Frequencies of AIS

1. Class A: Mandated for all vessels 300 GT and above engaged on international voyages as well as all passenger ships
2. Class B: Provides limited functionality and is intended for non-SOLAS vessels. Primarily used for vessels such as pleasure crafts

AIS operates principally on two dedicated frequencies or VHF channels:

• AIS 1: Works on 161.975 MHz- Channel 87B (Simplex, for the ship to ship)
• AIS 2: 162.025 MHz- Channel 88B (Duplex for the ship to shore)

It uses Self Organizing Time Division Multiple Access (STDMA) technology to meet the high broadcast rate. This frequency has a limitation on the line of sight which is about 40 miles or so.