1、ITU-T RECIN*F-SBL 93 W 4862571 0582204 T85 INTERNAT ONAL TELECOMMI ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU NICAT ON UNION F.581 (03/93) OPERATIONS AND QUALITY OF SERVICE DIRECTORY SERVICES GUIDELINES FOR PROGRAMMING COMMUNICATION INTERFACES (PCls) DEFINITION: SERVICE RECOMMENDATION ITU
2、-T Recommendation F.581 (Previously “CCITT Recommendation”) ITU-T RECMN*F.583 93 II 4862593 0582205 931 O FOREWORD The IT Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The IT-T is responsible for studying technical, operating an
3、d tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, p
4、roduce Recommendations on these topics. I3V-T Recommendation F.581 was prepared by the ITU-T Study Group I(l988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). NOTES 1 As a consequence of a reform process within the International Telecommunication Union (IT), the CC1-I ceased to exi
5、st as of 28 February 1993. In its place, the iT Telecommunication Standardization Sector (IT-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no c
6、hange has been made in the text to references containing the acronyms “CCITT, CCIR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. 2 telecommunication admini
7、stration and a recognized operating agency. In this Recommendation, the expression Administration” is used for conciseness to indicate both a O IT 1993 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including phot
8、ocopying and microfilm, without permission in writing from the IT. - ITU-T RECMN*F.581 93 m Y862591 058220b 858 m CONTENTS Introduction 2.1 General 2.2 Applicability . Possible benefits of the PCIs 3.1 For implementors 3.2 For users . 3.3 For carriers EIS requirements 4.2 Dependency 4.3 Flexibility
9、4.4 Extensibility 4.5 Multiple applications 4.6 Easy implementation and testing 5.1 Location of the interface . ! . 5.2 Functional description 5.3 Formal description 5.4 Presentation of the information . General functional model . Application related interfaces . 7.1 Defuiitions 7.2 General features
10、 NetworWProtocol related interfaces . 8.1 Definition 8.2 General features scope 4.1 Independence General guidelines for defining PCIs . Annex A . Definitions Appendix I . Examples . Telefax 3 on PSTN . ISDN Lower Layer Module 1.1 1.2 Page 1 2 2 2 2 2 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 5 5 5 ITU-T RECMN*F
11、m58L 93 = 48b2591i 0582207 794 Recommendation F.581 GUIDELINES FOR PROGRAMMING COMMUNICATION INTERFACES (PCIs) DEFINITION: SERVICE RECOMMENDATION (Helsinki, 1993) 1 Introduction 1.1 Today, telecommunication needs in the microcomputer world are quickly increasing. -T senices are defined to meet these
12、 needs, but due to the technical and commercial context of the microcomputer world some concrete problems may arise. a) Techicd uspects In some implementations communication equipment may be composed of hardware and software modules which come from various manufacturers. These modules must exchange
13、information to provide the user with access to ITU-T services, but manufacturers may use different working methods and vcicahularies. Therefore, adding new software and hardware to existing configurations involves very detailed knowledge of different areas: telecommunication aspects, computer aspect
14、s, hardware and software aspects. Setting up such equipment requires the help of experts, whereas using ITU-T services only requires a very basic knowledge of the technical aspects. The consequence of such a situation is often a lack of integration of the communication dialogue with the local softwa
15、re dialogue. b) Commercial uspects Using hardware and software modules without standardized interfaces may mean buying software and hardware pieces designed to fit together well. The definition of a public universal interface for a specific communication application (such as facsimiile, Teletex, tel
16、ex, etc.) gives to the user more freedom in the choice of the products. Most of these difficulties regarding Softwares may be solved by the standardization of public inter- application interfaces. 1.2 “Programming Communication Interfaces*”. Interfaces allowing access to software providing a 1T-T co
17、mmunication service are called PCIs for Two levels of PCIs are defined: a) Application related interfaces which allow any local Application* (LA) to access any Communication Application* (CA). One example of an application related interface is the APPLUCOM, which is described in Recommendation T.611
18、. NetworkProtocol related interfaces, which allow any LA or Communication Management Entity* (CME) to access any Lower Layer Module* (LLM). Nehvork/protocol related interfaces are under study. b) NOTE -The definition of new terms indicated with (*) may be found in Annex A. Examples are shhown in App
19、endix I. 1.3 technical Recommendations. The information to be exchanged through the interfaces and the way to exchange them is subject to the PCIs ?he exchange method describes the procedures that are performed to convey the information between SOfhVaE modules on each side of the interfaces. Recomme
20、ndation F.581 (03/93) 1 ITU-T RECMN*F.SBL 93 W 48b259l1 0582208 b20 2 Scope 2.1 General 2.1.1 The applicability of PCIs requires the definition of: This Recommendation gives guidelines from a service point of view for the definition of PCIs. a) the information to be exchanged through the interface.
21、These messages are defined Operating System and programming language independent, but ITU-T service definition dependent. Therefore, they are defined in technical ITU-T Recommendations; the way to convey (Exchange method) this information through the interface. b) 2.1.2 The main objective of this Re
22、commendation is to define: - - - - the possible benefits of these PCIs; a common vocabulary for all PCIs definitions; a general functional model allowing all PCIs to work together if required; general rules to be taken into account in the definition of PCIs. 2.1.3 Technical definitions of PCIs are d
23、efined in related Recommendation(s): T.611: Programming Communication Interface (PCI) APPLICOM for Facsimile Group 3, Facsimile Group 4, Teletex and telex services. NOTE - Other Recommendations are under study. 2.2 Applicability The provision of Programming Communication Interfaces is not mandatory
24、for participating in a IT-T service. The intention is to help developers by giving them general guidelines for the integmtion of -T services in their products. It must be kept in mind that PCIs leave a certain freedom to manufacturers, who may implement one or more of the possible PCIs and may exten
25、d them for private needs. 3 Possible benefits of the PCIs Possible benefits which could be expected from the definition of the PCIs concern implementors, users and carriers. They are: 3.1 For implementors a) PCIs help developers by providing them with common standardized interfaces. Implementors of
26、Communication Applications* (CA) will find in PCIs Recommendations practical details concerning the implementation of standardized IT-T services. On the other hand, implementors of Local Applications (LA) will no longer need to become experts of telecommunication protocols. For both categories, time
27、 taken to develop the implementation may be shortened and developments may become cheaper because developers will no longer need to adapt their products to many other products, whose features change frequently. As another expected result, the PCIs might shorten the development of new applications as
28、 these applications could benefit from existing communication applications that comply with ITU-T service rules (provided these existing applications also conform to PCI). NOTE -The definition of new terms indicated with (*) may be found in Annex A. b) c) d) 2 Recommendation F.581 (03/93) 3.2 For us
29、ers a) The main expected result of using the PCIs is gaining uniformity in the use of IT-T services. Thanks to the Prcigramniing Comtnunicatioii Interfaces, users will be able, for insmce, to send a document using the facsimile service, telex service or the Teletex service without noticeable differe
30、nces. However, service constraints described in related Recommendations are still applying. PCIs are designed to provide the end user with the ability to set up, extend and use any type of machine configuration (i.e. stand-alone machines, LANs, etc.) in order to send d receive files using various IT
31、U-T services in a very simple and uniform way. b) K( )TE - PCIs art: not in competition with LANs standards. PCIs provide the ineatis to hide system, software and hardware vririatioiis from end-users, thus facilitating the use of ITU-T services. 3.3 For carriers Traffic should increase as more equip
32、ment would offer communication features resulting from the universal interfaces, and users should he encouraged to communicate due to better dialogue ergonomics. 4 PCIs requirements 4.1 Independence The functional definition of a PCI is independent of: - - the computer type, the operating systems an
33、d progr,amming languages: the system configuration. It may be implemented in every case of machine configuration, e.g. stand-alone machines, LAN, etc. Furthermore, the choice of a presentation of information, independent of operating systems and programming languages should allow PCIs to be easily p
34、ortable from one operating system to another. The possible choices of programming languases are defiried in the technical Recommendations. 4.2 Dependency The furictional definition of a PCI depends on the ITU-T services provided by the cornmunication module to be iUWXd. 4.3 Flexibility KI3 aiiow iex
35、ibility iti itnpleinetitaticitis, for the sake of product differentiation. PCIs definition may include a mhinisioii mechanisin which allows iui application to request another for processing a specific function. In this case, PCIK technical Recommend;itions define the functions which should nonnally
36、be performed by each application. 4.4 Extensibility Private extensions arc passible without jeopmiking the overall performance of the PCIs. Implenientation docuinentation will specify how these extensions may be riscd by otlier application softwares. Technicd Recantiiaidatioiis should provide for di
37、 extensions. 4.5 Multiple applications Multiple software modules Iocated above ai interface may access one or multiple software modules located below the same interface. Since this requirement is operating systems dependant, it is completely maiaged by the PCI exchange method. Recommendation F.581 (
38、03/93) 3 ITU-T REClN*F.581 93 W 48b2591 0582230 289 I Procedures allowing a correct transfer of requests and responses between two applications should be independent of the physical location of these applications. Multiple local applications may be interfaced to one or several communication applicat
39、ions. 4.6 Easy implementation and testing The implementation of a PCI should be easy in order to gain a widespread acceptance. It should give additional information for a better implementation of the concerned applications, in order to avoid errors. The testing of a PCI should be simple. NOTE - Tech
40、nical Recommendations should point out how a “real” implementation has to behave, and should give guidelines for implementors (in Appendix I). 5 General guidelines for defining PCIs 5.1 Location of the interface As already stated in the introduction two general scopes of PCIs are defined, the Applic
41、ation related interfaces (located at the higher layers of the OS1 model) and the Network/Protocol related interfaces (located at the network and protocol dependent layers). Non-OS1 applications should be incorporated depending on the individual PCIs. In order to avoid any misunderstanding, the ITU-T
42、 services, protocols, networks which are covered by the PCI must be clearly identified. 5.2 Functional description The functions which can fulfill the interface should be described. The description of functionality sha be completely independent of the equipment. 5.3 Formal description Messages inter
43、changed through the interface should be described. At this step, the interface definition is required to be equipment independent. 5.4 Presentation of the information For application related interfaces the presentation of information (coding scheme) independent of operating systems and languages sho
44、uld be chosen. The description of this may form a part of technical Recommendations. The description of the presentation of the information concerning networkprotocol related interfaces is not necessarily independent of operating systems and languages. The description may be a part of the technical
45、Recommendation, if it is operating and languages systems dependent. Otherwise, it may form an appendix. Technical Recommendations give more details on this aspect. 6 General functional model The concept of Programming Communication interfaces covers two different levels of interfaces: - - applicatio
46、n related interfaces, one example is the APPLI/COM interface T.611; networkprotocol related interfaces, which are under study for the time being. The interfaces are independent of each other and one may be specifiedimplemented on its own. Furthermore, one level may contain more than one interface, w
47、hich may coexist independently of each other. The location of each interface level relative to the other is given in Figure 1 “PCIs general model”. 4 Recommendation F.581 (03/93) Local appim I Applicaticn related interfacec l NetworWProbcd related interfaces FIGURE 1R.581 PCIs general model Communic
48、ation application (CA) 7 Application related interfaces 7.1 Definitions application related PCIs: Frovide interfaces to access one or more ITU-T services. The interfaces are provided by the Communication Management Entity“ (CME). The CME may use NetworWProtocol related XIS for ITU-T network and prot
49、ocol access. The functionality and behaviour of the interface shall effectively uncouple an application from ITU-T service properties. NOTE -The definition of new terms indicated with (*) may be found in Annex A. 7.2 General features Functionality und presentation of messases and the exchcange method shall be designed independent of hardware and systems softwxc whenever possible. Application related interfaces may provide error handling capbilities and shall be able to be tested. The functionality of application related XIS may be task submission oriented. Reco
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