ISO/IEC 8825-6:2015

INTERNATIONAL ISO/IEC
STANDARD 8825-6
Third edition
2015-11-15


Information technology — ASN.1
encoding rules: Registration and
application of PER encoding instructions
Technologies de l'information — Règles de codage ASN.1:
Enregistrement et application des instructions de codage PER






Reference number
ISO/IEC 8825-6:2015(E)
©
ISO/IEC 2015

---------------------- Page: 1 ----------------------
ISO/IEC 8825-6:2015(E)
COPYRIGHT PROTECTED DOCUMENT


©  ISO/IEC 2015
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any
means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission.
Permission can be requested from either ISO at the address below or ISO’s member body in the country of the requester.
ISO copyright office
Case postale 56 x CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland

ii © ISO/IEC 2015 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/IEC 8825-6:2015(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 committees
established by the respective organization to deal with particular fields of technical activity. ISO and IEC
technical committees collaborate in fields of mutual interest. Other international organizations, governmental
and non-governmental, in liaison with ISO and IEC, also take part in the work. In the field of information
technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of the joint technical committee is to prepare International Standards. Draft International
Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as
an International Standard requires approval by at least 75 % of the national bodies casting a vote.
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.
This third edition cancels and replaces the second edition of ISO/IEC 8825-6:2008 which has been technically
revised.
ISO/IEC 8825-6 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.695 (08/2015).
© ISO/IEC 2015 – All rights reserved iii

---------------------- Page: 3 ----------------------
I n t e r n a t io na l Te lec o mm u n ica tio n U n i o n


X.695
ITU-T
(08/2015)
TELECOMMUNICATION
STANDARDIZATION SECTOR
OF ITU

SERIES X: DATA NETWORKS, OPEN SYSTEM
COMMUNICATIONS AND SECURITY
OSI networking and system aspects – Abstract Syntax
Notation One (ASN.1)


Information technology – ASN.1 encoding rules:
Registration and application of PER encoding
instructions

Recommendation ITU-T X.695

---------------------- Page: 4 ----------------------
ITU-T X-SERIES RECOMMENDATIONS
DATA NETWORKS, OPEN SYSTEM COMMUNICATIONS AND SECURITY

PUBLIC DATA NETWORKS
Services and facilities X.1–X.19
Interfaces X.20–X.49
Transmission, signalling and switching X.50–X.89
Network aspects X.90–X.149
Maintenance X.150–X.179
Administrative arrangements X.180–X.199
OPEN SYSTEMS INTERCONNECTION
Model and notation X.200–X.209
Service definitions X.210–X.219
Connection-mode protocol specifications X.220–X.229
Connectionless-mode protocol specifications X.230–X.239
PICS proformas X.240–X.259
Protocol Identification X.260–X.269
Security Protocols X.270–X.279
Layer Managed Objects X.280–X.289
Conformance testing X.290–X.299
INTERWORKING BETWEEN NETWORKS
General X.300–X.349
Satellite data transmission systems X.350–X.369
IP-based networks X.370–X.379
MESSAGE HANDLING SYSTEMS X.400–X.499
DIRECTORY X.500–X.599
OSI NETWORKING AND SYSTEM ASPECTS
Networking X.600–X.629
Efficiency X.630–X.639
Quality of service X.640–X.649
Naming, Addressing and Registration X.650–X.679
Abstract Syntax Notation One (ASN.1) X.680–X.699
OSI MANAGEMENT
Systems management framework and architecture X.700–X.709
Management communication service and protocol X.710–X.719
Structure of management information X.720–X.729
Management functions and ODMA functions X.730–X.799
SECURITY X.800–X.849
OSI APPLICATIONS
Commitment, concurrency and recovery X.850–X.859
Transaction processing X.860–X.879
Remote operations X.880–X.889
Generic applications of ASN.1 X.890–X.899
OPEN DISTRIBUTED PROCESSING X.900–X.999
INFORMATION AND NETWORK SECURITY X.1000–X.1099
SECURE APPLICATIONS AND SERVICES X.1100–X.1199
CYBERSPACE SECURITY X.1200–X.1299
SECURE APPLICATIONS AND SERVICES X.1300–X.1399
CYBERSECURITY INFORMATION EXCHANGE X.1500–X.1599
CLOUD COMPUTING SECURITY X.1600–X.1699

For further details, please refer to the list of ITU-T Recommendations.

---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO/IEC 8825-6
RECOMMENDATION ITU-T X.695
Information technology –
ASN.1 encoding rules:
Registration and application of PER encoding instructions



Summary
Recommendation ITU-T X.695 | ISO/IEC 8825-6 specifies the rules for applying PER encoding instructions using either
type prefixes or an encoding control section.
Encoding instructions are a means of modifying the encodings of ASN.1 types for some specified encoding rule (in this
case PER). They can be inserted in an ASN.1 specification in square brackets (much like a tag in the Basic Encoding Rules,
BER) immediately before the type that they affect (type prefixes), or they can be collected together at the end of an ASN.1
module (an encoding control section).
It also specifies the procedures for developing, registering and publishing new PER encoding instructions from time to
time.


History
*
Edition Recommendation Approval Study Group Unique ID
1.0 ITU-T X.695 2007-05-29 17 11.1002/1000/9112
2.0 ITU-T X.695 2008-11-13 17 11.1002/1000/9613
3.0 ITU-T X.695 2015-08-13 17 11.1002/1000/12488





____________________
*
To access the Recommendation, type the URL http://handle.itu.int/ in the address field of your web browser, followed by the
Recommendation's unique ID. For example, http://handle.itu.int/11.1002/1000/11830-en.
 Rec. ITU-T X.695 (08/2015) i

---------------------- Page: 6 ----------------------
FOREWORD
The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of
telecommunications, information and communication technologies (ICTs). The ITU Telecommunication
Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical,
operating and tariff questions and issuing Recommendations on them with a view to standardizing
telecommunications on a worldwide basis.
The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes
the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
In some areas of information technology which fall within ITU-T's purview, the necessary standards are
prepared on a collaborative basis with ISO and IEC.



NOTE
In this Recommendation, the expression "Administration" is used for conciseness to indicate both a
telecommunication administration and a recognized operating agency.
Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain
mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the
Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other
obligatory language such as "must" and the negative equivalents are used to express requirements. The use of
such words does not suggest that compliance with the Recommendation is required of any party.




INTELLECTUAL PROPERTY RIGHTS
ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve
the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or
applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of
the Recommendation development process.
As of the date of approval of this Recommendation, ITU had not received notice of intellectual property,
protected by patents, which may be required to implement this Recommendation. However, implementers are
cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB
patent database at http://www.itu.int/ITU-T/ipr/.



¤ ITU 2015
All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior
written permission of ITU.
ii Rec. ITU-T X.695 (08/2015)

---------------------- Page: 7 ----------------------
CONTENTS
Page
1 Scope . 1
2 Normative references. 1
2.1 Identical Recommendations | International Standards . 1
3 Definitions . 1
4 Abbreviations . 2
5 Notation . 2
6 Information to be provided to specify a PER encoding instruction . 2
7 Status of a PER EI proposal during the approval process . 3
8 Approval process . 3
9 Publication by the Registration Authority . 4
10 Restrictions on the use of PER Encoding Instructions . 4
11 Assigning a PER EI to an ASN.1 type using a type prefix . 4
12 Assigning a PER encoding instruction using an encoding control section . 5
12.1 The encoding instruction assignment list . 5
12.2 Identification of the targets for a PER encoding instruction using a target list . 5
12.2.1 General rules . 5
12.2.2 Target identification using an ASN.1 type reference and identifiers . 7
12.2.3 Target identification using a built-in type name . 8
12.2.4 Use of identifiers in context . 8
13 Multiple assignment of PER encoding instructions . 9
13.1 Order in which multiple assignments are considered . 9
13.2 Effect of assigning a negating encoding instruction . 9
13.3 Multiple assignment of PER encoding instructions . 9
Annex A − Example of the application of PER EIs using prefixed encoding instructions .11
Annex B − Example of the application of PER EIs using targeted encoding instructions .14
Annex C − Summary of the ASN.1 notation .16


 Rec. ITU-T X.695 (08/2015) iii

---------------------- Page: 8 ----------------------
Introduction
Rec. ITU-T X.680 | ISO/IEC 8824-1 makes syntactic provision for the application of encoding instructions to modify the
behaviour of a particular set of encoding rules, identified by an encoding reference (see Rec. ITU-T X.680 | ISO/IEC
8824-1).
Rec. ITU-T X.691 | ISO/IEC 8825-2 specifies the BASIC-PER and CANONICAL-PER encoding rules, each with two
variants: the ALIGNED variant and the UNALIGNED variant. The PER encoding instructions allow minor variations to
be made in parts of the UNALIGNED variant of a BASIC-PER and CANONICAL-PER encoding. They have no effect
on the ALIGNED variant of these encodings.
NOTE – The purpose of PER encoding instructions is to ease the task of producing an ASN.1 specification, which when encoded
by the UNALIGNED variant of a PER encoding produces bit-patterns that exactly match those of a legacy protocol. It is unusual
for the ALIGNED variant to be used for this purpose, and so for simplicity all PER encoding instructions have no effect on the
ALIGNED variant.
This Recommendation | International Standard specifies the use of type prefixes and encoding control sections (see
Rec. ITU-T X.680 | ISO/IEC 8824-1, 31.3 and clause 54) to associate one or more PER encoding instructions with an
ASN.1 type. Where an encoding instruction is associated with an ASN.1 type, specific clauses in Rec. ITU-T X.691 |
ISO/IEC 8825-2 are amended according to the specification of the encoding instruction. These mechanisms are similar
to those for the application of XER encoding instructions specified in Rec. ITU-T X.693 | ISO/IEC 8825-4.
This Recommendation | International Standard also specifies the procedures for the operation of a Registration Authority
to receive, record and publish the specification of PER encoding instructions that are agreed from time to time. The
Registration Authority is the ITU Telecommunication Standardization Bureau, and the form of publication is an
Implementers' Guide for ASN.1. This Guide will be available freely on an ITU-T web-site.
This Recommendation | International Standard also specifies the procedures to be used for the approval of new PER
encoding instructions. Broadly, these procedures involve the prior publication in the Implementers' Guide of a proposed
new encoding instruction, with a later publication announcing that the new encoding instruction has been approved by a
simple resolution of the relevant Study Group of ITU-T and the relevant Sub-Committee of ISO/IEC JTC 1.
Clauses 6 to 9 specify the operation of the Registration Authority for PER encoding instructions.
Clauses 10 to 13 specify the application of PER encoding instructions to an ASN.1 specification.
Annex A is informative and contains an example of the application of PER encoding instructions using encoding prefixes.
Annex B is informative and contains an example of the application of the same PER encoding instructions using an
encoding control section.
Annex C is informative and summarizes the productions defined in this Recommendation | International Standard.
iv Rec. ITU-T X.695 (08/2015)

---------------------- Page: 9 ----------------------
ISO/IEC 8825-6:2015 (E)
INTERNATIONAL STANDARD
ITU-T RECOMMENDATION
Information technology –
ASN.1 encoding rules:
Registration and application of PER encoding instructions
1 Scope
This Recommendation | International Standard:
a) specifies the information needed and the format to be used for specifying PER encoding instructions;
b) specifies the mechanisms for approving new PER encoding instructions from time to time and the
operation of the Registration Authority for PER encoding instructions;
c) specifies the means of associating a PER encoding instruction with an ASN.1 type using both type prefixes
and an encoding control section.
2 Normative references
The following Recommendations and International Standards contain provisions which, through reference in this text,
constitute provisions of this Recommendation | International Standard. At the time of publication, the editions indicated
were valid. All Recommendations and Standards are subject to revision, and parties to agreements based on this
Recommendation | International Standard are encouraged to investigate the possibility of applying the most recent edition
of the Recommendations and Standards listed below. Members of IEC and ISO maintain registers of currently valid
International Standards. The Telecommunication Standardization Bureau of the ITU maintains a list of currently valid
ITU-T Recommendations.
2.1 Identical Recommendations | International Standards
– Recommendation ITU-T X.680 (2015) | ISO/IEC 8824-1:2015, Information technology – Abstract Syntax
Notation One (ASN.1): Specification of basic notation.
– Recommendation ITU-T X.691 (2015) | ISO/IEC 8825-2:2015, Information technology – ASN.1 encoding
rules: Specification of Packed Encoding Rules (PER).
3 Definitions
For the purposes of this Recommendation | International Standard, the definitions of Rec. ITU-T X.680 | ISO/IEC 8824-1
apply. The following additional definitions apply.
3.1 associated encoding instructions (for a type): A set of PER encoding instructions associated with a type.
3.2 final encoding instructions (for a type): The set of PER encoding instructions associated with a type as a
result of the complete ASN.1 specification, and which are applied in producing encodings of that type.
3.3 identifying keyword: A word or hyphenated word that identifies a PER encoding instruction.
3.4 inherited encoding instructions: PER encoding instructions that are associated with the type identified by a
type reference.
3.5 Joint ITU-T | ISO/IEC JTC1 Collaborative Team for ASN.1: A group established in accordance with
Rec. ITU-T A.23, Annex A and ISO/IEC JTC 1 Directives Edition 5 Version 2.0, subclause 2.6.4 and Annex K, clause 8
to progress work on Joint Text in relation to Abstract Syntax Notation One (ASN.1).
3.6 PER encoding instructions (PER EIs): Notation used to change the unaligned PER encoding of a type (or of
a component of a type).
NOTE – PER encoding instructions are included in either a PER type prefix (see Rec. ITU-T X.680 | ISO/IEC 8824-1, 31.3) or a
PER encoding control section (see Rec. ITU-T X.680 | ISO/IEC 8824-1, clause 54).
3.7 PER EI proposal: A proposal for a new PER encoding instruction that is progressing to either the REJECTED
or the APPROVED state.
 Rec. ITU-T X.695 (08/2015) 1

---------------------- Page: 10 ----------------------
ISO/IEC 8825-6:2015 (E)
3.8 PER EI change proposal: A proposal for deletion of or change to an APPROVED PER encoding instruction
that is progressing to either the REJECTED or the APPROVED state.
NOTE – PER EI change proposals are expected to be rare occurrences, and due consideration will be needed to backwards
compatibility considerations.
3.9 prefixed encoding instructions: PER encoding instructions that are assigned using a type prefix (see Annex A
and Rec. ITU-T X.680 | ISO/IEC 8824-1, 31.3).
NOTE – Prefixed encoding instructions can delete, replace, or add to the associated encoding instructions of a type.
3.10 relevant Study Group: The ITU-T Study Group that is responsible for the Joint ITU-T | ISO/IEC JTC1
Collaborative Team for ASN.1.
3.11 relevant Sub-Committee: The ISO/IEC JTC1 Sub-Committee that is responsible for the Joint ITU-T | ISO/IEC
JTC1 Collaborative Team for ASN.1.
3.12 targeted encoding instructions: PER encoding instructions that are assigned using a target list in a PER
encoding control section (see Annex B and Rec. ITU-T X.680 | ISO/IEC 8824-1, clause 54).
NOTE – Targeted encoding instructions can delete, replace, or add to the associated encoding instructions of a type.
4 Abbreviations
For the purposes of this Recommendation | International Standard, the following abbreviations apply:
ASN.1 Abstract Syntax Notation One
ECN Encoding Control Notation
EI Encoding Instruction
PER Packed Encoding Rules
5 Notation
5.1 This Recommendation | International Standard references and uses the notation defined by Rec. ITU-T X.680 |
ISO/IEC 8824-1, clause 5 for the specification of the syntax of PER encoding instructions via a set of productions.
5.2 All lexical items used in these productions are defined in Rec. ITU-T X.680 | ISO/IEC 8824-1, clause 12.
5.3 In accordance with Rec. ITU-T X.680 | ISO/IEC 8824-1, 31.3.2, this Recommendation | International Standard
specifies the "EncodingInstruction" production (see 11.2).
NOTE – The "[" and "]" lexical items never appear in an "EncodingInstruction" production.
5.4 In accordance with Rec. ITU-T X.680 | ISO/IEC 8824-1, 54.4, this Recommendation | International Standard
specifies the "EncodingInstructionAssignmentList" production (see 12.1.2).
NOTE – The END and ENCODING-CONTROL lexical items never appear in the "EncodingInstructionAssignmentList" production.
6 Information to be provided to specify a PER encoding instruction
6.1 The specification of a PER encoding instruction shall consist of the following information:
a) a short informative title (such as "Use and size of a length field ");
b) the value for the identifying keyword, which shall be distinct from that used for any earlier PER EI;
c) an illustration of the syntax of the EI, enclosed in square brackets ("[" and "]");
d) a simple description of the EI and its purpose;
e) a full specification of the types to which this EI applies and its effect in each case;
f) a complete specification of an "EIDetail" production (see 11.4), with the semantics associated with each
element;
g) either:
1) an amendment to specific text in Rec. ITU-T X.691 | ISO/IEC 8825-2 that shall be applied to the
encoding of any type to which the EI is applicable (see d) above) and that has this EI in its set of final
encoding instructions; or
NOTE 1 – If the EI is not applicable to the type, then the amendment is not applied in the encoding of that
type.
2) an ECN specification of the effects of the encoding instruction; or
3) any other clear and implementable statement of the effects of the EI;
2 Rec. ITU-T X.695 (08/2015)

---------------------- Page: 11 ----------------------
ISO/IEC 8825-6:2015 (E)
4) any combination of 1) to 3).
NOTE 2 – Whilst option 3) is clearly desirable, it may be necessary to progress with options 1) or 4) and
add the others later so as not to delay approval of the EI.
NOTE 3 – The choice of options 1) to 4) has to be determined by whether the specification is sufficiently
clear and precise to enable interworking implementations of encoders and decoders to be produced.
h) a statement that the clauses or subclauses of Rec. ITU-T X.691 | ISO/IEC 8825-2 that are being amended
are disjoint from those amended by any previously approved encoding instruction that has an overlapping
list of types to which they can be applied.
7 Status of a PER EI proposal during the approval process
7.1 A PER EI proposal can be in one of the following categories:
– Considered but rejected (REJECTED): There has been some (documented) discussion, but this PER EI
proposal is unlikely to be progressed at this time.
– Suggested as possibly useful (POSSIBLE): The PER EI proposal is pending further discussion.
– Under active development (NEEDED): There is agreement that a PER EI performing this function is
needed, but the precise specification has still to be developed. Work is in progress to refine the specification
of this PER EI.
– Conditionally approved (READY): The full specification is available and ready for implementation. It
has been approved by either the relevant Study Group or by the relevant Sub-Committee by a Resolution
at a Plenary meeting.
– Approved (APPROVED): The full specification of the PER EI has been published in the READY state
for at least six months, and has been approved by both the relevant Study Group and the relevant Sub-
Committee by Resolutions at Plenary meetings.
NOTE – PER EI proposals in the NEEDED, READY, and APPROVED categories are published by the Registration
Authority (see clause 9). REJECTED and POSSIBLE PER EI proposals are recorded by the Joint ITU-T | ISO/IEC
JTC1 Collaborative Team for ASN.1 in standing documents.
7.2 A PER EI proposal will normally progress from an initial proposal into either the REJECTED or POSSIBLE
or NEEDED category, and then to the READY and later to the APPROVED category. However, at any stage prior to
moving to the APPROVED category, it can be moved to the REJECTED category.
NOTE – This will typically occur if problems are found with its implementation.
7.3 Once a PER EI proposal is in the APPROVED category (the PER EI is approved), it shall only be changed or
removed by a PER EI change proposal that shall move through all the above stages with the same approval processes
(specified in clause 8) before it results in the removal or modification of an APPROVED PER EI.
8 Approval process
8.1 Any member of the relevant Study Group and any member of the relevant Sub-Committee can generate a new
PER EI proposal by submitting at least the information in 6.1 a) to d) in the format of Annex A. Additional free-form text
with suggestions for e) to g) may also be included, and submitters of new EIs are encouraged to provide the full
information required for 6.1.
8.2 Discussion of the proposal shall take place at the next available main or interim meeting of either the relevant
Study Group or the relevant Sub-Committee. The proposal shall, after discussion, be placed in the category:
a) REJECTED: minutes of the meeting shall record the reasons for the rejection; or
b) POSSIBLE: details of the PER EI proposal shall be listed in a Standing Document of the Joint ITU-T |
ISO/IEC JTC1 Collaborative Team for ASN.1, recording proposed PER EIs, with the dates it was
proposed, considered and details of the proposer and any relevant discussion; or
c) NEEDED: details of the PER EI proposal shall be published (see clause 9).
8.3 A PER EI proposal shall progress to the NEEDED category from any interim or main meeting of the relevant
Study Group or the relevant Sub-Committee if and only if those present at the meeting agree unanimously and there is
text available for the public announcement, with the information required for 6.1 a) to f) approved by the meeting. Details
of the PER EI shall be published.
NOTE – This information is sufficient for syntax tools to be produced, and for users to include the PER EI in their draft
specifications.
 Rec. ITU-T X.695 (08/2015) 3

---------------------- Page: 12 ----------------------
ISO/IEC 8825-6:2015 (E)
8.4 A PER EI proposal shall progress to the READY category from any main meeting of the relevant Study Group
or the relevant Sub-Committee if and only if there is a formal Resolution at that meeting, based on availability and review
of complete text for all of 6.1 a) to h), that the PER EI proposal is approved by that relevant Sub-Committee or relevant
Study Group. The revised details of the EI shall be published.
8.5 A PER EI proposal shall progress to the APPROVED status if and only if the following conditions are satisfied:
a) the PER EI proposal has been in the READY category for at least six months;
b) both the relevant Study Group and the relevant Sub-Committee have passed a formal Resolution at a
Plenary meeting that they approve the PER EI.
9 Publication by the Registration Authority
9.1 All Registration and publication shall be via a Web page on a web-site of the relevant Study Group maintained
by the ITU Telecommunication Standardization Bureau that acts as the formal Registration Authority. The new contents
of this page shall be provided by the Joint ITU-T | ISO/IEC JTC1 Collaborative Team for ASN.1 when the status of a
PER EI proposal changes (see clause 8 for when such changes can occur).
NOTE 1 – The Web page at the time of publication can be located via the URL http://www.itu.int/ITU-T/studygroups/com17,
under the heading "Registration - Assignment", title "ASN.1 PER EIs".
NOTE 2 – Should these pages be moved, their new location can be obtained by an e-mail addressed to tsbmail@itu.int, asking to
be put in contact with the ITU-T Rapporteur responsible for the maintenance of Rec. ITU-T X.695 | ISO/IEC 8825-6.
9.2
...