[https://store.icao.int/comprehensive-aeronautical-telecommunication-network-atn-doc-9739-english-printed.html COMPREHENSIVE AERONAUTICAL TELECOM NETWORK (ATN) MANUAL 1ST EDITION - 2000 (DOC 9739) - ENGLISH - PRINTED https://store.icao.int/comprehensive-aeronautical-telecommunication-network-atn-doc-9739-english-printed.html