VHF Data Link
The VHF Data Link or VHF Digital Link (VDL) is a means of sending information between aircraft and ground stations (and in the case of VDL Mode 4, other aircraft) over VHF. Aeronautical VHF data links use the band 117.975–137 MHz which was assigned by the International 'T'elecommunication 'U'nion (ITU) in the ITU Radio Regulations Article 1 to the Aeronautical Mobile (R) Service or short AM(R)S. International Standards and Recommended Practices (SARPs) and guidance material for VHF Digital Link (VDL) Mode 1 and Mode 2 were published first by the International Civil Aviation Organization (ICAO) in ICAO Annex 10, Volume III and Volume V in 1997 as a part of Amendment 72. In 2001 additional material was published in ICAO document Doc-9976, the Manual on VHF Digital Link (VDL) Mode 2.