Encoding Control Notation (ECN)


Encoding Control Notation (ECN) is an internationally standardized formal notation used to specify specialized encoding rules for ASN.1. It is developed and maintained by ITU-T as ITU Recommendation X.692 (ISO/IEC 8825-3).

While ASN.1 specifications only deal with data that has semantics for the communicating applications, ECN specification defines the way auxiliary fields that are specific to the encoding are inserted.

In specifying the encoding rules with ECN, two approaches can be taken:

  • design of a complete set of (new) encoding rules or
  • overloading/specialization of standardized rules (such as PER).

For most protocol specifications, ASN.1 abstract specifications with standardized encoding rules yield sufficiently compact transfer syntax. In situations where this is felt insufficient, ECN can be deployed.

Both ASN.1 and ECN specifications can be checked by tools and coders/decoders can automatically be generated.


ETSI MTS members had opted for quick publication of the ITU-T draft X.692 recommendation with the intention to withdraw it as soon as the ITU-T final version was available. The following TS was withdrawn in 2003:

TS 101 969 - Methods for Testing and Specification (MTS); Abstract Syntax Notation One (ASN.1) encoding rules; Specification of Encoding Control Notation (ECN) [Draft ITU-T Recommendation X.692]

If there is future work:

A full list of standards related to ECN is accessible via the ETSI standards search. Via this interface you can also subscribe for alerts on updates of ETSI standards.

For work in progress see the ETSI Work Programme on the Portal.