1、UDC 621.396.44 : 654.195.21 + 621.397.132.122 : 654.1 97.21 0 British Standards Instihrtion. No part oi this publication may be photocopied or otherwise reproduced without the prior permission in writing of BSI British Standard Wideband cabled distribution systems Part 5. Recommendations for one-way
2、 and interactive data services Rseaux de distribution par cbles, large bande Partie 5. Recommendations pour les services de donnes fonctionnant en mode unidirectionnel et en mode dialogu Breitba ndvertei lera n lagen Teil 5. Empfehlungen fr einseitigen Datendienst und Dialogdatendienst British Stand
3、ards Institution BSI BS*b513: PART*5 87 m 1b24bb9 0071015 8 BS 6513 : Part 5 : 1987 Foreword m This Part of BS 6513 has been prepared under the direction of the Electronic Equipment Standards Committee. It is based on a draft provided by the Department of Trade and Industry. It forms Part 5 of a mul
4、tipart standard for wideband cabled distribution systems; the other Parts to date are as follows: Part 1. Glossary of terms Part 2. Methods of measurement Part 3. Specification for performance requirements for downstream television and f.m. sound radio signals upstream television Part 4. Specificati
5、on for performance requirements for Part 6. Specification for safety requirements The following subjects relative to this Part will be included as additional clauses or supplements at a later date: (a) cable system to videotex service protocols: a recommendation of suitable gateway protocols; (b) co
6、mpatibility of level 3 teletext with CEPT videotex; (c) the domestic digital bus (D2 B): definition of procedures to allow subscriber control of access to the wideband cabled system services; (d) security of transactional services: whether or not encryption should be employed and authentication of m
7、essages. Compliance with a British Standard does not of itself confer immunity from legal obligations. EI BS*b513: PART55 87 W Lb2Ybb OOLOLb T W -_ _ BS 6513 : Part 5 : 1987 Contents Foreword Committees responsible Recommendations Section one. General 1.1 Scope 1.2 Definitions and abbreviations 1.3
8、General recommendations, including safety Section two. Interfaces 2.1 Interconnection with external networks 2.2 Subscriber data interfaces Section three. Performance guidelines 3.1 Error rates O 3.2 Service levels Section four. Operation of specialist services 4.1 General 4.2 Videotex services 4.3
9、Teletex services Section five. Data subscriber addressing 5.1 Interim recommendations Appendices A Bibliography B Interchange circuits between data terminal equipment (DTE) and data circuit-terminating equipment (DCE) for asynchronous DTEs Page Back cover Inside front cover C Interchange circuits be
10、tween data terminal equipment (DTE) and data circuit-terminating 2 2 3 4 5 8 8 9 9 23 32 37 38 equipment (DCE) for synchronous DTEs D Definitions of interchange circuits E Recommended alpha-numeric keyboard and TTL interface Tables 1 Characteristics of preferred asynchronous 2 Cable/equipment interf
11、aces required for videotex 3 Prestel display attribute control codes 4 Recommended character set and Prestel coding interfaces for start-stop terminals Figures 1 General model of data circuits of wideband cabled distribution system 2 Major interfaces for a videotex service 3 Identification of possib
12、le delivery methods 4 Prestel transmission codes 5 Conversion from Prestel to teletext 6 Security and privacy considerations: options 7 PSDN access line extension to teletex terminals 8 Head end PABX links to teletex terminals 9 The IS0 reference model for OSI: functional layers 10 Teletex terminal
13、identification 11 Head end cable mail server supporting user terminals 12 Head end cable mail server supporting WCDS terminals 13 Teletex document containing cable mail call control information 14 DCE/DTE interface address on PSS 15 Packet structure 16 Protocol identity and format Page 39 40 41 6 11
14、 15 31 4 10 12 13 17 24 25 25 26 27 28 28 30 33 34 35 1 BSI BSgb513: PART*5 87 Lb24bb9 0091017 1 m BS 6513 : Part 5 : 1987 Recommendations. Section one Section one. General 1.1 Scope This Part of BS 651 3 gives guidance on the provision of one-way and interactive data services on wideband cabled dis
15、tribution systems. It includes recommendations for connection to external networks, subscriber interfaces and addressing, and protocols for videotex (including the use of level 1 teletext as a method of delivery) and teletex services. It also provides some guidance on performance targets. These reco
16、mmendations are not intended to apply to the operation of data services, e.g. teletext, where these form part of a broadcast television service the signals of which are transported transparently to the wideband cabled system subscriber. NOTE. The titles of the publications referred to in this standa
17、rd are listed on the inside back cover and in appendix A. 1.2 Definitions and abbreviations 1.2.1 Definitions For the purposes of this Part of BS 6513 the definitions given in BS 6513 : Part 1; BS 4727 : Part 3 : Group 04; BS 6568; IEC Publication 50 (60); CCITT Red book, vol. X.l : Terms and Defini
18、tions or the appropriate CCIR or CCITT document apply, together with the following. 1.2.1.1 cable mail service. An electronic mail service supported on a wideband cabled distribution system, capable of interworking with teletex terminals supported on wide area packet switched data networks and/or pu
19、blicly available message handling systems, external to the wideband cabled distribution system. NOTE. The terminals and protocols supported on the wideband cabled distribution system need not be teletex compatible. 1.2.1.2 cable mail server. A computer system, generally located at or connected to th
20、e head end of a wideband cabled distribution system providing a cable mail service, including translation between teletex and/or publicly available message handling system protocols and the protocols used on the wideband cabled distribution system. 1.2.2 Abbreviations For the purposes of this Part o
21、f BS 6513 the following designations and abbreviations apply. ASCI I American Standard Code BT/British Telecom British Telecommunications plc CCITT International Telegraph and Telephone Consultative Committee CENELEC European Committee for Electrotechnical Standardization for Information Interchange
22、 CEPT CUG D B DCE DNIC D RCS DTE EC I A5 IP IS0 LAN Level 1 teletext Level 3 teletext MCL M HS NSAP o/c os I PABX PAD PIN European Conference of Postal and Telecommunication Administrations Closed user group: a group of users of a videotex service who are permitted (by an I P) to have access to part
23、 of a database not available to other users Domestic digital bus: an interconnection for domestic or similar electronic equipment in accordance with BS 6552 . Data circuit-terminating equipment Data network identification code Dynamically redefinable character set: a feature of the display standard
24、CEPT T/CD 06-01 whereby the character display formats held in a display terminal can be redefined by the incoming data Data terminal equipment External computer: another computer system accessed from a videotex system via a gateway International alphabet No. 5: WITT Recommendation T50 Information pr
25、ovider: an organization which provides data on a videotex service International Organization for Standardization Local area network The 1984 UK teletext broadcasting service features and display standard in current use. This corresponds to the current Preste1 display standard (see figures 4 and 5) T
26、he full presentation layer syntax of the UK teletext system, known as World System Teletext. The presentation layer corresponds very closely to that of the CEPT videotex presentation layer syntax of CEPT T/CD 06-01, and is fully described in World system teletext and data broadcasting system: Techni
27、cal Specification* Mercury Communications Ltd Message handling system (s) Network service access point Open circuit Open systems interconnection Private automatic branch exchange Packet assembler/disassembler Personal identity number; the password, unique to each user, by which the user proves his i
28、dentity. It can often be alphabetic as well as numeric *Published by and obtainable from Department of Trade and Industry, Information Technology Division, Kingsgate House, 66-74 Victoria Street, London SW1 E 6SW. 2 PSDN Packet switched data network PSS Packet Switchstream service; the British Telec
29、ommunications packet switched network PSTN Public switched telephone network TTL Transistor - transistor logic VDU Visual display unit WCDS Wideband cabled distribution systemh 1.3 General recommendations, including safety 1.3.1 Environmental conditions 1.3.1.1 Equipment in the subscribers premises.
30、 Any equip- ment in the subscribers premises should be in accordance with the recommendations in this Part of BS 6513 over the following ranges of external conditions: . (a) external ambient temperature range off 5 OC to + 40 OC; (b) external relative humidity up to 85 %; (c) mains supply voltage va
31、riation of f 10 % of the declared value of the supply; (d) mains supply frequency variation of f 5 % of the declared value of the supply. The equipment should be designed and installed in such a way that it is in accordance throughout its planned life with the recommendations of this Part of BS 6513
32、. 1.3.1.2 Equipment external to the subscribers premises. Equipment for the provision of one-way and interactive data services external to the subscribers premises should be in accordance with the recommendations of this Part of BS 6513 over the following range of conditions: (a) ambient temperature
33、 range external to the equipment cabinet of - 10 OC to + 45 OC; (b) external relative humidity up to 95 %; (c) mains supply voltage variation of f 10 % of the declared value of the supply; (d) mains supply frequency variation of f 5 % of the declared value of the supply. The equipment should be desi
34、gned and installed in such a way that it is in accordance with the recommendations of this Part of BS 651 3 throughout the planned life of the wideband cabled distribution system. 1.3.2 Safety The requirements for the safety of equipment incorporated in a wideband cabled distribution system for the
35、provision of data services are set out in BS 6513 : Part 6. 3 BSI BS*bSL3: PART*S 87 m Lb24bb9 009LOL9 5 BS 6513 : Part 5 : 1987 Section two Section two. Interfaces 2.1 Interconnection with external networks 2.1.1 General To permit maximum flexibility and innovation, wideband cabled distribution sys
36、tem operators are allowed to interconnect systems by any method that they mutually agree, subject to conditions of their individual operating licences. Where a public packet switched network is used for such interconnection the following recommendations , are made. At present there exists, in the UK
37、, only one public packet switched network, that operated by British Telecommuni- cations plc. Therefore at this time it is possible to make recommendations for connection to that network only. When the requirements of any other similar network which may be constructed by, for instance, Mercury Commu
38、nications, or any other, not necessarily packet switched, data network, are known, this Part of BS 651 3 may be amended to include those requirements. This recommendation does not preclude the wideband system operator from choosing to provide interconnection for instance with another particular wide
39、band system by the use of, say, a dedicated leased data link or a circuit switched network. It is merely that for multiple inter- connection, packet switched technology in many cases will provide the most suitable arrangements. 2.1.2 British Telecommunications Packet SwitchStream service 2.1.2.1 int
40、erconnection recommendations. Where a wideband cabled distribution system is, for the purpose of data interconnection with other systems or services, connected to the British Telecommunications Packet SwitchStream service (PSS), the detail of the inter- connection will be the subject of an interconn
41、ect agreement, as required by the Telecommunications Act 1984, between the wideband cable operator and British Telecom. This agreemerit should be based on CCITT Recommendations. 2.1.2.2 Additional recommendations. It is further recommended that, although the transport of data and the connection of c
42、ircuits within the wideband cabled distribution system will depend on current design and intended application (see figure I), and therefore it is essential that this should remain in the prerogative of the system operator, for interconnection by public packet switched network one or more of the mean
43、s of wideband cabled system operation described in 2.1.2.3 to 2.1.2.5 should apply. 2.1.2.3 Application servers. Where wideband cabled distribution systems provide application servers for such services as teleshopping, etc., each application server should, where interconnection external to the wideb
44、and cabled system is required, connect with the public packet switched network on demand like a packet mode terminal. WCDS proprietary transport mechanism I- l I I I I I I I I I Two-way I data interface Customer I I Facility t Teletex server function Packet assembler/ disassembler I I I I I I I I I
45、Gateway I X.25 function packet switched network terminating Electronic Output to television I mail server I function I I I II I I r-i I II I I n.rn.4 A“ 1 LClliC“ “I I I Other Li SI i- i services L-J Figure 1. General model of data circuits of wideband cabled distribution system 4 PART *5- BS 6513 :
46、 Part 5 : 1987 Section two Communication between the server and the customer terminals should be by means appropriate to the data transport system of the wideband cabled distribution system and the service facilities offered 2.1.2.4 Packet mode terminais. Where a wideband cabled distribution system
47、offers a service to packet mode terminals it should provide data channels which extend the packet switched network terminals from the head end (or other interconnection point) interface through to a customer interface (see 2.2) for packet mode terminals operating in accordance with CCITT Recommendat
48、ion X25 (1.984) and/or as implemented by British Telecommunications. As required by the Telecommunications Act 1984, these terminals would be subject to approval to the standards for such terminals for direct attachment to the Packet Switchstream network. The means whereby the data channels are exte
49、nded remain the prerogative of the wideband cabled system operator. 2.1.2.5 Packet asembler/disassernbier. Where the wideband cabled system offers a service for start-stop mode terminals there should be provided a packet assembler/disassembler (PAD), associated with the interconnecting packet mode terminal, operating in accordance with CCITT Recommendations X3 and X29. The wideband cabled system should organize internal data circuits between the PAD and customers start-stop mode terminals operating in accordance with CCITT Recommendation X28 and
