The Encoding Control Notation (ECN) allows specifiers to define their own encoding rules by referencing standardized encoding rules and modifying some of their characteristics (for example, one may want to use the whole standardized PER set but for the boolean values that would remain encoded on octets), or even to set up completely new ones.
ECN will prove useful in application domains that require a particularly optimized transfer syntax (in terms of size or speed of encoding/decoding). All these standards describe data transfer as bit- or octet-fields in tables or (English) texts, sometimes without providing any ASN.1 modules. ASN.1's ability to model emerging protocols such as Bluetooth makes it ideal for working with protocols whose messages were originally defined without use of ASN.1.
A more systematic use of ASN.1 in the context of these protocols will make them more likely to be used in generic test-tools like those based on TTCN (Tree and Tabular Combined Notation) for example, and will prevent a plethora of informal encoding rules (unfit for validation), generally non-standardized, which may become the exclusive property of a single tool vendor.
ASN.1 can describe types, but for the time being there exists no formal notation that could define encoding rules. The encoding control will be modelled by a new category of modules called Encoding Definition Modules (EDM); they will contain the information (such as alignment, padding bits, computation of length field, etc) that defines the encoding to be associated with (some of) the generic ASN.1 standard types or specific types imported from another ASN.1 module.
In addition, a linkage module, called the Encoding Link Module (ELM), which is in principle very much similar to a makefile for Unix systems, will associate one or several modules with one or several encoding control modules (or with standardized encoding rules, like the PER aligned variant for example, together with an encoding control module in which some of these standardized rules are modified).
The encoding control standard is called ITU-T X.692 | ISO/IEC 8825-3
and has been approved in 2008.