This Amendment to ITU-T Rec. X.680 (1997) | ISO/IEC 8824-1:1998 introduces a notation that allows a version number to be specified when defining extensible types.  This makes it possible to clearly identify which version of an ASN.1 specification an extension addition applies to.


NOTE: All new or changed text in this document is highlighted in yellow in clauses/subclauses being replaced or modified.  When merging all such text into the base document the highlighting is to be removed.

Add at the bottom of clause 2.1 a reference to ITU-T Rec. X.692 | ISO/IEC 8825-3 as follows:

–           ITU-T Recommendation X.692 (2001) | ISO/IEC 8825-3:2001, Information technology – ASN.1 encoding rules: Specification of Encoding Control Notation (ECN).


Replace the definitions 3.8.26, 3.8.29, 3.8.74, add the new sub-clause 3.8.75, and renumber the currently existing 3.8.75 to 3.8.76 so that they read as follows below:

3.8.26   extension addition group: One or more components of a set, sequence or choice type grouped within version brackets. An extension addition group is used to clearly identify the components of a set, sequence or choice type that were added in a particular version of an ASN.1 module, and can identify that version with a simple integer.


3.8.29   extension insertion point (or insertion point): The location within a type definition where extension additions are inserted.  This location is the end of the type notation of the immediately preceding type in the extension series if there is a single ellipsis in the type definition, or immediately before the second ellipsis if there is an extension marker pair in the definition of the type.

NOTE – There can be at most one insertion point within the components of any choice, sequence, or set type.

3.8.74   version brackets: A pair of adjacent left and right brackets ([[ and ]]) used to delineate the start and end of an extension addition group. The pair of left brackets can optionally be followed by a number giving a version number for the extension addition group.


3.8.75   version number: A number which can be associated with a version bracket (see F.3).

NOTE – A version number cannot be added to an extension addition which is not part of an extension addition group, nor to extension additions to any type other than choice, sequence, or set.

3.8.76   white-space:  Any formatting action that yields a space on a printed page, such as the SPACE or TAB character, or multiple uses of such characters.



Add to clause 4 immediately after the abbreviation “DNIC” the following new abbreviation:

ECN            Encoding Control Notation

Add to clause 7 immediately before 7.1 the following note:

NOTE – These requirements apply to standardized encoding rules.  They do not apply to encoding rules defined using Encoding Control Notation (ECN).



Change the note in 7.3 so that it reads as follows:

NOTE 1 – All variants of the Basic Encoding Rules of ASN.1 and the Packed Encoding Rules of ASN.1 satisfy all these requirements.  Encoding rules defined using ECN do not necessarily satisfy all these requirements, but may do so.

NOTE 2 – PER and BER do not identify the version number in the encoding of an extension addition. Encodings specified using ECN may or may not provide such identification.


Change the “ExtensionAdditionGroup” production in 24.1, and add a production for “VersionNumber” so that they read as follows: