The AIS transponder uses 9.6 kbps Gaussian Minimum Shift Keying (GMSK) FM modulation over 25 or 12.5 kHz channels defined by ITU-R Rec. 1084-2 and Appendix S18 of RR, using HDLC (High-Level Data Link Control) packed protocols. Each station transmits and receives over two radio channels to avoid interference problems, and to be shifted without communications loss from other ships. These channels are allocated to the international channel and regional frequency.
– AIS1: 161.975 MHz (CH87B; 2087)
– AIS2: 162.025 MHz (CH88B; 2088)
– Regional frequency (156.025 MHz to 162.025 MHz)
The operation of regional frequency is assigned from 20 to 200 NM rectangle area. The operation on these channels is accomplished by the following means:
– VHF DSC (CH70) commands from shore-based AIS;
– TDMA (AIS message) commands from shore-based AIS;
** Refer to Message 22: Channel management **
– Commands from shipboard system such as ECDIS, etc. (ACA); and
