ISO/IEC 8825-2:2021
(Main)Information technology — ASN.1 encoding rules — Part 2: Specification of Packed Encoding Rules (PER)
Information technology — ASN.1 encoding rules — Part 2: Specification of Packed Encoding Rules (PER)
This document specifies a set of Packed Encoding Rules that may be used to derive a transfer syntax for values of types defined in Rec. ITU-T X.680 | ISO/IEC 8824-1. These Packed Encoding Rules are also to be applied for decoding such a transfer syntax in order to identify the data values being transferred. The encoding rules specified in this document : – are used at the time of communication; – are intended for use in circumstances where minimizing the size of the representation of values is the major concern in the choice of encoding rules; – allow the extension of an abstract syntax by addition of extra values, preserving the encodings of the existing values, for all forms of extension described in Rec. ITU-T X.680 | ISO/IEC 8824‑1; – can be modified in accordance with the provisions of Rec. ITU-T X.695 | ISO/IEC 8825‑6.
Technologies de l'information — Règles de codage ASN.1 — Partie 2: Spécification des règles de codage compact (PER)
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INTERNATIONAL ISO/IEC
STANDARD 8825-2
Sixth edition
2021-06
Information technology — ASN.1
encoding rules —
Part 2:
Specification of Packed Encoding
Rules (PER)
Technologies de l'information — Règles de codage ASN.1 —
Partie 2: Spécification des règles de codage compact (PER)
Reference number
©
ISO/IEC 2021
© ISO/IEC 2021
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ii © ISO/IEC 2021 – All rights reserved
Foreword
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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.691 (02/2021).
This sixth edition cancels and replaces the fifth edition (ISO/IEC 8825-2:2015), which has been
technically revised. It also incorporates ISO/IEC 8825-2:2015/Cor 1:2017.
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
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© ISO/IEC 2021 – All rights reserved iii
CONTENTS
Page
Introduction . vi
1 Scope . 1
2 Normative references . 1
2.1 Identical Recommendations | International Standards . 1
2.2 Additional references . 1
3 Definitions . 2
3.1 Specification of Basic Notation . 2
3.2 Information Object Specification . 2
3.3 Constraint Specification . 2
3.4 Parameterization of ASN.1 Specification . 2
3.5 Basic Encoding Rules . 2
3.6 PER Encoding Instructions . 2
3.7 Additional definitions . 2
4 Abbreviations . 5
5 Notation . 5
6 Convention . 5
7 Encoding rules defined in this Recommendation | International Standard . 5
8 Conformance . 6
9 PER encoding instructions . 6
10 The approach to encoding used for PER . 7
10.1 Use of the type notation . 7
10.2 Use of tags to provide a canonical order . 7
10.3 PER-visible constraints . 7
10.4 Type and value model used for encoding . 9
10.5 Structure of an encoding . 9
10.6 Types to be encoded . 10
11 Encoding procedures . 10
11.1 Production of the complete encoding . 10
11.2 Open type fields . 11
11.3 Encoding as a non-negative-binary-integer . 11
11.4 Encoding as a 2's-complement-binary-integer . 12
11.5 Encoding of a constrained whole number . 12
11.6 Encoding of a normally small non-negative whole number . 13
11.7 Encoding of a semi-constrained whole number . 13
11.8 Encoding of an unconstrained whole number . 13
11.9 General rules for encoding a length determinant . 14
12 Encoding the boolean type . 16
13 Encoding the integer type . 16
14 Encoding the enumerated type . 17
15 Encoding the real type . 18
16 Encoding the bitstring type . 18
17 Encoding the octetstring type . 19
18 Encoding the null type . 19
19 Encoding the sequence type . 19
20 Encoding the sequence-of type . 20
21 Encoding the set type . 21
22 Encoding the set-of type . 21
23 Encoding the choice type. 21
Rec. ITU-T X.691 (02/2021) iii
© ISO/IEC 2021 – All rights reserved
24 Encoding the object identifier type . 22
25 Encoding the relative object identifier type . 22
26 Encoding the internationalized resource reference type . 22
27 Encoding the relative internationalized resource reference type . 23
28 Encoding the embedded-pdv type . 23
29 Encoding of a value of the external type . 23
30 Encoding the restricted character string types . 24
31 Encoding the unrestricted character string type . 26
32 Encoding the time type, the useful time types, the defined time types and the additional time types . 26
32.1 General . 26
32.2 Encoding subtypes with the "Basic=Date" property setting . 30
32.3 Encoding subtypes with the "Basic=Time" property setting . 32
32.4 Encoding subtypes with the "Basic=Date-Time" property setting . 35
32.5 Encoding subtypes with the "Basic=Interval Interval-type=SE" property setting . 35
32.6 Encoding subtypes with the "Basic=Interval Interval-type=D" property setting . 36
32.7 Encoding subtypes with the "Basic=Interval Interval-type=SD" or
"Basic=Interval Interval-type=DE" property setting . 37
32.8 Encoding subtypes with the "Basic=Rec-Interval Interval-type=SE"
property setting. 38
32.9 Encoding subtypes with the "Basic=Rec-Interval Interval-type=D" property setting . 38
32.10 Encoding subtypes with the "Basic=Rec-Interval Interval-type=SD" or
"Basic=Rec-Interval Interval-type=DE" property setting . 39
32.11 Encoding subtypes with mixed settings of the Basic property . 40
33 Object identifiers for transfer syntaxes . 42
Annex A – Example of encodings . 43
A.1 Record that does not use subtype constraints . 43
A.1.1 ASN.1 description of the record structu
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