Purpose of this Document

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 across an air-ground VHF Digital Link (VDL) in an Open System Interconnection (OSI) environment. Details of the VDL Mode 2 protocols defined herein are specified in the International Civil Aviation Organization (ICAO) VDL Mode 2 (VDLM2) Standards and Recommended Practices (SARPs) and in the ICAO Doc 9776 Manual on VHF Digital Link (VDL) Mode 2 Part II. VDLM2 is consistent with the concepts of the ICAO Aeronautical Telecommunication Network (ATN).

This document describes the functions to be performed by airborne and ground components of the VDLM2 to successfully transfer messages from VHF ground networks to avionics systems on aircraft, and vice versa, where the data are encoded in a code and byte independent format. The compatibility of VDLM2 with OSI is established by defining a set of services and protocols that are in accordance with the OSI basic reference model. The compatibility with the ATN protocols is achieved by defining a set of interfaces between the VDLM2 subnetwork protocol specification and the Mobile Subnetwork Dependent Convergence Function: (MSNDCF). The Subnetwork Dependent Convergence Function (SNDCF) is defined in the ICAO ATN SARPs.

COMMENTARY

VDLM2, as used in this document refers to the digital communication protocols to be exercised by the VHF transceiver and supporting avionics to exchange messages with any appropriately equipped ground system. The VDLM2 definitions were introduced to enhance the effectiveness of Air Traffic Services (ATS) and Aeronautical Operational Control (AOC) communications.