The intent of this document is to provide general and specific design guidance for the development and installation of the protocols needed to exchange bit-oriented data using an air-ground HF data link operating in an Open System Interconnection (OSI) environment. The protocols defined herein are consistent with the concepts of the Aeronautical Telecommunications Network (ATN).

This document describes the functions to be performed by the airborne components of the HF Data Link System (HFDL) to successfully transfer messages between HF ground stations and avionics systems on aircraft where the data is encoded in a bit-oriented format. These functions are referred to as HFDL protocols. The compatibility with OSI is provided by defining a set of services and protocols in accordance with the OSI model.