Mạng và viễn thông P40

Chia sẻ: Hug Go Go | Ngày: | Loại File: PDF | Số trang:18

Thêm vào BST

Báo xấu

65
lượt xem 4
download

Mạng và viễn thông P40

Mô tả tài liệu

Download Vui lòng tải xuống để xem tài liệu đầy đủ

Technical Standards for Networks In the past, telecommunications networks have been evolved in the minds of their designers to meet well defined but changing user demands. These broadly innovative influences are bound to persist and users can look forward toever more sophisticated telecommunications services in the future. Itwas onlyin themid-1960s that customer-dialled international telephone callsfirst became possible, and in those days such calls were for therich alone.

Chủ đề:

Bình luận(0) Đăng nhập để gửi bình luận!

Lưu

Nội dung Text: Mạng và viễn thông P40

Networks and Telecommunications: Design and Operation, Second Edition. Martin P. Clark Copyright © 1991, 1997 John Wiley & Sons Ltd ISBNs: 0-471-97346-7 (Hardback); 0-470-84158-3 (Electronic) 40 Technical Standards for Networks In the past, telecommunications networks have been evolved in the minds of their designers to meet well defined but changing user demands. These broadly innovative influences are bound to persist and users can look forward toever more sophisticated telecommunications services in the future. Itwas onlyin themid-1960s that customer-dialled international telephone callsfirst became possible, and in those days such calls were for therich alone. Nowadays the advance of technology has made themso much cheaper thateveryone takes them for granted. In late 1960s everyone the marvelled at thefirst live satellite broadcasts; now there areso many satellites in space that many of them no longerhavenames,only longitudinal geographic location references. Every day the world’s communicators move larger and largervolumes of video, text, speech, and data informa- tion around theglobe, and all without a second thought. The revolution in communications that we haveseen, and theever-wideningscope forinformationtransfer, have only come about through an almost fanatical emphasis on the internationalcompatibility of telecommunications networksandequipment,underpinned by worldwideagreement onthe technical standards without which interconnection between networks in different countries and the interworking of different network types would be impossible. This chapterdiscusses the variousbodies involved in setting these standards. It outlines inparticulartherecommendations of ITU (International Telecommunications Union), the world’s most authoritative body on telecommunications technical standards. 40.1 THE NEED FOR STANDARDS Whenevertwo or more pieces of equipment,built by different people or different manufacturing companies, arecalled on towork harmoniously together within the same network, there is a need for technical standards. The standard defines comprehensively the interface, or set of interfaces to be used between various equipments. It describes the functions that each of the equipments are required to perform, and it ensures that the signals passed between the equipments are fit for their purpose, and unambiguous. Only a network designed and built in isolation could exist without carefully defined and documented technical standards for the interfaces. Such networks are extremely 723
724 STANDARDS TECHNICAL FOR NETWORKS rare,for even whenmanufacturersdeveloptheirownspecialinterfacesforinter- connecting two pieces of their own equipment, these interfaces usually conform to their own documented proprietary standards. An example of a proprietary standard is the systems network architecture ( S N A ) (described in Chapter 18) which can be used as the basis for network design(called an architecture) interconnecting computer systems. SNA is similar to ITU’s (or ISO’s) OS1 model, but was developed by the IBM cor- poration and was in use by their customers before the ITU standards had been agreed. Most networks are from equipment supplied by many different manufacturers, who usually cooperate with the network operators and other interested parties to define the standards necessary to ensure correct interworking of equipment. The application or potential of any particular standard is usually the determining factor in how many partiesneed to beinvolvedindeveloping and documenting it. Consequentlymany slightly different groupings of manufacturers, network operators, users, and regulatory bodies, both national and international, have sprung up over the years to address the developmentofvariousdifferentsets of standards.Eachgrouping(often calleda standards body) tends to specialize in the interfaces required between particular types of equipment(saycomputers,orfacsimilemachines, or customerpremisesequipment ( C P E ) or safety). The remainder of the chapter describes a number of the most prom- inent ones. 40.2 WORLDWIDE INTERNATIONAL STANDARDS ORGANIZATIONS International network interconnectionshave always presented somethingof a challenge forthe engineers developingthem.Historically, international telecommunications between different countries have been provided by means of gateway switches, which have provided a means for interfacing and interworking a common international stand- ard with the plethora of slightly differing national networks. International standards have thus provided the foundationof the recent boom in international communication. The boom is likely to continue so long as each national network evolves slowly towards the international standard, leading ultimately to a homogeneous worldwide network. However, this is only one of the benefits to be derived from international standards; no less important, withusers of even thesmallestnetworksinsisting on conformance, terminal equipment manufacturers will beobliged to produce devices of worldwide compatibility. The amount and quality of international standardization has improved rapidly in recent years. One of the practices which has improved standards is the definition not only of interfaces andprotocols,butalso of theproceduresfor conformance and compatibility testing. Such procedures are defined in standards called PICS (protocol implementation conformance statements) and PIXITs (protocol informationextra information f o r testing). The most important worldwide standards organizations in telecommunications are the International Organization for Standardization ( I S O ) (colloquially the International Standards Organization)and theInternational Telecommunications Union (ZTU).A third body, but only important in the agreement of standards for satellite working, is the International Telecommunications Satellite Organization, called I N T E L S A T .
INTERNATIONAL WORLDWIDE STANDARDS ORGANIZATIONS 725 International Organization for Standardization (ISO) The I S 0 is a ‘voluntary’ organization, composed of and financed the national stand- by ards organizations (e.g. British Standards Institute ( B S I ) , American National Standards Institute ( A N S I ) , etc.) of each of the member countries. Like each of its component national organizations, the I S 0 lays down standards for practically every conceivable item, not only telecommunications, but also colour scheme for electrical wiring, and the even the standard sizes for paper (e.g. A3, A4, etc.). The organization has a number of sub-committees, but in the main it does not produce standards from scratch. It tends merely to ‘brush-up’ standards submitted by its member organizations. In this way the local area network ( L A N ) standard I S 0 8802 started life as IEEE802, generated initially by the American Institution o Electrical and Electronic Engineers ( I E E E ) . f Address International Organization for Standardization Rue de Varembe, 1 Case Postale 56 CH-l21 1 Geneve 20 Switzerland Tel: (41) 22 749 0111 International Telecommunications Union ( I T U ) The ITU is an agency of the United Nations, responsible for overseeing all aspects of telecommunications. Organizationally, theITU is split into four permanent parts, all of which are headquartered in Geneva.Theseareshown in Figure 40.1. TheGeneral Secretariat is responsible for overall administration, finance, and publication of regula- tions, journals and technical recommendations (their name for standards). The Radio- communication Bureau ( B R or I T U - R ) serves in two functions, first as a ‘custodian of international public trust’, regulating the assignment of radio frequencies throughout the world, and so preventing interference between radio stations (this responsibility used to be carried out by the ITU under the organization called IFRB (International (radio) Frequency Registration Board). Second, the ITU-R acts as a consultative com- mittee which generates technical standards and reports regarding radiocommunication (thisfunctionwasformerlycarriedout by thepredecessorbodyknown as CCIR The (Consultative Committee for Radiocommunication)). Telecommunications Standardi- zationBureau ( T S B or I T U - T ) is themain consultative committee whichgenerates INTERNATIONAL TELECOMMUNICATIONS UNION (ITU) Standardization (BR or ITU-R) (TSB or ITU-T) Figure 40.1 Organization of the ITU
726 STANDARDS TECHNICAL FOR NETWORKS technical standards for telephone/telegraph networks (including data networks). The I T U - T ( I T U standardization sector) replaces the former body, known as the C C I T T (International Telegraph and Telephone Consultative Committee). The fourth partof the ITU, set up by the plenipotentiary meeting in June 1989 is the BDT (Bureau for the Development of Telecommunications). The BDT has the same status as the ITU-R and ITU-T in its aimis to secure ‘technical cooperation’ but in addition it has a prime role in raisinghelp and finance to helpthe less-industrialized countriesdeveloptheir tele- communicationsnetworks.Morethan 150 countriesaremembers of the ITU and participate in the workof the consultative committees. Delegatesto the individual study group meetings comprise not only the main public network operators, but alsoscientific and industrial organizations, private companies and equipment manufacturers. In the main, the study groups generate recommendations from scratch, based on the contribu- tions of delegates. ITU-Tapproves new recommendations at the WTSC (World Telecommunications Standardization Conference) which has replaced the four yearly C C I T T plenipotentiary meeting which formally approved the coloured ‘books’ of technical standards. Address International Telecommunications Union Place de Nations CH-1211 Geneve 20 Switzerland (Same address for ITU-R, ITU-T and BDT) Tel: (41) 22 730 5111 (Sales and Marketing Service) Tel: (English): (41) 22 730 6141 Tel: (French): (41) 22 730 6142 Tel: (Spanish): (41) 22 730 6143 International Electrotechnical Commission ( I E C ) Also known as the Commission Electrotechnique Internationale ( C E I ) , the IEC exists to promote international cooperation on electrical and electronic standards. It works in a similar manner to the ISO, gaining an international consensus of opinion and issuing standards in main nine fields, the important most to us being those affecting Telecommunicationsand Electroniccomponents andthoseon Telecommunications equipment and information technology. The IEC has equal status and works in close cooperation with the ISO, whose prime interest is in the non-electrical fields. Address International Electrotechnical Commission Rue de Varembe, 3 CH- 1202 Geneve 20 Switzerland Tel: (41) 22 919 02 11
REGIONAL AND NATIONAL STANDARDS ORGANIZATIONS 727 INTELSAT The International Telecommunications Satellite organization is run by subscription between the world’s main international public network operators. Its prime purpose is to develop, procure, and operatesatellite services between countries. In support of these aims it develops its ownstandards specifically for the satellite service (e.g. from satellite earth station to satellite in space, or for multiple access operation (see Chapter 33)). Address INTELSAT 3400 International Drive NW Washington D C 20008 United States of America Tel: (1)-202-944-6800 40.3 REGIONAL AND NATIONAL STANDARDS ORGANIZATIONS A number of regional and national standards organizations are also in existence. In some cases these duplicate the international standards, and may even be at variance with them, a situationwhich is bound to persist, because it takes a long time to agree on an international standard. However, some users cannot wait but feel obliged to develop their own ‘interim’ standards, and these too tend to persist even after the emergence of the world standard, because of the investment tied up in them. Notable regional and national organizations involved in such standards are as follows. Comite‘ Europe‘en de Normalisation ( C E N ) The CEN is theEuropean equivalent of the ISO; constituted of membernational standards bodies, it generates European Norms (ENS), but unlike I S 0 standards ENS are mandatory standards in the signatory countries to the CEN. CENELEC, a related organization, is theEuropean equivalent of theIEC, generatingEuropeanelectro- technical standards. Addresses Comite Europeen de Normalisation Rue de Stassart 36 B- 1050 Brussels Belgium Tel: (32) 2 550 08 11 CENELEC Rue de Stassart 35 B- 1050 Brussels Belgium Tel: (32) 2 519 68 71
728 TECHNICAL STANDARDS FOR NETWORKS European Conference for Posts and Telecommunications ( C E P T ) The Telecommunications Commission (T Com) of the CEPT was until 1988 promi- nent, in muchthesame way asthe CCITT (the forerunner of theITU-T), in the developmentofEuropean telephone telegraph anddatanetworksstandards,and manyCEPTrecommendations haveformedthebasis of the CCITT (now ITU-T) recommendations. However, in 1988, prompted by the desires of the European Union ( E U , thencalledthe EuropeanEconomicCommunity, E E C ) to quicklydevelopthe network interfaces needed for establishment the of pan-European a network infrastructure,the CEPT elected tohand overallitstechnical standards develop- mentwork to a new permanentlystaffedorganizationcalledthe ETSI(European Telecommunications Standards Institute). Nevertheless, the CEPT lives on, an as organizationofEuropean public telecommunications operators discussingmutual strategy and planning, including management of the radio spectrum in the European region. Address CEPT Information Desk European Telecommunications Office (ETO) Holsteinsgade 63 DK-2100 Copenhagen Denmark Tel: (45) 35 43 25 52 European Telecommunications Standards Institute (ETSI) Funded in part by EuropeanUnion money, theETSI wasfoundednearNicein France in 1988 to develop network the interfaces andother technical standards necessary for a homogeneous, and pan-European telecommunications network. It has over 370 members from more than 30 countries in the CEPT and the European Free Trade Association (EFTA), as well as European Union states. The technical work is undertaken by full time staff, seconded from public network operators, manufacturers, trade associations, users, research bodies and national standards bodies. In addition, a number of special voluntary working parties have been established to deal with priority items. The ETSI is composed of a technical assembly and a permanent secretariat, but the standardsdevelopmentwork is carried out by workingpartiesand projectteams. Technical documents produced by ETSI may become one of three types of document, as listed below e E N or E N V (European Norm) Standards;to become ENSortemporaryENS (ENVs), the standard needs to be put up for formal adoption by CENjCENELEC e E T S (European Telecommunication Standards) ETSs are voluntarily accepted standards and guidelines e NETS (Normes EuropPenesde Tklkcommunications), these are the most important standards, because they are mandatory across Europe
REGIONAL AND NATIONAL STANDARDS ORGANIZATIONS 729 In addition, ETSI also issues ETRs (European Technical reports) which provide useful technical information for the design of equipment and telecommunications networks, but these do not have the status of standards. Address European Telecommunications Standards Institute 650 Route des Lucioles F-06921 Sophia Antipolis Cedex France Tel: (33) 4 92 94 42 00 secretariat@etsi.fr Tel: (Publications office): (33) 92 94 42 41 European Computer Manufacturers Association ( E C M A ) A consortium of European computer manufacturers, working on a voluntary basis to develop computer interconnection standards. The ECMA often debated standards have within Europe before contributingto the ITU.An example is the OS1 transport protocol, ECMA-72 and I S 0 8072. Address European Computer Manufacturers Association Rue du Rhone, 114 CH- 1204 Geneve Switzerland Tel: (41) 22 849 6000 American National Standards Institute ( A N S I ) ANSI is a voluntary national standards organization of the United States of America, and is a member the It of ISO. is theUnitedStates clearing house stand- for ards, generally adopting standards proposed by smaller companies and organizations withintheUnitedStates. Notable achievementsof ANSI have been the computer character code ASCII (American standard code f o r information interchange) and the computerprogramminglanguages, COBOL and F O R T R A N . ASCIIwasthefore- runnertoITU-T’sinternationalalphabetnumber 5 (IA5,ITU-Trecommendation T.50) which defines the alphabet in which computers ‘talk’ to one another. Address American National Standards Institute 11 West 42nd Street New York NY 10036 United States of America Tel: (1)-2 12-642-4900
730 TECHNICAL STANDARDS FOR NETWORKS Electronic Industries Association ( E I A ) The EIA is a national trade association, developing electrical standards primarily for North America. Notable achievements of the EIA havebeen the RS-232 (forerunner to ITU-T V.24) and RS-449 (forerunner to ITU-T V.36) interfaces used between computer equipment. Address Electronic Industries Association 2500 Wilson Boulevard Arlington Virginia VA2220 1 United States of America Tel: (1)-703-907-7500 Institute of Electrical and Electronics Engineers (IEEE) This is a professional institution based in the United States but for electrical engineers based anywhere in the world. It lays down professional and technical standards and codes of conduct. A notable achievement of IEEE was the IEEE local area network ( L A N ) standards inthe 802 series, first published in 1983. These are now used throughout the world as the standards for localarea networks (LANs). Theyhave subsequently been adopted by the International Organization for Standardization as I S 0 8802. Address Institution of Electrical and Electronic Engineers United Engineering Centre 345 East 47th Street New York NY 10016 United States of America Tel: (1)-212-705-7900 Publications from Customer Services Tel: (1)-908-981-0060 Exchange Carriers Standards Association (United States) Commonly calledtheT1-Committee,aleadingbodyinagreeingstandardsforthe deregulatednetworks of theUnitedStates.The TI-committee (formerlyExchange carriersstandardsassociation) is opentoanysubscribingmembers,buttheseare mainly United States exchange carriers.Standards under the auspice T1 include most of United States PTO (or exchange carrier) networking standards (e.g. T1-ISUP, the T1 version of the number integrated 7 services digital network user partsignalling described in Chapter 12. T1-ISUP is used mainly in the United States). Another T1 standard is the B-ICI (Broadband Inter-Carrier Interface) used to interconnect ATM networks of different carriers. The standards work itself is carried out by a number of sub-committees called variously T1-D1, Tl-XI, etc.
REGIONAL AND NATIONAL STANDARDS ORGANIZATIONS 731 Address Alliance for Telecommunications Industry Solutions (Standards Committee T1) 1200 G Street NW Suite 500 Washington DC 20005 United States of America Tel: (1)-202-434-8845 Society o Manufacturing Engineers ( S M E ) f This is an American society formed of subscribing manufacturing organizations. It is responsible for the early development work on the manufacturing automation protocol ( M A P ) and the technical and ofice protocol TOP). Address Society of Manufacturing Engineers PO Box 930 1 SME Drive Dearborn Michigan 48 12 1 United States of America Tel: (1)-313-271-1500 Telecommunication Technology Committee (TTC) (Japan) This body (set up in Japan at thetime of liberalization of telecommunications network services) is responsible for laying down network interface standards. It is composed primarily of leading Japanese scientists and engineers from network operators and equipment manufacturers. same way that T1 and ETSI the In the set pace for telecommunications standards in North America and Europe, respectively, so the TTC sets the de facto standards for the South East Asian region. Address The Telecommunication Technology Committee Hamamatsu-cho Binato-Ku 1-2-1 1Hamamatsu-cho Susuki Building Minato-Ku Tokyo 105 Tel: (81) 33 43 21551 British Standards Institution ( B S I ) As an example of the many other national standards organizations, the British Stand- ardsInstitution ( B S I ) producestelecommunications andotherstandardsand is a member of the ISO.
132 TECHNICAL STANDARDS FOR NETWORKS Address British Standards Institution Linford Wood Milton Keynes MK14 6LE United Kingdom Customer service and sales, Tel: (44) 181 996 7000 40.4 REGULATORY STANDARDS ORGANIZATIONS As many of the world’s governments have recently become keen to deregulate their telecommunicationsmarkets,allowingfreecompetitionparticularlybetweenmanu- facturers of customer premises equipment ( C P E ) as well as between network operators, there been has an increasing need forcertainnetworkinterfacestandards to be mandated by law, and ‘policed’ by a regulating body. (Customer premises equipment ( C P E ) is the general name applied to any type of equipment connected to the public network. Thus telephones, computer terminals and other similar devices are all CPE.) The use of a mandated standard for the interface between network and CPEensures the protection of the network operator’sstaff and equipment,meanwhile also assuringCPE manufacturersthat theirequipmentoperatessatisfactorilyoverthenetwork.The following organizations are active in laying down mandatory technical standards. European Telecommunications Standards Institute (ETSI) Already mentioned in this chapter, one of the first jobs of the ETSI was to lay out the CPE-to-network interfaces that become mandatory in each of the European Union member states and other signatories of the CEPT’s memorandum of understanding. Thestandardsareknown as NETs(Normes EuropPennes de Telecommunications, French for ‘Europeantelecommunications standards’). Once a NET has been adopted, both public network operators and CPE manufacturersneed to prove that their equip- ment conforms to the interface, before legal NET of approval is given either for the launch a new network service or for the saleof CPE. TheNET programme, however, is signifi- cant in that CPE approval and certification (the‘green dot’) will be valid Europe-wide (in any one of the signatory countries). Table 40.1 lists the original mandatory NETs. Federal Communications Commission (FCC) The FCC is the regulatory body in the United States, reporting directly to congress, which lays down the code practice to which network operators and equipment manu- of facturers must conform. Address Federal Communications Commission 1919 M Street NW Washington DC 20554 United States of America Tel: (1) 202-418-0260
DARDS REGULATORY 733 Table 40.1 MandatoryEuropeanTelecommunications Inter- face Standards ~~ ~ Normes Europeenes de Telecommunications (NETS) Access Group NET 1 X.21 (Chapter 9 ) NET 2 X.25 (Chapter 10) NET 3 ISDNbasic rate interface(Chapter 10) NET 4 PSTNnormaltelephoneaccess NET 5 ISDN primary interface rate (Chapter 10) NET 6 X.32 (Chapter 10) NET 7 ISDNterminaladaptor (Chapter 10) Mobile Group NET 10 Cellular network access NET 11 Telephonyterminal Modems Group NET 20 General modem NET 21 V.21 modem NET 22 V.22 modem NET 23 V.22 bis modem NET 24 V.23 modem NET 25 V.32 modem Terminals Group NET 30 Group 3 facsimile terminal NET 31 Group 4 facsimile terminal NET 32 Teletex terminal NET 33 Telephonyterminal Ofice of Telecommunications (Oftel) Oftel is theregulatorybodyfortelecommunicationswithintheUnitedKingdom, overseeing the activities of all public and private telecommunications operators and users. It is part of the UK government’s Department of Trade and Industry. Of late, Oftel has focussed its regulations on controlling the conduct of operators in the U K rather than on technical standardization. Standardization of technical interfaces for interconnection of networks has been delegated to the Network Interconnection Coordination Committee (NZCC) while questions of quality and network design have been left to individual user choice. Address The Office of Telecommunications 50 Ludgate Hill London EC4M 755 United Kingdom Tel: (44)-171-634 8700
734 NETWORKS FOR STANDARDS TECHNICAL British Approvals Board for Telecommunications ( B A B T ) BABT is the independent body in the United Kingdom which undertakes customer premises equipment (CPE) approvals, confirming that submitted equipment conforms to thenational network interface. BABT is the UK’s main registered bodyfor approvals which will apply throughout the European Union and other NET signatory countries. Address British Approvals Board for Telecommunications Claremont House 34 Molesey Road Hersham, Walton-on-Thames Surrey KT12 4RQ United Kingdom Tel: (44) 932 251200 Bundesamt fir Zulassung in der Telekommunikation ( B Z T ) BZT is the German equivalent of BAPT, being the responsible agency in Germany for testing and issuing of technical approvals certificates. Address Bundesamt fur Zulassung in der Telekommunikation TalstralJe 34-42 66 119 Saarbrucken Germany Tel: (49) 681 598-0 40.5 OTHER STANDARDS-PROMOTING ‘FORA’ Towards the end of the 1980s a number of organizations were becoming increasingly frustrated because of the bureaucratic manner in which the official standards organiza- tions operated, because of the constraining rules of procedure, and particularly by the long maturation time then required to develop and agree new technical standards. For equipment manufacturers this was resulting in lost sales, as potential purchasers held off until the standards were agreed. For network operators this meant a hold-up in the opening dates of new services. In a number of fields the frustration was so great that a number of like-minded organizations set about forming debating and lobbying fora to promote the quicker development of standards. Also typical is a permanent member- financed company to organize the work of the forum and promote its results. Typical also is a less formal procedure of meetings and contributions. Much of the work and communication within the working groupsis instead conducted via electronic mail, and members may be obliged to own an electronic mailbox as a condition of membership. The most well-known of such fora are the Frame Relay Forum, the Network Manage- ment Forum and the ATM Forum.
OTHER STANDARDS-PROMOTING ‘FORA’ 735 Frame Relay Forum TheFrame Relay Forum was establishedwiththeobjective to develop,agree and promote frame relay networks Address Frame Relay Forum 303 Vintage Park Drive Foster City California CA94404 United States of America Tel: (1) 415 578 6980 www.frforum.com Network Management Forum The Network Management Forum (NMF) was established in 1989 with the objectiveto speed progress in the development of standardized ‘umbrella’ network management systems. The members are drawn broadly from two camps, major network operators (e.g. British Telecom, which played a leading role in the initial establishment of the forumand provided first the president) and computermanufacturers DEC, (e.g. Hewlett Packard,IBM,SUN, etc.).Valuable outputs of the N M F have been the OMNIpoint and SPIRIT (service providers integrated requirements for information technology)specifications.The OMNIpoint specifications were thefirst attemptto consolidatethemanyemergingcomputerandnetworkmanagementstandardsand specifications into a meaningful and realizable whole. Address Network Management Forum (NMF) 1201 Mount Kemble Avenue Morristown New Jersey NJ 07960 United States of America Tel: (1) 201 425 1900 A T M Forum The ATM Forum came about through the interest of four major manufacturers who wanted to speed up the standardization process of ATM. It was set up in October 1991 by Northern Telecom(nowcalledNortel),Sprint,SunMicrosystems and Digital Equipment Corporation (DEC). In January 1992 membership was opened to wider participation from the telecommunication industry. The purpose of the ATM forum is to promote the development of technical standards for ATM and to raise awareness in the market of its capabilities. Many ATM standards adopted by ITU-T are heavily based on (if not identical to) those previously issued by the ATM forum. Address The ATM Forum 2570 West El Camino Real Suite 304
736 TECHNICAL STANDARDS FOR NETWORKS Mountain View California CA 94040 United States of America Tel: (1) 415 949 6700 info@atmforum.com Internet Engineering Task Force (IETF) The IETF is the group which develops the technical standards (RFCs (requests for comment)) for the Internet. The RFCs themselves can be obtained from Jon Poste1 RFC Editor USC Information Sciences Institute 4676 Admiralty Way Marina del Rey CA 90292-6695 United States of America Tel: (1) 213 822 1511 postel@isi.edu RFCs may also be viewed using FTP on the host nisc.sri.com 40.6 PROPRIETARY STANDARDS Despite the phenomenal number of standards organizations around theworld, a few of whichhavebeenmentioned,somecompaniesnonetheless feel that they can steala march on their competitors by developing their own proprietary (as opposed to open) technical standards. By proprietary we mean that the standards are not available for free use by any manufacturer;either they may not be published at all, or alternatively a ‘licence fee’ is demanded when the standards are used in the design of new equipment. It is usuallyonlylarge and powerfulorganizationswhocanaffordtoretaintheir standards as proprietary. The markets that such companies can command for their proprietary technology make it worthwhile to protect technical the rights. Other companies may find it lucrative to ‘buy-into’ these standards, so that they in turn may sell compatible ‘add-on’ equipment, but the lead company retains an edge. Examples of companies who have been successful in retaining control of proprietary standards are AT&T and IBM. American Telephone and Telegraph Company ( A T & T ) One of the world’s largest telecommunications carriers (based in the United States), AT&T and the new equipment manufacturer, Lucent, which was created by spin-off fromAT&T, draw technical their strengthfrom famous their research arm, Bell Laboratories. Anexample of one of AT&T’s proprietarystandards is the UNIX operating system, used as the operating software in many modern computer systems.
PROPRIETARY STANDARDS 737 Address Lucent Technologies Customer Information Centre 2855 North Franklin Road Indianapolis Indiana 46219 United States of America Tel: (1)-800-432-6600 (1)-888-582-3688 Bell Communications Research (Bellcore) Bellcore is the jointly owned research arm of the seven United States Regional Bell Operating Companies (RBOCs). It was formed partly with staff from AT&T’sBell Laboratories at the time of AT&T divestiture in the mid-1980s. Bellcore initially gained considerable respect for its networking standards called Technical References ( T R s ) , in particular in the field of intelligent networks and services (Chapter 11). Preliminary versions of TRsare called TAs (TechnicalAdvisories). In recentyears,however, Bellcore has suffered from a lack of clear direction and funding from its owners, who see themselves increasingly in competition with one another. Address Customer Service, Technical Publications Bellcore 444 Hoes Lane Piscataway New Jersey 08854 United States of America Tel: (1)-908-758-2142 British Telecom ( B T ) BT is thelargestpublictelecommunications operator in the United Kingdom. It is descended from the state-owned Post Ofice Telecommunications (formerly known as GPO (GeneralPost Ofice)). BritishTelecomremainsa predominant force in UK network standards setting. The standards are nowadays catalogued as British Telecom NetworkRequirements (or BTNRs). Examplesinclude BTNR 190 ( D P N S S , Digital Private Network Signalling System, a widely used standard in private networking of PBXs). Address British Telecom Network Secretariat Postpoint 2C07 403 Saint John Street London EClV 4PL United Kingdom Tel: (44) 171 843 51 88
738 NETWORKS FOR STANDARDS TECHNICAL International Business Machines (IBM) Perhaps the world’s most important computer manufacturer, it was IBM who gave us thestandardhardwareandbusconfigurationformanymainframeandpersonal computers and the systems network architecture ( S N A ) to communicate data between interconnected computers. UK Address IBM Technical Publication Centre Alencon House Alencon Link Basingstoke Hampshire RG21 7EJ United Kingdom Tel: (44) 1256 478166 European Address IBM Software Manufacturing Solutions IBM Denmark A/S Sortemosevej 2 1 Alleroed DK 3450 Denmark Tel: (45) 2 33 000 United States Address IBM Mechanicsburg Distribution Centre 180 Kost Road Mechanicsburg Pennsylvania PA 17055-0786 United States of America Tel: (1)-717-796-3200 (1)-800-879-2755tpb -1 40.7 THESTRUCTUREAND CONTENT OF ITU-T RECOMMENDATIONS Finally, we takealookintothestructureandcontent of the recommendations of the world’sleading authority networking on standards, ITU-T. ITU-T the The recommendations used to be approved every four years (at CCITT plenary assemblies of all thememberorganizations).Thisused to be theculminationoffouryears development work, establishing new recommendations, improving existing, and deletingobsolete ones. recommendations then The were published in aseries of coloured volumes, a process taking an entire year because all the transcripts had to be translatedand publishedinalltheworkinglanguages.Each four yearly issue was
THE STRUCTURE AND CONTENT OF ITU-T RECOMMENDATIONS 739 given a‘colour’ which wasassigned to each of the bound volumesinwhichthe recommendationsappeared, and every four yearswitheachsubsequent issue the colour was changed. The whole set of volumescorresponding to aparticularyear thus became colloquially known as The Blue Book (1988), or The Red Book (1984). Thus e the yellow book was approved in 1980 e the red book was approved in 1984 e the blue book was approved in 1988 Table 40.2 ITU-T seriesof recommendations Recommendation series Subject coverage A Organization of the work of the ITU-T B Means of expression (symbols, terms, vocabulary, etc.) C General telecommunications statistics D Recommendations for general application, including general tariff principles and charging and accounting in international telecommunication services and recommendations for regional application E International telephone network and ISDN: operation, numbering routing, mobile services, quality of service, network management and traffic engineering F Operations and quality of service: telegraph services, mobile service, telematic service, message handling services, directory services, document communication, data transmission services, audiovisual services, ISDN services, universal personal telecommunication, human factors G Transmission systems and media H Transmission of non-telephone signals i Integrated services digital network (ISDN) J Transmission of sound-programme and television signals K Protection against interference L Construction, installation and protection of cables and other elements of outside plant M Maintenance and telecommunications management network (TMN) N Maintenance of international sound-programme and television transmission circuits 0 Specifications for measuring equipment P Telephone transmission quality Q General recommendations on telephone switching and signalling R Telegraphy S Alphabetical telegraph terminal equipment T Telematic services U Telegraph switching V Data communication over the telephone network X Public data networks Z Programming languages (including SDL, specification and description language; CHILL, CCITT high level language; and MML, man-machine language)
740 TECHNICAL STANDARDS FOR NETWORKS The four year cycle of issueing new recommendations was ended in 1992, when the plenary assembly restructured the ITU. One of the objectives of the re-organization of the CCITT into the ITU-T to speed up the process of agreement and publication of was standards. Thus itbecamepossible to issue new recommendations as soonas they becameavailable. Therecommendations issued since 1992 havethereforeappeared individually as separate recommendations on plain white paper. Colloquially these are known as the white book. Each updated recommendation is an improvement over its predecessor, but there is no guarantee of compatibility between equipments which have been designed to differ- ent versions of the same recommendation. Thus, for example, there no guarantee that is themessage handling system (MHS) of theX.400recommendation of 1988 was compatible with the version of 1984 (and indeed it was not), One of theproblems of the new publishing regime is that the overview of the standards has to some extent been lost. Each book of recommendations used to be generally cohesive and compatible within itself. Nowadays, it is difficult to obtain a full picture of all the otherrelevant recommendations, because some of these may not yet be fully complete and thus published. Table 40.2 provides an overview of the subject areas, covered by the various series of recommendations, which make up each book. Recommendations are usually known by their series letter and a number; X.25 for example is a particular type of datu com- munications network interface in the X-series of recommendations, in fact the one used in packet switched networks.

CÓ THỂ BẠN MUỐN DOWNLOAD