This heading is further divided into procedure, preamble, address, and prefix.
The 16-line format and procedures for transmitting it vary slightly depending on the communications medium, but all variations are designed to be harmonious and the procedures describe how to convert (refile) between the formats.
The concept of the standard message format originated in the wired telegraph services.
Each telegraph company likely had its own format, but soon after radio telegraph services began, some elements of the message exchange format were codified in international conventions (such as Articles 9, 22, 26, 29, 30, and Appendix 1 of the International Radiotelegraph Convention, Washington, 1927), and these were then often duplicated in domestic radio communications regulations (such as the FCC in the U.S.) and in military procedure documentation.
For example, the publication "Communication Instructions, 1929",[6] from the U.S. Navy Department, includes: Technical Manuals Field Manuals Tables of Organization and Equipment (TOE) Army Regulations Forms Training Material And their modern decedents in the Allied Communications Procedures Training for message handling may (or may not) be found listed in the following documents: