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Formal specification in OSI

  • Specification, Implementation And Conformance Of Protocols
  • Chapter
  • First Online:
Networking in Open Systems

Part of the book series: Lecture Notes in Computer Science ((LNCS,volume 248))

Abstract

Formal Description Techniques (FDTs) that should be capable to express the OSI Protocols and Services are confronted with unprecedented requirements in terms of the abstraction level at which the OSI architectural concepts need to be expressed as well as the high complexity of the OSI standards.

The development of the ISO FDTs Estelle and LOTOS for the formal specification of OSI standards has been accompanied and guided by a long period of extensive trial specifications. These exercises proved highly necessary to introduce and justify several FDT concepts and to test the appropriateness and expressive power of these FDTs for the intended application area.

The OSI requirements for FDT can be roughly divided into a category related to implementation independent specification and a category related to the structuring of complex specifications to achieve conciseness and readability.

Requirements that fall into the first category are related to architectural concepts like service access points, service primitives, connection identification mechanisms, implementation options, and non-deterministic operations of the protocol. It appears that the exercises in formal description did not only lead to better FDT concepts, but at the same time led to better insights into basic architectural concepts that underly OSI protocols and services.

The complexity of specifications can be coped with by the introduction of suitable structuring facilities such as composition operators, parameterization and recursion.

The language features of the FDTs must be based on a consistent semantical model. The FDTs Estelle and LOTOS have exploited quite different but complementary semantical models to tackle the architectural problems out of the application area.

This paper presents a few small, but significant, examples of fundamental architectural specification problems and discusses the different ways in which one may deal with them in LOTOS and in Estelle.

It is concluded that a few differences in elementary choices for the semantical model of the FDT, reflecting differences in interpretation and representation of basic architectural concepts, lead to vast differences in appearance of formal specifications. Some implications on current standardization work are outlined.

(On leave from University of Catania, Istituto di Informatica e Telecomunicazioni)

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Authors and Affiliations

  1. Dept. Informatics, Twente University of Technology, 7500 AE, Enschede, NL

    Chris A. Vissers & Giuseppe Scollo

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  1. Chris A. Vissers
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  2. Giuseppe Scollo
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Günter Müller Robert P. Blanc

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© 1987 Springer-Verlag Berlin Heidelberg

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Vissers, C.A., Scollo, G. (1987). Formal specification in OSI. In: Müller, G., Blanc, R.P. (eds) Networking in Open Systems. Lecture Notes in Computer Science, vol 248. Springer, Berlin, Heidelberg. https://doi.org/10.1007/BFb0026970

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  • DOI: https://doi.org/10.1007/BFb0026970

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  • Print ISBN: 978-3-540-17707-4

  • Online ISBN: 978-3-540-47777-8

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