 The material aims to facilitate the understanding of detailed technical provisions that are contained in the Manual of Technical Provisions for the Aeronautical Telecommunication Network (ATN) (Doc 9705), and thus to assist in the planning and implementation of the ATN.AOC were often user-defined, because they were only exchanged between an airline and its own aircraft; controlling both ends, there was no need for standardization.However, by introducing airframe-defined ACARS messages (e.g.