ISO/IEC 8825-3:2021

INTERNATIONAL ISO/IEC
STANDARD 8825-3
Fourth edition
2021-06
Information technology — ASN.1
encoding rules —
Part 3:
Specification of Encoding Control
Notation (ECN)
Technologies de l'information — Règles de codage ASN.1 —
Partie 3: Spécification de la notation de contrôle de codage (ECN)
Reference number
ISO/IEC 8825-3:2021(E)
©
ISO/IEC 2021

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ISO/IEC 8825-3:2021(E)

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ii © ISO/IEC 2021 – All rights reserved

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ISO/IEC 8825-3:2021(E)
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are
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Attention is drawn to the possibility that some of the elements of this document may be the subject of
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see www.iso.org/iso/foreword.html. In the IEC, see www.iec.ch/understanding-standards.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 6, Telecommunications and information exchange between systems, in collaboration
with ITU-T. The identical text is published as ITU-T X.692 (02/2021).
This fourth edition cancels and replaces the third edition (ISO/IEC 8825-3:2015), which has been
technically revised.
A list of all parts in the ISO/IEC 8825 series can be found on the ISO and IEC websites.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html and www.iec.ch/national-
committees.

© ISO/IEC 2021 – All rights reserved iii

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ISO/IEC 8825-3:2021(E)
CONTENTS
Page
Introduction . x
1 Scope . 1
2 Normative references . 1
2.1 Identical Recommendations | International Standards . 1
2.2 Additional references . 2
3 Definitions . 2
3.1 ASN.1 definitions . 2
3.2 ECN-specific definitions . 2
4 Abbreviations . 5
5 Definition of ECN syntax . 5
6 Encoding conventions and notation . 5
7 The ECN character set . 5
8 ECN lexical items . 6
8.1 Encoding object references . 6
8.2 Encoding object set references . 6
8.3 Encoding class references . 6
8.4 Reserved word items . 7
8.5 Reserved encoding class name items . 7
8.6 Non-ECN item . 7
9 ECN Concepts . 7
9.1 Encoding Control Notation (ECN) specifications . 8
9.2 Encoding classes . 8
9.3 Encoding structures . 9
9.4 Encoding objects . 9
9.5 Encoding object sets . 9
9.6 Defining new encoding classes . 9
9.7 Defining encoding objects . 11
9.8 Differential encoding-decoding . 11
9.9 Encoders options in encodings . 12
9.10 Properties of encoding objects . 12
9.11 Parameterization . 12
9.12 Governors . 13
9.13 General aspects of encodings . 13
9.14 Identification of information elements . 13
9.15 Reference fields and determinants . 14
9.16 Replacement classes and structures . 14
9.17 Mapping abstract values onto fields of encoding structures . 15
9.18 Transforms and transform composites . 15
9.19 Contents of Encoding Definition Modules . 16
9.20 Contents of the Encoding Link Module . 17
9.21 Defining encodings for primitive encoding classes . 17
9.22 Application of encodings . 19
9.23 Combined encoding object set . 19
9.24 Application point . 19
9.25 Conditional encodings . 20
9.26 Other conditions for applying encodings . 20
9.27 Encoding control for the open type . 21
9.28 Changes to ASN.1 Recommendations | International Standards . 21
10 Identifying encoding classes, encoding objects, and encoding object sets . 21
11 Encoding ASN.1 types . 24
11.1 General . 24
© ISO/IEC 2021 – All rights reserved
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ISO/IEC 8825-3:2021(E)
11.2 Built-in encoding classes used for implicitly generated encoding structures . 24
11.3 Simplification and expansion of ASN.1 notation for encoding purposes . 25
11.4 The implicitly generated encoding structure . 27
12 The Encoding Link Module (ELM) . 27
12.1 Structure of the ELM . 28
12.2 Encoding types . 28
13 Application of encodings . 29
13.1 General . 29
13.2 The combined encoding object set and its application . 29
14 The Encoding Definition Module (EDM) . 31
15 The renames clause . 33
15.1 Explicitly generated and exported structures . 33
15.2 Name changes . 34
15.3 Specifying the region for name changes . 35
16 Encoding class assignments . 36
16.1 General . 36
16.2 Encoding structure definition . 39
16.3 Alternative encoding structure . 41
16.4 Repetition encoding structure . 41
16.5 Concatenation encoding structure . 42
17 Encoding object assignments . 42
17.1 General . 42
17.2 Encoding with a defined syntax . 43
17.3 Encoding with encoding object sets . 44
17.4 Encoding using value mappings . 44
17.5 Encoding an encoding structure . 45
17.6 Differential encoding-decoding . 47
17.7 Encoding options . 48
17.8 Non-ECN definition of encoding objects . 49
18 Encoding object set assignments . 49
18.1 General . 49
18.2 Built-in encoding object sets . 50
19 Mapping values . 51
19.1 General . 51
19.2 Mapping by explicit values . 52
19.3 Mapping by matching fields . 53
19.4 Mapping by #TRANSFORM encoding objects . 54
19.5 Mapping by abstract value ordering . 54
19.6 Mapping by value distribution . 56
19.7 Mapping integer values to bits . 57
20 Defining encoding objects using defined syntax . 58
21 Types used in defined syntax specification . 59
21.1 The Unit type . 59
21.2 The EncodingSpaceSize type . 59
21.3 The EncodingSpaceDetermination type . 60
21.4 The UnusedBitsDetermination type . 60
21.5 The OptionalityDetermination type . 61
21.6 The AlternativeDetermination type . 62
21.7 The RepetitionSpaceDetermination type . 62
21.8 The Justification type . 63
21.9 The Padding type . 64
21.10 The Pattern and Non-Null-Pattern types . 64
21.11 The RangeCondition type . 65
© ISO/IEC 2021 – All rights reserved
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ISO/IEC 8825-3:2021(E)
21.12 The Comparison type . 65
21.13 The SizeRangeCondition type . 66
21.14 The ReversalSpecification type . 66
21.15 The ResultSize type . 67
21.16 The HandleValueSet type . 67
21.17 The IntegerMapping type . 68
22 Commonly used encoding property groups . 68
22.1 Replacement specification . 68
22.1.1 Encoding properties, syntax and purpose . 68
22.1.2 Specification restrictions . 69
22.1.3 Encoder actions . 70
22.1.4 Decoder actions . 70
22.2 Pre-alignment and padding specification . 71
22.2.1 Encoding properties, syntax and purpose . 71
22.2.2 Specification constraints . 71
22.2.3 Encoder actions . 71
22.2.4 Decoder actions . 71
22.3 Start pointer specification . 72
22.3.1 Encoding properties, syntax and purpose . 72
22.3.2 Specification constraints . 72
22.3.3 Encoder actions . 72
22.3.4 Decoder actions . 72
22.4 Encoding space specification . 73
22.4.1 Encoding properties, syntax and purpose . 73
22.4.2 Specification restrictions . 73
22.4.3 Encoder actions . 74
22.4.4 Decoder actions . 74
22.5 Optionality determination . 75
22.5.1 Encoding properties, syntax and purpose . 75
22.5.2 Specification restrictions . 75
22.5.3 Encoder actions . 76
22.5.4 Decoder actions . 76
22.6 Alternative determination . 77
22.6.1 Encoding properties, syntax and purpose . 77
22.6.2 Specification restrictions . 77
22.6.3 Encoder actions . 77
22.6.4 Decoder actions . 78
22.7 Repetition space specification . 78
22.7.1 Encoding properties, syntax and purpose . 78
22.7.2 Specification constraints . 79
22.7.3 Encoder actions . 80
22.7.4 Decoder actions . 80
22.8 Value padding and justification . 81
22.8.1 Encoding properties, syntax, and purpose . 81
22.8.2 Specification restrictions . 82
22.8.3 Encoder actions . 82
22.8.4 Decoder actions . 83
22.9 Identification handle specification . 83
22.9.1 Encoding properties, syntax and purpose . 83
22.9.2 Specification constraints . 84
22.9.3 Encoders actions. 84
22.9.4 Decoders actions . 84
22.10 Concatenation specification . 84
22.10.1 Encoding properties, syntax and purpose . 84
22.10.2 Specification constraints . 85
22.10.3 Encoder actions . 85
22.10.4 Decoder actions . 85
22.11 Contained type encoding specification . 85
22.11.1 Encoding properties, syntax and purpose . 85
22.11.2 Encoder actions . 86
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ISO/IEC 8825-3:2021(E)
22.11.3 Decoder actions . 86
22.12 Bit reversal specification . 86
22.12.1 Encoding properties, syntax, and purpose . 86
22.12.2 Specific
...