Computer Networks and ISDN Systems 25 (1993) 719-721 719 North-Holland

Guest editorial

On tools for FDTs

J u a n Q u e m a d a

Departamento de Ingenieria Telematica, Ciudad Universitaria, ETSI Telecomunicacion, 28040 Madrid, Spain

Standards play a key role in communication sys- tems, where many systems have to interact and to communicate following a common set of rules which are usually known as protocols. The inter- pretation problems created by textual specifica- tions has led to the definition of Formal Descrip- tion Techniques (FDTs) with the purpose of us- ing them as the basic notation for describing non-ambiguous service and protocol standards. The particular engineering discipline which has appeared associated to FDTs started at the end of the seventies and has been called protocol engineering by some authors [5,4]. Protocol engi- neering is still a young discipline where FDTs with their associated tools and methodologies are slowly maturing.

Three FDTs have reached the status of inter- national standard. The oldest one is SDL [1] which was standardized by the CCIqq" in 1976. Several versions have followed in each series of colored books published by CCITT every four years. The Estelle [2] and LOTOS [3] standards were issued by ISO in 1988. SDL and Estelle are Extended Finite State Machine description lan- guages, whereas LOTOS is a temporal event or- dering description language. This special issue deals mainly with standardized FDTs. Other non standardized FDTs exist.

Formal descriptions of services and protocols are the central and unique references which should be used for the whole protocol engineer- ing process in which five different types of design tasks can be identified: 1. Realization and presentation of formal specifi-

cations;

2. Validation and verification; 3. Performance evaluation; 4. Implementation derivation; 5. Conformance testing.

A formal communication standard should be an implementation independent reference which can be validated, verified and analyzed in its abstract form, but which can be used also to generate and validate products which adhere to the standard. The existence of a unique and precise reference must guarantee the consistency of the chain of design tasks.

The first three tasks aim at producing a proper standard. The first task will produce the non-am- biguous standard, the second task will validate and verify its correctness and, the third task will determine that it has the proper performance.

The last two tasks aim at products which fol- low the standard. The fourth task will produce products which implement the standard, whereas the fifth task will provide a decision procedure in order to assess the conformance of a product to a given standard.

The existence of proper tools which automate a large part of the engineering procedures is essential in order to provide effective support by a given FDT to any of these design tasks and their availability will be one of the deciding fac- tors when choosing a given FDT for a realistic design. The goal of this special issue is, therefore, to provide a current view of existing tools for the most relevant FDTs and of current research ac- tivities in this area.

The accepted papers have been ordered ac- cording to the relation of the individual tools with

0169-7552/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved

720 J. Quemada / Guest editorial

the design tasks described above. Examples of tools supporting all design activities have been included except for conformance-testing-related tools.

There are no papers dealing with SDL; but, as his underlying model is a net of loosely coupled EFSMs as in Estelle, the examples of the latter can be considered as representing EFSM-based languages in general.

The issue starts with the paper written by Sam Chanson, Antonio Loureiro and Son Vuong which is entitled On tools supporting the use of formal description techniques in protocol development. This paper is written for readers interested in getting an overview of existing FDT tools. It contains a large survey of existing tools support- ing the standardized FDTs: Estelle, LOTOS and SDL. The paper analyzes the support of the existing tools to the particular design tasks.

The second paper, Protocol visualization in Estelle, is written by Paul Amer and Darren New. A tool for visualizing protocols specified in Es- telle, called GROPE, is presented. It exemplifies the graphical representation of networks of EFSMs connected through FIFO message queues and supports zooming, abstraction and animation capabilities.

The issue continues with a paper entitled An action-based framework for verifying logical and behavioural properties of concurrent systems which is written by Rocco De Nicola, Alessandro Fan- techi, Stefania Gnesi and Gioia Ristori. The pa- per describes a tool which illustrates the state of the art in verification of process algebra specifica- tions. The tool integrates other existing tools like AUTO or EMC and supports model checking of ACTL logic formula which are able to express properties dealing with notions such as necessity, possibility or eventuality. Only basic LOTOS ex- pressions are supported.

The fourth paper, VESAR: a pragmatic ap- oroach to formal specification and verification is

written by Bernard Algayres, Veronique Coelho, Laurent Doldi, Hubert Garavel, Yves Lejeune and Carlos Rodriguez. It can be considered as an illustration of verification tools for finite state models. The described tool, VESAR, provides verification of Estelle specifications by interac- tive, random or exhaustive reachability analysis where the exploration can be guided by observer processes.

The next paper, A LOTOS based performance evaluation tool, written by Carlos Miguel, Angel Fernfindez, Jose Manuel Ortufio and Le6n Vi- daller opens the topic of performance evaluation. It describes the TOPOSIM tool which accepts specifications written in a timed-probabilistic ex- tension of LOTOS called LOTOS-TP and per- mits the realization of performance evaluations of a LOTOS specification enriched with time-prob- abilistic information.

The sixth paper, Tool support to implement LOTOS formal specifications, is written by Jose Antonio Mafias, Tom~s de Miguel, Joaquln Sal- vachfa and Arturo Azcorra. An implementation environment based on the TOPO full LOTOS compiler is described which is able to generate standard C or ADA implementations. The imple- mentation approach is based on an annotations mechanism which permits the enrichment of LOTOS specifications with implementation de- pendent information. The paper describes the tool and the rational of the implementation ap- proach chosen.

A second paper on implementation is written by Rachid Sijelmassi and Brett Strausser and is entitled The PET and DINGO tools for deriving distributed implementations from EsteUe. It de- scribes an Estelle to C+ + distributed implemen- tation environment, based on the PET and DINGO compiler. PET translates Estelle into some kind of generic objects used as an interme- diate representation of Estelle specifications. DINGO provides a user guided translation of

Juan Quemada received a Telecommunication Engineering Degree in 1976 and a PhD in 1982 from the Technical University of Madrid (UPM). He taught at the Faculty of Informatics of UPM from 1977 till 1981. He joined the Telecommunications Engineering Highschool in 1982 where he is at present full professor in the Department of Telematic Engineering (DIT). His main areas of work during the last few years and his present research interests are protocols, communication architectures, formal methods and software engineering. He has been heavily involved in the development and application of LOTOS.

J. Quemada / Guest editorial 721

generic object definitions into a distributed Es- telle implementation which makes use of UNIX inter-process communication mechanisms.

The eighth paper entitled LOEWE: a LOTOS engineering workbench is written by Giinter Kar- joth, Carl Binding and Jan Gustafsson and opens the topic of integrated FDT environments. It describes LOEWE which is an example of an industrial integrated LOTOS design environment supporting simulation, verification and compila- tion. Although the individual topics are covered with less depth than in the previous papers, the integration aspects provide a new point of view.

Finally, the paper written by Gert Veltink and entitled The PSF toolkit describes another inte- grated FDT environment but for a different lan- guage called PSF. The PSF language is based on the ACP process algebra and can be used for specifying concurrent algorithms. The PSF toolkit provides simulation and verification capabilities.

References

[1] Sixth Plenary Assembly CCITT, ed., Orange Books, Vol. VIII.2, Chapter SDL--Specification and Description Lan- guage, CCITT, 1976.

[2] ISO IS 9074, Estelle--A Formal Description Technique Based on an Extended State Transition Model, ISO/TC97/SC21, 1988.

[3] ISO IS 8807, LOTOS--A Formal Description Technique Based on the Temporal Ordering of Observational Be- haviour, ISO/TC97/SC21, 1988.

[4] T. Piatkowski, Finite-state architecture, Technical Report, Systems Development Division, Research Triangle Park, NC, August 1975.

[5] H. Rudin, Protocol engineering: a critical assessment, in: S. Aggarwal and K. Sabnani, eds., Protocol Specification, Testing, and Verification, VIII, Proc. IFIP WG6.1 8th In- ternational Symposium, Atlantic City, NJ, USA, 7-10 June 1988 (North-Holland, Amsterdam, 1988) 3-16.