Information technology — ASN.1 encoding rules — Part 3: Specification of Encoding Control Notation (ECN)

This document defines a notation for specifying encodings of ASN.1 types or of parts of types. It provides several mechanisms for such specification, including: – direct specification of the encoding using standardized notation; – specification of the encoding by reference to standardized encoding rules; – specification of the encoding of an ASN.1 type by reference to an encoding structure; – specification of the encoding using non-ECN notation. It also provides the means to link the specification of encodings to the type definitions to which they are to be applied. ECN does not currently provide any support for specifications using the OID internationalized resource identifier type or the relative OID internationalized resource identifier type (see Rec. ITU-T X.680 | ISO/IEC 8824-1), and these are not referred to further in this Standard.

Technologies de l'information — Règles de codage ASN.1 — Partie 3: Spécification de la notation de contrôle de codage (ECN)

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Published
Publication Date
29-Jun-2021
Current Stage
6060 - International Standard published
Start Date
30-Jun-2021
Completion Date
30-Jun-2021
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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)
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2021

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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

members of ISO or IEC participate in the development of International Standards through technical

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ISO and IEC technical committees collaborate in fields of mutual interest. Other international

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The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for

the different types of document should be noted. This document was drafted in accordance with

the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives or

www.iec.ch/members_experts/refdocs)

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights. Details

of any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents) or the IEC list of patent

declarations received (see patents.iec.ch).

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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

© ISO/IEC 2021 – All rights reserved
Rec. ITU-T X.692 (02/2021) v
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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
...

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