1、BRITISH STANDARD BS4505-1: 1981 ISO1745-1975 Digital data transmission Part 1: Specification for basic mode control procedures ISO title: Information processing Basic mode control procedures for data communication systems UDC681.327.8BS4505-1:1981 This British Standard, having been prepared under th
2、e directionof the Data Processing Standards Committee, was published under the authority ofthe Board ofBSI and comes intoeffect on November1981 BSI 04-1999 First published September 1969 First revision November 198 The followingBSI references relate to the work on this standard: Committee reference
3、OIS/6 Draft for comment81/60118DC ISBN 0 580 12371 5 Cooperating organizations The Data Processing Standards Committee, under whose direction this British Standard was prepared, consists of representatives from the following: British Computer Society Ltd.* British Paper and Board Industry Federation
4、 (PIF) British Printing Industries Federation Business Equipment Trade Association* Central Computer and Telecommunications Agency (Civil Service Department)* Committee of London Clearing Bankers on behalf of the Committee of Scottish Clearing Bankers, Co-operative Bank, Central Trustee Savings Bank
5、 and Yorkshire Bank* Department of Industry (Computers, Systems and Electronics) Department of Industry (National Physical Laboratory)* Electricity Supply Industry in England and Wales* Government Communications Headquarters HM Customs and Excise Institute of Cost and Management Accountants Institut
6、e of Purchasing and Supply Institution of Electrical Engineers Inter-university Committee on Computing London Transport Executive National Computer Users Forum National Computing Centre Ltd.* National Research Development Corporation Post Office* Society of British Aerospace Companies Limited The or
7、ganizations marked with an asterisk in the above list, together with the following, were directly represented on the Technical Committee entrusted with the preparation of this British Standard: British Airways British Electrical and Allied Manufacturers Association (BEAMA) British Gas Corporation Br
8、itish Railways Board Business Equipment Trade Association Civil Aviation Authority Engineering Equipment Users Association Ministry of Defence Telecommunication Engineering and Manufacturing Association (TEMA) Amendments issued since publication Amd. No. Date of issue CommentsBS4505-1:1981 BSI 04-19
9、99 i Contents Page Cooperating organizations Inside front cover National foreword ii 0 Introduction 1 1 Scope and field of application 2 2 Definitions of the transmission control characters 3 3 Message formats 4 4 Description of phases 6 5 Description of use of the transmission control characters 12
10、 Annex A Definitions 17 Annex B Extensions of transmission control functions using DLE sequences 19 Annex C Alternative positive acknowledgement option 19 Figure 1 Phase linkage diagram 8 Figure 2 Phase 2 Establishment of data link 10 Figure 3 Phase 3 Information transfer 13 Figure 4 Phase 4 Termina
11、tion 14 Table of phases 2 Publications referred to Inside back coverBS4505-1:1981 ii BSI 04-1999 National foreword This British Standard, prepared under the direction of the Data Processing Standards Committee, is identical with ISO1745-1975 “Information processing Basic mode control procedures for
12、data communication systems” published by the International Organization for Standardization (ISO). This British Standard supersedes BS4505-1:1969 which is now withdrawn. Terminology and conventions. The text of the international standard has been approved as suitable for publication as a British Sta
13、ndard without deviation. Some terminology and certain conventions are not identical with those used in British Standards; attention is especially drawn to the following. Wherever the words “International Standard” appear, referring to this standard, they should be read as “British Standard”. A relat
14、ed British Standard for ISO1177-1973 is BS4505 “Digital data transmission” Part 2:1969 “Character structure for start/stop and synchronous transmission”. It refers to the United Kingdom7-bit data code rather than the ISO7-bit code. A related British Standard for ISO2111-1972 is BS4505-4:1971 “Basic
15、mode control procedures code independent information transfer”. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity f
16、rom legal obligation. Cross references International standard Corresponding British Standard ISO646-1973 BS4730:1974 Specification for the United Kingdom7-bit data code (ISO-7-UK) (Technically equivalent) a ISO1155-1973 BS4505 Digital data transmission Part 3:1981 Method for use of longitudinal pari
17、ty to detect errors in information messages (Identical) ISO2382 BS3527 Glossary of terms used in data processing (Identical) BS4505 Digital data transmission ISO2628-1973 Part 6:1976 Complements to the basic mode control procedures; recovery, abort and interrupt, multiple station selection (Technica
18、lly equivalent) ISO2629-1973 Part 7:1976 Basic mode control procedures; conversational information message transfer (Technically equivalent) a BS4730 contains the basic code table and the International Reference Version of the ISO7-bit data code in addition to the United Kingdom7-bit data code. Summ
19、ary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 20, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on theinside fro
20、nt cover.BS4505-1:1981 BSI 04-1999 1 0 Introduction 0.1 General A data communication system may be considered as the ensemble of the terminal installations and the interconnecting network that permits information to be exchanged. A data link concept is identifiable when considering terminal installa
21、tions connected to the same network, operating at the same speed, in the same code. Whenever actions on the respective transmission control characters take place, a separation of data links is constituted. Typical examples where this applies are: store and forward switching centres, concentrators, i
22、ntermediate reformatting and speed-change devices. The information transfer in a data link is monitored by data link control procedures where some characters, selected within a code set, are given particular meanings according to the transmission phase and are used for various purposes such as to de
23、lineate information, to reverse the direction of transmission, to ask questions, to answer, etc. The data link control procedures are categorized in classes which are referred to as modes of operation. The present considerations relate to one class called “basic mode”, which is defined as follows: I
24、n the basic mode all the necessary transmission control information (for example, message framing and supervisory instructions) passing from one station to another is carried over the link by discrete control characters selected from the ten transmission control characters which are defined in the I
25、SO/CCITT7-bit code (ISO646). The information exchanges are carried out in the alternate mode on standard communication facilities. The control of the data link is not affected by any characters other than the ten transmission control characters. Other codes than the ISO/CCITT code may therefore be t
26、ransmitted provided that they do not contain any of the ten transmission control characters in either heading or text. Sequences of transmission control character combinations such as DLE.XXX are not permitted, with the one exception DLE.EOT which is defined as “Disconnect”. Extensions to the basic
27、mode are contained in the following International Standards: ISO2111, Basic mode control procedures Code independent information transfer; ISO2628, Basic mode control procedures Complements; ISO2629, Basic mode control procedures Conversational information message transfer; and also in Annex B and A
28、nnex C of this International Standard. The following considerations have been taken into account in developing the rules for the basic mode: The rules are based on the assumption that one of the stations in each connection would be either a computer or a device capable of handling automatically an e
29、xchange of information. The rules are designed to allow the complexity of operation to be increased from a basic level by adding options. These options are designed so that any number of stations can still communicate even though they normally operate at different levels of complexity. It is desirab
30、le to reduce optional features in this International Standard to a minimum, but still retain a balance between an economic solution for the “low cost systems” and extendability for encompassing more complex systems. The rules may be difficult to implement in very simple systems involving low cost de
31、vices and human control. On the other hand, in complex high speed computer links, the rules may seriously restrict the throughput of information. These two cases are regarded as the upper and lower fringes of the present International Standard and may be the subject of future International Standards
32、. With the above considerations, typical limitations of basic mode control procedures are: restriction of efficiency by the time delay which is due to the alternate mode of operation; single link operation only. 0.2 Communication phases The table below shows the various possible phases and sub-phase
33、s of a data communication. Phases1 and5, which relate to the establishment and clearing of connections over the general switched network, are under the responsibility of the CCITT and are therefore not covered by this International Standard. In each phase, one of the stations directs the operation a
34、nd is responsible for the continuity of the communication. The other station or stations only react to the actions of the responsible station. The transmission control characters which are shown alongside the various sub-phases are those which are involved in the basic mode of operation. EOT is show
35、n in parentheses in Phases2 and3 because its use within the phases initiates a changeover to Phase4.BS4505-1:1981 2 BSI 04-1999 1 Scope and field of application 1.1 General This International Standard specifies the method of implementation of the ISO/CCITT7-bit coded character set 1)for information
36、interchange on data transmission channels. It also defines the formats of the transmitted messages and the supervisory sequences which are part of the transmission control procedures. It covers the majority of existing data transmission systems and data link configurations used in conjunction with d
37、ata processing systems. These control procedures deal with transmission over one link at a time and do not describe the operation of data links in “tandem”. They relate to the class of control procedures which is known as the basic mode and apply at the interface between data communication equipment
38、 and data terminal equipment. Table of phases 1) See ISO646. CCITT: Alphabet No.5. Phase Function Stations name Transmission control characters Notes used in basic mode Action Responsible Forward Reaction Responsive Backward 1 Establishment of connection over general network a) Switching CCITT Respo
39、nsibility b) Identification 2 Establishment of data link a) Switching Call Calling Not covered at present Answer Called b) Polling Poll Control (EOT), ENQ Reply Tributary (EOT) c) Selecting Select Master (EOT), ENQ Reply Slave ACK, NAK 3 Information transfer Transfer Master SOH, STX Slave ETB, ETX,
40、Supervision (EOT) ACK, NAK, (EOT) 4 Termination a) Return to neutral state Terminate Master EOT Interrupt Slave EOT b) Return to control station Terminate Master EOT Interrupt Slave EOT c) Disconnect Disconnect Master DLE, EOT Disconnect Slave DLE, EOT 5 Clearing of connection CCITT ResponsibilityBS
41、4505-1:1981 BSI 04-1999 3 It is accepted that, in their present form, the control procedures are a framework upon which a system can be built and that, before the successful interconnection of equipment from different supplies can be ensured, it will be necessary to define additional details, such a
42、s: structure of prefixes or addresses when used; “time-out” procedures and the recovery procedures which follow the various time-out conditions (see ISO2628). This International Standard must be considered in conjunction with the following ISO publications: 1) ISO1177, Information processing Charact
43、er structure for start/stop and synchronous transmission; 2) ISO1155, Information processing Use of longitudinal parity to detect errors in information messages. 1.2 Assumptions 1) The information to be transmitted will normally be coded in accordance with the7-bit ISO/CCITT code. 2) All transmissio
44、n control functions will be performed by the use of ten specific transmission control characters which are defined in this code as TC1 to TC10. 3) No recommendation is made regarding the technique used (hardware or software); the part of the terminal installation where the information messages and s
45、upervisory sequences are generated and recognized. 4) Transmission may be at any data transfer rate, either serial or parallel and either start/stop or synchronous. 5) Responses to an information message or a supervisory sequence may be either by turn around of the channel or by using another channe
46、l. 6) The basic mode control procedures are applicable to systems of varied complexity based on either-way transmission using: a) One-way transfer of information with alternate supervision on the same channel. b) One-way transfer of information with alternate supervision on a separate channel. c) Al
47、ternate two-way transfer of information with alternate supervision on the same channel. d) Alternate two-way transfer of information with alternate supervision on separate channels. 7) The following cases will be the subject of further study: a) One-way transfer of information with simultaneous supe
48、rvision. b) Alternate two-way transfer of information with simultaneous supervision. c) Two-way simultaneous transfer of information with alternate supervision. d) Two-way simultaneous transfer of information with simultaneous supervision. 2 Definitions of the transmission control characters The bas
49、ic definitions of the ten transmission control characters, as taken from ISO646, are listed below (see clause5 for description of use). (TC1) SOH Start of heading A transmission control character used as the first character of a heading of an information message. (TC2) STX Start of text A transmission control character which precedes a text and which is used to terminate a heading. (TC3) ETX End of text A transmission control character which terminates a text. (TC4) EOT End of transmission A transmission control character used to i
