This part of IEC 61334 defines a set of encoding rules - the A-XDR encoding rules - that may be used to derive the specification of a transfer syntax for values of types defined in the DLMS core standard using the ASN.1 notation (see IEC 61334-4-41). These A-XDR encoding rules are also to be applied for decoding such a transfer syntax in order to identify the data values being transferred.
The A-XDR encoding rules
· are used at the time of communication;
· provide optimal encoding for DLMS PDUs.
NOTE Provided that A-XDR ensures optimal encoding for DLMS PDUs, it is intended to be the default encoding rule for DLMS-based communication protocols. Nevertheless, the default - and also the possibly usable optional - encoding rules will be specified in the Application Layer document of the given protocol (for example, IEC 61334-4-42), as part of the Application context.
note: 3) A-XDR stands for Adapted XDR. In fact, these encoding rules are derived from a proven and de facto standard of the Unix world, called XDR (external Data Representation, rfc1014).
4) See footnote 2 of the introduction.