standardization aspects

Ž .Computer Standards & Interfaces 19 1998 249–256

Standardization aspects

Robert Patzke a,), Harald Schumny b, Norbert Zisky b

a MFP, Theodor-Storm-Str. 3r3a, D-31515 Wunstorf, Germanyb ( )Physikalisch-Technische Bundesanstalt PTB , Furstenwalder Damm 388, D-12587 Berlin, Germany¨

Abstract

In principle, standard devices are designed to achieve rationalization effects by type standardization. Uniform compo-nents are at the basis of every series production. The high technical level in the industrialized countries is not conceivablewithout standardization. In contrast to the large number of de facto standards which follow as a natural result of the demandsof man and technology and which develop from the consistent use of good technical solutions, written standards are theresult of a deliberate unification by intellectual means. This path towards developing a standard device is followed wheneverit appears that a development will not take place on its own or when systems widely used are not appropriate for the

Ž . Žrespective area of application wrong standards . In order to point out main aspects, the example of EPSI European Petrol.Station Interface is used. q 1998 Published by Elsevier Science B.V. All rights reserved.

Keywords: Standardization; Interfaces; Fieldbuses; Users’ interests; Manufacturers’ interests; EPSI; MMS

1. What purpose does a technical standard serve?

Standardization activities are usually initiated bythe users, as they expect that standardization willallow them to gain independence from indiÕidualmanufacturers. Compared with widely used manu-

Ž .facturer-specific systems de facto standards , stan-dardization has the decisive advantage that the tech-nical characteristics are disclosed. Only in this waywill it, in fact, be possible to pass a clear and neutraljudgement on the suitability of a technique for aspecific purpose. In contrast to manufacturer-specific

) Corresponding author. Tel.: q49 5031 13790; fax: q49 503115687; e-mail: [email protected]

standards, written standards are not, however, dis-tributed by marketing methods. Their role is a pas-sive one, and actual application of the standards toproducts must all time and again be demanded by all

Ž .those interested buyers, users . This situationchanges when a written standard is widely appliedand has already produced clear rationalization ef-fects. A deviation from the standard will then causeconsiderable cost, and a product will no longer suc-ceed on the market in the case of non-compliancewith the established standard.

Ž .An absolutely essential advantage of a goodstandard is that the technical specifications take intoaccount not only the viewpoint of one or severalmanufacturers but also the users’ ideas. This usuallyleads to a clear simplification of the technique whichthus, is transparent to wide circles and controllable.

0920-5489r98r$ - see front matter q 1998 Published by Elsevier Science B.V. All rights reserved.Ž .PII: S0920-5489 98 00026-9

( )R. Patzke et al.rComputer Standards & Interfaces 19 1998 249–256250

Thus, application prevails over the technique. Thereverse is often true of manufacturer-specific sys-tems, where practical application is determined bythe technique used.

2. Typical development of a standard for deviceinterfaces

2.1. MotiÕes and fundamental standardization prob-lems

Measuring instruments which are part of com-puter-controlled systems are integrated through thedevice interface. The computer interface and thedevice interface must be compatible; computer anddevice become a unit through this connection. Theuser no longer purchases single instruments fromvarious manufacturers but buys the overall systemfrom one manufacturer. When individual compo-nents of the overall system no longer meet the user’squality requirements, he cannot replace them by thebetter products of a competitor. Only the overallsystem can be replaced. Basically, this also meansthe change of the manufacturer, with all conse-quences.

The manufacturer-specific device interface clearlycuts down the ‘fluctuation’ of devices incorporatedin systems. This entails ‘rigid’ manufacturerruser

Ž .relations dependence on manufacturer , which ulti-mately reduce the user’s influence on the quality andprice of individual devices or even make any influ-ence altogether impossible. The threat to buy fromthe competitors usually proves to be ineffective.

When all manufacturers use the same device in-terface, it will be possible to replace devices bychoosing from among the products offered by differ-ent manufacturers. To achieve this, it will not besufficient to define only the mechanical and electri-cal characteristics of the interface; the transmissionprotocols, as well as function and representation ofthe transmitted data are to be defined. The interna-tional reference model for an open system describedin ISO 7498 is the basis for an appropriate standard-ization. When the implications of the data contentsfor the device function are defined as well, devicesof the same type can, in fact, be replaced without thebehaviour of the overall system being affected. How-ever, only the users will benefit from such a standarddevice; the manufacturers must fear strong fluctua-tions in instrument purchases. From this follows aconflict between the users’ and manufacturers’ inter-ests, which will render standardization in this fieldextremely difficult.

A distinction between the viewpoints of user andmanufacturer must also be made when the technicaldetails are defined. For users, of course, applicationranks higher than the technique used, and their re-quirements are usually as described below. The ex-

Ž .ample EPSI European Petrol Station Interface willbe dealt with in Section 4.

The technique must EPSI characteristics-be suitable for the defined field -derived from conventional petrol station technique

Žof use for example, be based on.the present state of the art

Ž .-have provision for extension -theoretical reserve capacity compared with the 1993 field test )1000;Žsolution of today’s problems reserve at present achievable: about 60; reserve during field test: about

. Žwith sufficient reserve 10; in addition, very high flexibility of data coding structures of.variables

Ž-be reasonably priced simple -today’s know-how and the manufacturers’ technical aids are suitable fortechnique, no increase in the the development; only standard components commonly available are usedinstruments’ price, no extraexpenses for diagnosis and

.maintenance

( )R. Patzke et al.rComputer Standards & Interfaces 19 1998 249–256 251

The manufacturers’ demands on the technique to be used often goes beyond the above.

The technique Possible criticism of EPSI-is to be suitable for all applications -in the first place orientated to petrol stations

Žof the manufacturer tailored to the.whole range of products

-is to have provision for extension -by the users’ specifications at present limited to required functionsŽsuitable also for all future

.productsŽ-be reasonably priced entail a -for the time being only defined as software solution

minimum of development work;.chip, if possible

The users’ and manufacturers’ views are oppositealso with regard to the technical aspects. The usersrequire a simple technique, tailored to the respectiÕeproblem, in contrast to the manufacturers who favoura uniÕersal technique applicable to as wide a rangeas possible. It is obvious that above all, large manu-facturing firms wish that a great variety of technicalrequirements shall be met, which in the end willresult in a clear increase in the devices’ prices.

At the beginning of interface standardization we,therefore, find ourselves faced with the followingsituation:1. A difficult initial situation as regards market pol-

icy, due to opposed interests of manufacturers andusers.

2. Different demands on the technique to be used aremade by manufacturers and users.The responsibility for the development of an in-

terface standard suitable for direct implementationtherefore, rests exclusively on the users’ shoulders.Associations which are perhaps concerned as wellŽe.g., control associations or governmental institu-

.tions like PTB and small-sized to medium-sizedmanufacturing firms which depend on the users arepotential partners.

2.2. Line of action to be followed when drawing up astandard

The following approaches to the definition of thetechnical characteristics are conceivable.

Ž .1 Redefinition of the technique, tailored to thedefined field of application.

This is the most difficult way. It presupposes thatall those involved in drawing up the standard musthave great know-how. It usually requires parallelimplementation and testing; as a result, the processtakes a very long time and involves great expense.

Ž .2 Taking standards as a basis, which have provedtheir practical worth; if necessary, modifications mustbe made to adapt the new standard to the respectivefield of use.

This is the simplest and most promising way. Onecan take the experience gained by others as a basisand eliminate weak points which have meantimebecome apparent. It is, in fact, an essential character-istic of standardization that new standards are notdefined when standards already existing for the re-spective field can be used.

Ž .3 Taking a firm’s standard as a basis, which hasproved its practical worth; if necessary, modifica-tions must be made to adapt the new standard to the

Ž .latest trend updating .This way, too, is very simple and promising.

However, it contradicts the principle of equal treat-ment in standardization. Nobody may derive eco-nomic advantage from standardization. The use of afirm’s standard favours the manufacturer concerned.

The description of the technical characteristicsultimately is the standard. After publication of thedraft standard, implementations are carried out. Priorto final adoption and publication, a time limit forobjections is fixed which may lead to corrections.


2.3. Application of the standard

When the standard’s quality is confirmed duringimplementation, everybody is free to apply it. This isthe moment at which it also makes sense to design achip. Since many firms do not implement the stan-dard on account of the development costs or forshortage of staff, the chip manufacturer may make aprofit. The price of the chip is, of course, oriented oncompetition which for standardized systems is guar-anteed as there are other chip manufacturers orsoftware implementations.

3. Comparison with the manufacturer’s standard

From the purely technical point of view, thedefinition of a firm-specific interface is subject to thesame development as a standard, the initial situationbeing, however, far more favourable and not im-paired by opposed interests. However, the costs in-volved in the design of the interface must be borneby the manufacturer alone. He must market theinterface in order to recover the money spent on itsdevelopment. When there are no competitors, suit-able marketing activities may lead to a wide dissemi-

Ž .nation of the product e.g., a chip . It can be illus-trated by the example of the IBM-PC that firm-specific standards become actual standards only if1. a renowned manufacturer stands for the product

quality, and2. easy imitation by low-price offerers is possible.

The latter is the case when the product is notpatented and thus, not subject to licence fees. Inde-pendence from the original manufacturer, character-

ized by easy accessibility of the technique used, is ofparticular importance for successful standardization.

4. Present state of EPSI standardization

EPSI is a standard which has been defined in verygreat detail and which covers the complete networkin the forecourts of petrol stations. The Germanstandards DIN 66348 part 2 and DIN 66348 part 3are at the basis of EPSI, and these, in turn, are based

Žon international standards ISO 8482, ISO 1745, ISO.2111, ISO 9506 and are characterized by a specific

design of layers 1, 2 and 7 of the internationalreference model for open communication systemsaccording to ISO 7498. The other layers, too, areimplicit as can be gathered from the survey below.

4.1. The reference model according to ISO 7498

In this reference model, the communication pro-cess is represented in several layers, the aim being tomake it possible for the individual layers to bedesigned according to different standards, allowingopen, i.e., transparent, networks of different specificdesign to be defined, which can be used by every-body. The advantage of this layer representationbecomes obvious when one looks at Ethernet-basedPC networks which allow even different protocolsŽ .Apple and Microsoft, for example to be used simul-taneously. However, quite a number of transmission

Žprotocols do not allow all transmission media physi-.cal layers to be used as they are, for example,

sensitive to the execution time. In this referencemodel, a distinction is made between a total of sevenlayers:

Layer 1, physical layer EPSI definitions

The unit of data in this layer is the single bit For EPSI, the widely usedRS-485 interfaceŽ . Žin serial transmission systems . The electric with a full duplex bus system four-wire

.properties and special physical access technique acc. to ISO 8482 is defined in thismechanisms are defined in this layer. The layer. Physical access is centrally controlled byspecific design of the bus line and mechanical a control station. This wayof access is by no

Ž .locations plugs, etc. also belong to this layer. means sensitive to the execution time and canŽbe used for any physical interface even

.infrared, radio and optical fibres .


Layer 2, data link layer EPSI definitions

This layer contains the transmission protocol, In the data link layer, EPSI works with aincluding the definition of limitations, fault simple but highly efficient character protocol.security and fault correction. This layer also An efficiency of more than 50% is achievedmakes so-called ‘splitting’ possible, by which when transporting the data of a message ofdata from a link address can be transmitted to medium length from the layers above, theseveral physical addresses. The link is maximum efficiency being 91% for a blockestablished dynamically, according to the length of 128 characters. The block length istransport request. Accordingly, the link is basically variable so that layer 2 can becleared after transport has been completed. optimized as regards efficiency and latency.

Several devices can be addressedsimultaneously by a broadcast. Normal datatransfer takes place with directacknowledgement and includes faultcorrection by repetition.

Layer 3, network layer EPSI definitions

This layer manages network links In EPSI, every message contains a clearcharacterized by logical point-to-point links. identification for the assignment of twoThis layer also allows so-called multiplexing, application processes. This link number serveswhere several network addresses are linked to for routing and thus, has the same function as aone link address. network address. In EPSI, the assignment of

several link numbers to a link address isrealized by the link design in layer 7, with theapplications involved and their physicalposition in the network being stated.

Layer 4, transport layer EPSI definitionsŽ .This is the topmost last layer involved in the In EPSI, every service of the application

direct control of data transport. For example, protocol is identified by a special character forŽ .segmentation blocking of long message the beginning and end of a message. This

sections is made here. The flow check is also allows a clear segmentation to be made. Themade in this layer, which serves to protect the individual segments are identified by differentrecipient of the message from overloading by characters indicating the block end. The flow

Žthe sender when the recipient is not fast control is closely linked up with the link.enough . control of layer 2. The communicationpartner

Ž .does not initiate a link master or refuses aŽ .link slave when its input buffer is full.

Layer 5, session layer EPSI definitions

This layer comprises the management proper In EPSI, link management is connected withof the effective link. That is to say, the links the services establishment of a link, link

Ž .between the presentation layers layer 6 of clearance and discontinuation of link, whichthe various applications are established and also carry out initialization and de-initialization

Ž .concluded or discontinued here. When a link is of layer 7 MMS-initiate and MMS-conclude .established, this layer makes available for it an Other networks distinguish here between, foridentification for layer 6. Likewise, several example, connect and initiate, since many

Ž .messages can be retained in this layer before different applications not only MMS are


Žthey are transferred together to layer 6 so- linked via layer 5. Only the application of.called quarantine . MMS is provided in EPSI; no ‘quarantine’

operation is planned.

Layer 6, presentation layer EPSI definitionThe syntax is dealt with in layer 6. It is either In EPSI, the syntax used in the applicationpossible to select a specific syntax for data layer is also used for transport, the code is nottransport andror to change the syntax code. It changed. The presentation layer is, therefore,is basically possible to use three different completely empty.protocols for the link between twoapplications, i.e., the protocol of application 1,the transport protocol and the protocol ofapplication 2.

Layer 7, application layer EPSI definitionsVia layer 7, the user is given access to the Layer 7 of EPSI closely follows thenetwork. This layer must, therefore, offer all international standard ISO 9506

Žservices which are to be used by the user Manufacturing Message Specification,. Žprogram. Among these are, for example: MMS . In addition, special processes VMDs,

Ž . .1 identification of the desired communication Virtual Manufacturing Devices have been setpartners; up through which special network tasksŽ . Ž2 finding out whether communication partners synchronization of processes, change of

.are available; physical addresses, etc. can be carried out.Ž .3 agreements on protection mechanisms; Here, the link number is not used exclusivelyŽ .4 authentication of users of the communication; for the identification of a logic point-to-pointŽ . Ž5 specification of the quality of service link but also for special splitting relations oneŽ . . Žresponse times, tolerable error rate, etc. ; to all, one to many cf. Above, splitting in theŽ . .6 synchronization of co-functioning application data link layer .processes;Ž . Ž .7 identification evaluation of given data The other features of EPSI’s layer 7 arestructures designed above all with regard to an automatic

start of the network, even during the firstSyntax and semantics of the messages have start-up. Services have been defined for thisbeen specified for layer 7. purpose, which allow the user to have access

to the session layer, thus making the linkŽmanagement part of the user program cf. also

.session layer . The ways used to describe theŽ .data structures taken from MMS allow a

maximum degree of flexibility which is not yet,however, made use of in today’s petrolstations.

As can be gathered from the above survey, withŽ .the exception of layer 6 presentation layer , EPSI

allows for all layers of the reference model. DespiteŽ .this, one speaks in this case as with all fieldbuses

of a so-called three-layer model, with layers 1, 2,and 7 specifically designed. With this, one does not,

however, rise to the level of network functionalitiesbut to the actual message structure and the way inwhich messages are produced and evaluated.

In a network protocol in which all layers arespecifically designed, the messages are received byone adjacent layer, processed, and transferred to the


other adjacent layer. One can think of each layer asan independent process which adds something toeach message or takes something away from it. Thisprocess determines the period of time required forprocessing a message. This approach enables onelayer to transfer certain information for the samelayer in another device and to wait for appropriatereactions. It is also possible to transfer specific mes-sages which exchange layer-specific information. Thehigher levels in each of the communication systemsconcerned must not become aware of this.

The limitation to three layers only means thatonly three processes are effective for message pro-

Žduction and transmission the time structure in thephysical layer can usually be neglected compared

.with the other layers . The three-layer architecture is,therefore, basically faster. Nevertheless, all functionsof the layers omitted may have been allowed for.

4.2. Other technical characteristics

Even if seven communication layers are available,it is not yet guaranteed that the devices are com-puter-controllable. Applied to communication amongpeople, availability of seven layers means that thesame language is used during a work meeting, theparticipants’ technical qualification has been definedand the rules for the course of the meeting have beenestablished. It has not yet been said which topic is tobe dealt with and which aim is to be reached. WithEPSI, the latter is included in the communication

Ždescriptions for the individual devices DGMK re-.search reports 463-x . These definitions are basically

independent of the communication system, althoughthe rough structure is determined by the communica-tion system. The DGMK research reports are appli-cable to all communication systems

-which have a so-called clientrserver structure,-layer 7 of which is based on MMS, and-whose device implementation allows access from

Žapplication to certain communication layers 2, 3.and 5 in particular .

4.3. Current standardization actiÕities

The definition of the technical characteristics isone fundamental prerequisite for standardization. EP-

Ž .SIs communication system layers 1 to 7 is alreadystandardized in DIN 66348 parts 2 and 3. If EPSI is

Žto be extended to include other physical media e.g.,

.radio, infrared, power network, optical fibres , onlylayer 1 must be defined accordingly. In this case, one

Ž .can also switch to other standards e.g., IEC 1158-2 .Ž .No standards neither national nor international

are so far available for the definitions based oncommunication proper and contained in the DGMK

w xresearch report 463-3 1 . In fact, bodies are respon-sible for this which are not concerned with commu-nication itself. However, as communication is, in away, the corset for suitable definitions, the bodiesresponsible for application must either gain theknow-how in the communication field or cooperateclosely with the bodies exclusively concerned withcommunication.

As to EPSI, close cooperation between the stan-Ž .dards committee for tank plants NA-Tank and the

standards committee for length and form, sub-com-mittee ‘interfaces’ is at present under discussion. Asthe definitions in the DGMK research reports werealready made in close cooperation among communi-cation and petrol station specialists, the papers drawnup can be regarded as a basis for standardizationwork. There may be errors as regards the formalstructure of the papers, as the research reports weredrawn up with a view to using them within theframework of the research project. There are mean-while fixed rules for the drawing-up of standards,which have been harmonized on the European level.The work of the joint standards committee might befocused on bringing the research reports into a suit-able form.

References

w x1 N. Zisky, K. Jordan, B. Junge, V. Moravec, R. Patzke, H.Schumny, Standard interface in site electronics, Part III:Final report and communication descriptions. DGMK Re-search Report 463-3, Hamburg, November 1995.

Dr. Robert Patzke received his doctor-ate in electronic engineering in 1987from the University of Hannover, Ger-many. He is heavily involved in fieldbustechnology since 1986 and a member ofvarious committees concerned withfieldbus standardization. He takes care

Ž .for the Measurement Bus DIN 66348in CENELEC TC65CX and in diverseGerman committees. Since 1988, he is asenior manager of a small firm produc-ing measurement and fieldbus equip-ment, first and foremost for Measure-

ment Bus, Interbus S and Profibus. The present paper is the resultof his experiences in fieldbus technology.


Dr. Harald Schumny graduated earlyŽ1970, end 1972 Dr.-Ing. doctor engi-

.neer promotion at TU Braunschweig.Hereafter, scientist at Physikalisch-

ŽTechnische Bundesanstalt PTB, the.German national metrology institute in

Braunschweig for development of mea-surement technology basics for data ex-change by use of magnetic data storage

Žmedia 12 publications between 1973.and 1978 . Till 1977, additional teach-

ing at High School for Technology ofŽthe city of Braunschweig digital data

.processing and signal transmission . Since 1979, head of the PTBlaboratory ‘Measurement techniques and data acquisition’, from

Ž1981 German director of EUROMICRO European Association.for Microprocessing and Microprogramming . From 1984, leading

of courses and seminars in the field of data acquisition andprocessing by use of PCs and digital interfacing. More than 50publications and course books result from this period. Since 1985,

Ž .Editor-in-chief one of two of the international journal ComputerStandards and Interfaces, from 1988, editor of the book ‘Personalcomputer in laboratory, experiment and test field’, Springer pub-lisher Berlin, Heidelberg, New York. Since 1992, director andprofessor at PTB for ‘Metrological Information Technology’.Main fields of interest are data acquisition, electrical measure-ments, analog-to-digital conversion, interfacing, computer-in-tegrated measuring systems.

Dr. Norbert Zisky studied physics atHumboldt University in Berlin. From1975 to 1981, studied information tech-niques and electronics at TU Chemnitzresulting in an engineering degreeŽ .Dipl.-Ing. . Until 1990, scientist withcenter points of the design, constructionand scientific research of computer-con-trolled instruments for optical measure-ments. Since 1991, scientist atPhysikalisch-Technische Bundesanstaltin Berlin, and now head of the labora-tory for ‘Measurement Data Acquisition

and Data Transfer Technology’, the research field of which in-cludes interfacing, buses and networks. Chief topics are field andsystem buses, development of automated interface test instru-ments, and development of communication interfaces. In 1996

Ž .doctorats promotion Dr.-Ing. at TU Braunschweig.

standardization aspects

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