The PROFIBUS formal specification: a comparison between two FDTs
Introduction
This paper describes and compares two formal specifications of Fieldbus Data Link (FDL) level and Fieldbus MAnagement (FMA1/2) services management of the PROcess FIeld BUS (PROFIBUS), using Specification Description Language (SDL) and Language Temporary Of Ordering Specification (LOTOS) as formal description languages. This work begins with a brief presentation of both Formal Description Techniques (FDTs) and how to use them in a system description. A brief introduction to the PROFIBUS protocol is then presented.
Two specifications are analysed from three points of view: protocol description, verification (simulation, validation and test generation) and implementation. The experience gained in this work allowed us to perform a comparison of both techniques in some phases of the formal specification. The comparison results and the conclusions are presented at the end of this paper.
Section snippets
SDL language introduction
SDL [9] is a standardized language used to specify and describe systems. It was developed by the ITU-T (International Telecommunications Union), former CCITT (Comité Consultatif International Telégraphique et Teléfonique), and published as the Z.100 ITU-T Recommendation. The development of the SDL began in 1972 as a research effort to find a notation to describe complex systems without ambiguities. The first version was published in 1976. Since then it has been improved with successive
LOTOS language introduction
LOTOS is an FDT [8] standardized by ISO (International Standardization Organization), to design services and protocols used in the communications of open systems OSI (Open Systems Interconnection).
Profibus description
In 1987 a group of manufacturers and end users, together with the German Government, defined a fieldbus [15] based on the OSI/ISO model named PROFIBUS. This description was later published as the German standard DIN 19 245 [21] and as the European CENELEC IN 50170 [3]. PROFIBUS only uses three layers of the OSI model: the physical layer PHY, the data link layer FDL and the application layer FMS/LLI (Fieldbus Message Specification/Lower Layer Interface). Furthermore it includes a group of
Formal description of PROFIBUS
The PROFIBUS protocol specification has been gained after a deep analysis of the written standard (not formal). In this analysis some ambiguities and errors have been detected, most of them belonging to the states machine that describes the MAC layer operation, where some transitions between states are not very efficient from the automata theory point of view. Some solutions have been adopted to solve these ambiguities.
In both specifications, LOTOS and SDL, the main entities that conform the
Simulation, validation and test
The simulation, the validation and the implementation test of each specification has been performed following an appropriate methodology depending on each language capabilities and the available tools. Both works are explaining following, but before it is important to establish what is understood here with these three concepts:
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Simulation. It is a functional execution of the specification by using help tools.
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Validation. Its main goal is to probe the right behaviour of the specification.
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Test. To
Physical implementation
The formal specifications of a PROFIBUS station in both languages LOTOS and SDL have been physically implemented. They have been generated after their verification as it was described in the previous paragraphs. To get these implementations it was necessary to code some functions in C language, to communicate the formal specification with the hardware devices where they finally were executed. The formal specification code was generated by the LOLA and Telelogic TAU tools.
As is shown in Fig. 6,
Specifications comparison
The formal specification of a communications protocol so complex as PROFIBUS, requires a high command with the language and tools to be used. This knowledge is not acquired but with the practice in the description of complex systems, where all their functionality is required. It is here where the advantages or drawbacks of using one or another language becomes evident.
The aim of this comparison is not to conclude in favour of LOTOS or SDL like a formal description language. Apart from
Conclusions
The formal description of a PROFIBUS network contributes to the introduction of the FDTs in the specification of industrial communications protocols [15]. There have been found some ambiguities in the written standard (not formal) in natural language. Some of these ambiguities arise after a detailed reading of the standard text, and others have been shown during the formal specification. Therefore the formal specification process has allowed us to verify and to complete the written standard.
Acknowledgements
This work was made from two R&D projects sponsored by the following entities: R&D National Secretary And CICYT, Ref. DPI2000-1702, Central Government (Madrid, Spain) and Research Vicechancellorship, Ref. 64102I004, University of Vigo (Spain).
P. Mariño received his doctorate in Telecommunications Engineering from the Polytechnic University of Madrid (Spain 1984). He is a professor at the Electronic Technology Department (University of Vigo, Spain). He is a visiting scientist in the Computer Science Department of Carnegie Mellon University (Pittsburgh, USA 1988). He is an expert on Information Technology from the Commission of the European Communities for the SPRINT (Luxembourg 1991) and COPERNICUS (Brussels 1994) programs. He is the
References (26)
Formal methods for telecommunication system requirements: a survey of standardized languages
Annals of Software Engineering
(1997)- CENELEC EN 50170, General Purpose Field Communication System, vol. 2/3 (PROFIBUS), December...
- et al.
SDL: Formal Object-oriented Language for Communicating Systems
(1997) Seven myths of formal methods
IEEE Computer
(1990)- ISO/IS 7498, Basic Reference Model for Open Systems Interconnection,...
- ISO IS 9074, Information processing systems – Open Systems Interconnection: ESTELLE: A formal description technique...
- ISO IS 8807, Information processing systems – Open Systems Interconnection: LOTOS: A formal description technique based...
- ITU-T, Recommendation Z.100: Specification and Description Language SDL,...
- ITU-T, Recommendation Z.105: Use of SDL with ASN.1,...
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P. Mariño received his doctorate in Telecommunications Engineering from the Polytechnic University of Madrid (Spain 1984). He is a professor at the Electronic Technology Department (University of Vigo, Spain). He is a visiting scientist in the Computer Science Department of Carnegie Mellon University (Pittsburgh, USA 1988). He is an expert on Information Technology from the Commission of the European Communities for the SPRINT (Luxembourg 1991) and COPERNICUS (Brussels 1994) programs. He is the director of Digital Communications Division from the Applied Electronics Institute (University of Vigo, Spain). He is a member of IEEE. e-mail: [email protected]
J. Nogueira received his doctorate in Telecommunications Engineering from the University of Vigo, Spain in 2000. He is a full professor in the Electronic Technology Department (University of Vigo, Spain). He is also a researcher of Digital Communications Division from the Applied Electronics Institute (University of Vigo, Spain). e-mail: [email protected]
C. Sigüenza. Telecommunications Engineer from the University of Vigo. (Spain 1995). IT Design Manager in GOC, Quality Control Corporation (Vigo, Spain 1996–1998). IT Data Warehouse Consultant and Project Manager in a Mobile Telco Corporation (Madrid, Spain 1998–1999). PhD Researcher of Digital Communications Division from the Electronic Technology Department (University of Vigo, Spain).
P. Poza received his doctorate in Electronics Engineering from the University of Vigo, Spain in 1997. He is a full professor in the Electronic Technology Department (University of Vigo, Spain). He is also a researcher of Digital Communications Division from the Applied Electronics Institute (University of Vigo, Spain). e-mail: [email protected]
M. Domı́nguez received his doctorate in Telecommunications Engineering from the University of Vigo, Spain in 2000. He is a full professor in the Electronic Technology Department (University of Vigo, Spain). He is also a researcher of Digital Communications Division from the Applied Electronics Institute (University of Vigo, Spain). e-mail: [email protected]