronization in wireless ad-hoc networks, located at MAC level. BBCS is based on the exchange of synchronized tick and time frames, which are protected against collisions by a special encoding using black bursts. It provides a deterministic upper bound for clock offset that only depends on maximum network diameter, and on the used transceiver hardware. BBCS has low complexity in terms of communication, computation, storage, structure, and energy consumption. It provides low and deterministic convergence delay, and is robust against node movements and node failures. In this work, we introduce BBCS, provide a formal analysis of its properties, and evaluate the required overhead for clock-synchronizing a multi-hop wireless ad-hoc network

A Clock-independent Model for Real-Time

A new approach for modelling time that does not rely on the concept of a clock is proposed. In order to establish a notion of time, system behaviour is represented as a joint progression of multiple threads of control, which satisfies a certain set of axioms. We show that the clock-independent time model is related to the well-known concept of a global clock and argue that both approaches establish the same notion of time

A Case Study on Specifikation,Detection and Resolution of IN Feature Interactions with Estelle

We present an approach for the treatment of Feature Interactions in Intelligent Networks. The approach is based on the formal description technique Estelle and consists of three steps. For the first step, a specification style supporting the integration of additional features into a basic service is introduced . As a result, feature integration is achieved by adding specification text, i.e . on a purely syntactical level. The second step is the detection of feature interactions resulting from the integration of additional features. A formal criterion is given that can be used for the automatic detection of a particular class of feature interactions. In the third step, previously detected feature interactions are resolved. An algorithm has been devised that allows the automatical incorporation of high-level design decisions into the formal specification. The presented approach is applied to the Basic Call Service and several supplementary interacting features

Decomposing Service Definition in Predicate/Transition-Nets for Designing Distributed Systems

In this paper, we propose a new algorithm for the derivation of a protocol specification in Pr/T-nets, which is the specification of communicating N entities (N can be given), from a given service specification in Pr/T-nets and an allocation of the places of the service specification to the N entities. Our algorithm decomposes each transition of the service specification into a set of communicating Pr/T-subnets running on the N entities. Moreover, for the efficient control of conflict of shared resources, we present a timestamp-based mutual exclusion algorithm and incorporate it into the derivation algorithm

On the Suitability of Estelle for Multimedia Systems

Formal Description Techniques have been widely used for the specification of traditional networked applications. They have not been applied to the specification of new applications such as multimedia systems yet. In this paper, we examine the FDT Estelle with respect to its suitability for multimedia system specification and automatic derivation of efficient implementations. We show that it is possible to specify certain aspects of multimedia systems, but that Estelle is not sufficient for others. The derived implementations often perform badly. We show the reasons and propose to use a slightly modified Estelle syntax and semantics to solve the problems. The implemented solution was tested successfully

Search for CP Violation in the Decay Z -> b (b bar) g

About three million hadronic decays of the Z collected by ALEPH in the years 1991-1994 are used to search for anomalous CP violation beyond the Standard Model in the decay Z -> b \bar{b} g. The study is performed by analyzing angular correlations between the two quarks and the gluon in three-jet events and by measuring the differential two-jet rate. No signal of CP violation is found. For the combinations of anomalous CP violating couplings, ${\hat{h}}_b = {\hat{h}}_{Ab}g_{Vb}-{\hat{h}}_{Vb}g_{Ab}$ and $h^{\ast}_b = \sqrt{\hat{h}_{Vb}^{2}+\hat{h}_{Ab}^{2}}$, limits of \hat{h}_b < 0.59$and$h^{\ast}_{b} < 3.02$ are given at 95\% CL.Comment: 8 pages, 1 postscript figure, uses here.sty, epsfig.st