This Standard defines rules for the digital representation of data, for the transfer of tactical data via local area networks within a platform.

It is applicable to the specification of data elements and parameters passing to or from Combat System sub-systems, and in particular to the formulation of data at the Presentation Layer (layer 6) of the International Standards Organisation (ISO) seven layer model for Open System Interconnection (OSI).

The rules defined in this standard set out how the values of data parameters may be encapsulated in the data elements of messages to be transmitted by digital means. The various types of data parameter are set out in Section 6 of this standard. A data parameter, within the context of this standard, is the value range that may be assigned to a system variable that is to form part or all of the data content of a message. A number of different parameter types are defined that require one or more bits to convey the desired information. The method of transmission is defined on the basis of data organised as groups of 8-bit bytes, and as a consequence the data elements of a message will consist of one or more bytes which may include unused bits and / or more than one data parameter. The rules establishing the constraints on the format of the various data element formats are set out in Section 7.

The rules for data parameter representation defined in this standard implement a universal, byteoriented method of coding digital information that permits the transfer of information between processing devices that may have different architectures. The rules specify the development of the format for transmission of individual parameters.

The rules do not indicate the arrangement of any sequence of parameters, i.e. organisation of messages. The description of the parameter formats developed using this standard, and the organised arrangement of a sequence of parameters into a data message, is covered in an associated Message Construction Standard [6].

This standard was derived from the T45 DRS [15] which was originally derived from the Horizon Data Representation Standard [12], which in turn was based upon the NATO Standard for the Digital Representation of Shipboard Parameters, STANAG 4222 [4]. Not all the options included within STANAG 4222 [4] have been adopted within this standard; for example, reference key and alphanumeric identifiers have been omitted for reasons of efficiency. If additional items from the STANAG [4] are adopted then this standard will require update.

Where any conflict or doubt as to interpretation may occur between this document and STANAG 4222 [4], this standard shall be taken as the authoritative document. The applicability of this document will be determined by the Platform Data Manager.

It should be further noted that in architectures using a variety of networks, message designers need to take account of the syntax differences between the data representations in Def-Stan 21-26 Part 1 [14] and this standard.

Purpose

The purpose of this standard is to define rules for the digital representation of data, for exchange of data on any RN platform.