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ASN.1 Project


Foundation of the Project

​The ITU-T Study Group 17 ASN.1 Project assist users of ASN.1 (Rec. ITU-T X.680, X.690 and X.890 series) within and outside of ITU-T, and promotes the usage of ASN.1 across a wide range of industries and standards bodies. 

It is the continuation of a part of the common ASN.1 and OID Project established in February 2001 by ITU-T Study Group 7 (now Study Group 17).

Scope of the project

  • Provide assistance to users of ASN.1 (Rec. ITU-T X.680, X.690 and X.890 series) within and outside the ITU-T.
  • Promote the usage of ASN.1 in new protocols.
  • Help the TSB in responding to requests they receive about ASN.1 usage.
  • Help the TSB in the maintenance of an up-to-date database of error-free ASN.1 modules. This database contains the modules of more than 200 ITU-T Recommendations and the modules of other SDOs referenced by them.

Management of the Project

​Paul Thorpe (United States) has been appointed as Project Leader. The Project Leader in consultation with the SG17 Chairman and TSB manages decisions related to the operation of the ITU-T Project including the use of its name and resources. All such decisions are reported to each Plenary session of SG17. 

The Project Leader establishes a close working relationship with the SG17 management team and with the Promotion, Edition and Production Department and other parts of the TSB.

Background on ASN.1

​ASN.1 is a well-established technology that is widely used both within ITU-T and outside of it. The notation is supported by a number of software vendors.

The initial set of encoding rules was Basic Encoding Rules, BER (Rec. ITU-T X.690) with canonical variants later defined in Distinguished Encoding Rules, DER and Canonical Encoding Rules, CER. All of these use a tag-length-value format of encoding.

In 1995, a more compact set of encoding rules, Packed Encoding Rules, PER ((Rec. ITU-T X.691) was defined for applications with bandwidth constraints, including four variants aligned and unaligned and basic and canonical.

The Encoding Control Notation, ECN (Rec. ITU-T  X.692), makes it possible for ASN.1 to be used for all existing telecom/computer protocols. This extends the use of ASN.1 into new areas, and increases the need for coordination of the activity.

The XML Encoding Rules, XER (Rec. ITU-T X.693), allows the encoding of ASN.1 values in XML markup format for the purpose of transmission. A canonical XML encoding is also specified in this document. ASN.1 can now be used as a schema for XML, in the same way as XSD and RELAX NG are used. 

The Octet Encoding Rules, OER (Rec. ITU-T X.696), allows the encoding of ASN.1 values in a format designed specifically for faster encoding and decoding.

The JavaScript Object Notation Encoding Rules, JER (Rec. ITU-T X.697), allows the encoding of ASN.1 values in Javascript Object Notation (JSON) format. This allows easier manipulation for human-readable display purposes.

The mapping from W3C XML Schemas into ASN.1 modules (Rec. ITU-T X.694) takes as input a schema written in XML Schema and produces an ASN.1 module containing a set of type definitions (and, optionally, an XER encoding instruction section to keep the same XML encoding, if needed), in such a way that there is a one-to-one correspondence between ASN.1 abstract values and valid XML instances. This technique can be applied to any given XML application language. ASN.1 standardized encoding rules such as DER (a canonical encoding that allows digital signatures and encryption, for example) or PER (to very efficiently transmit data over a radio channel, for example) can then be used as well as associated ASN.1 tools, or even specific encoding rules that are described in ECN.

Fast Infoset (Rec. ITU-T  X.891) specifies a representation of an instance of the W3C XML Information Set using ASN.1 binary encodings. This representation generally provides smaller encoding sizes and faster processing than a W3C XML representation. It provides the capability to encode XML content that is not described by a schema.

Fast Web Services (Rec. ITU-T X.892) is the term applied to the use of ASN.1 to provide message exchanges based on a SOAP envelope and WSDL specification of services that can have a higher transaction-processing rate and less bandwidth requirements than use of a character-based XML representation.

Rec. ITU-T X.893 "Generic Applications of ASN.1 - Fast Infoset and Fast Web Services Security" specifies the application of standard security methods to the Fast Infoset and Fast Web Services specifications.

ASN.1 module database

​The ASN.1 module database was initiated by France Telecom and donated to the ITU-T in November 2002.  The database currently contains over 964 ASN.1 modules corresponding to more than 200 ITU-T Recommendations. The maintenance of the database is handled by the Promotion, Edition and Production Department of the ITU TSB.

Implementations of the associated ITU-T Recommendations require an electronic format (using ASCII encoding) in order to directly process the formal definitions in current tools.  Obtaining an ASCII encoding from a printed or a post-script document involves re-typing, hinders speedy implementation and can introduce errors.  Having all ASN.1 modules (in ASCII format) in one place greatly eases implementation of the corresponding protocols. 

The TSB validation process is as follows: firstly, the module is extracted from the Recommendation; a syntax and semantics check is then performed and, if errors are found, a communication process is established with the Editor and Rapporteur of the Recommendation to solve these errors.  The modules are checked as soon as possible after Consent is given.  This allows errors to be corrected during the publication phase and ensures that the published Recommendations are error-free. 

Three validation tools were donated to the TSB: France Telecom donated Asnp, a syntax checker and HTML pretty-printer; OSS Nokalva donated their ASN.1 compiler; Opening Technologies donated their ASN.1/GDMO tool. 

An agreement was reached with ISO, IETF, ITU-R and UPU in order to include any of their ASN.1 modules referenced by ITU-T Recommendations.


​In cooperation with the Promotion, Edition and Production Department of the ITU TSB, the ASN.1 Project has established a database that contains a machine-processable copy of the current version of all ASN.1 modules that are included in ITU-T Recommendations (see previous section). 

TSB extended the module database with other formal descriptions used in ITU-T Recommendations, such as XML documentsGDMO definitions, and SNMP MIB modules.