1、BRITISH STANDARD BS EN 61334-6:2001 IEC 61334-6:2000 Distribution automation using distribution line carrier systems Part 6: A-XDR encoding rule The European Standard EN 61334-6:2000 has the status of a British Standard ICS 29.240.99; 33.040.40 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED B
2、Y COPYRIGHT LAWBS EN 61334-6:2001 This British Standard, having been prepared under the direction of the Electrotechnical Sector Committee, was published under the authority of the Standards Committee and comes into effect on 15 June 2001 BSI 06-2001 ISBN 0 580 37387 8 National foreword This British
3、 Standard is the official English language version of EN 61334- 6:2000. It is identical with IEC 61334-6:2000. The UK participation in its preparation was entrusted to Technical Committee PEL/57, Power system control and associated communications, which has the responsibility to: A list of organizat
4、ions represented on this committee can be obtained on request to its secretary. From 1 January 1997, all IEC publications have the number 60000 added to the old number. For instance, IEC 27-1 has been renumbered as IEC 60027-1. For a period of time during the change over from one numbering system to
5、 the other, publications may contain identifiers from both systems. Cross-references Attention is drawn to the fact that CEN and CENELEC Standards normally include an annex which lists normative references to international publications with their corresponding European publications. The British Stan
6、dards which implement these international or European publications may be found in the BSI Standards Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to
7、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 from legal obligations. aid enquirers to understand the text; present to the responsible international/E
8、uropean committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the EN title page,
9、 pages 2 to 39 and a back cover. The BSI copyright date displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. Date Comments(8523($167$1$5 (1 1250(8523e(11( (8523b,65HQFRGLQJUXOH ,(5 5 provide optimal 4)encoding for DLMS PDUs. NOTE Provid
10、ed that A-XDR ensures optimal encoding for DLMS PDUs, it is intended to be the default encoding rule for DLMS-based communication protocols. Nevertheless, the default and also the possibly usable optional encoding rules will be specified in the Application Layer document of the given protocol (for e
11、xample, IEC 61334-4-42), as part of the Application context. 2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this part of IEC 61334. For dated references, subsequent amendments to, or revisions of, any of the
12、se publications do not apply. However, parties to agreements based on this part of IEC 61334 are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to
13、 applies. Members of ISO and IEC maintain registers of currently valid International Standards. IEC 61334-4-41:1996, Distribution automation using distribution line carrier systems Part 4: Data communication protocols Section 41: Application protocols Distribution line message specification IEC 6133
14、4-4-42:1996, Distribution automation using distribution line carrier systems Part 4: Data communication protocols Section 42: Application protocols Application layer ISO/IEC 8825-2:1997, Information technology ASN.1 Encoding rules: Specification of packed encoding rules (PER) ITU-T Recommendation X.
15、208:1988, Specification of Abstract Syntax Notation One (ASN.1) ITU-T Recommendation X.209:1988, Specification of basic encoding rules for Abstract Syntax Notation One (ASN.1) 3)A-XDR stands for Adapted XDR. In fact, these encoding rules are derived from a proven and de facto standard of the Unix wo
16、rld, called XDR (eXternal Data Representation, rfc1014). 4)See footnote 2 of the introduction. Page5 BSEN613346:2000 BSI 06-2001 3 General characteristics of A-XDR A-XDR specifies encoding rules which can be used to encode and decode the values of an abstract syntax defined as the values of a single
17、 ASN.1 type (the outermost type). This single ASN.1 type is either a simple type or a composite type. A component of a composite type may be a simple type or a composite type itself. The A-XDR encoding rules exploit the fact that the sender and the receiver of a DLMS PDU are operating exactly the sa
18、me specification of the abstract syntax. While with BER the encoding of every value of any type of abstract syntax is constructed in type-length-value (TLV) style, A-XDR encodes the type and the length of the value only when this information is necessary. This implies that without knowledge of the t
19、ype of value encoded it is not possible to determine the structure of the encoding. NOTE This encoding method gives the result that A-XDR encoding rules are not extensible (see annex A). In order to keep A-XDR as simple as possible, some restrictions apply with respect to the abstract syntax to be e
20、ncoded as follows: no encoding support is provided for ASN.1 types which are not used in DLMS 5) ; the CHOICE ASN.1 type should contain only explicitly 6)tagged components. A-XDR specifies byte-oriented encoding rules. This means that each part of the encoding and therefore also the encoding of the
21、whole is an integral number of bytes. 4 Structure of an encoding The basis of BER encoding (see ITU-T Recommendation X.209) is a structure, made up of three parts: type, length and value, as shown in figure 1. In BER, these three parts are termed identifier (I), length (L) and contents (C). The iden
22、tifier part identifies the type, the length part allows the end of the contents 7)to be found, and the contents part conveys one of the possible values of that type. Identifier Length Contents Figure 1 The basic BER structure The contents field can be simply a series of bytes 8)(primitive encoding)
23、or a series of nested encoding (constructed encoding), as shown in figure 2. 5) Annex B enumerates the ASN.1 types and keywords which are used in the DLMS specification. 6) The terms “explicit tagging“ and “implicit tagging“ have a slightly different meaning in A-XDR than that specified for ASN.1 an
24、d BER. Subclause 6.7 deals with these notions and also introduces the new “ASN.1 explicit tagging“ term. 7) In fact, for BER, the length field does not always literally represent the length of the contents. BER specifies two forms (definite and indefinite) of the length field. Although, when the def
25、inite form is used, the length field effectively represents the number of bytes in the contents field, for the indefinite form the length field indicates that the contents are terminated by end-of-contents bytes. 8) Zero or more. IEC 730/2000 Page6 BSEN613346:2000 BSI 06-2001 I1 L1 I2 L2 I3 L3 C3 I4
26、 L4 C4 I5 L5 C5 I6 L6 C6 C2 C1 Figure 2 The structure of a constructed BER encoding The nesting can be as deep as needed and stops either with a primitive encoding or with a constructed encoding with empty contents. A-XDR is based upon the same encoding structure, but in order to benefit from the fa
27、ct that the sender and the receiver of a DLMS PDU are operating exactly the same specification of the abstract syntax, A-XDR does not encode the Identifier (I) and/or the Length (L) fields when those fields convey redundant information (when not to encode one or both of these fields does not result in uninterpretable, ambiguous encoding). A constructed A-XDR encoding therefore results in a structure as shown in figure 3. I1 L1 L2 C3 I4 L4 C4 L5 C5 C6 L7 C7 C8 I9 L9 C9 C2 C1 Figure 3 The structure of a constructed A-XDR encoding IEC 731/2000 IEC 732/2000 Page7 BSEN613346:2000
