Transmission types

There are different types of AIS transmissions, each serve different AIS products and behave in different ways.

Self Organised Time Division Multiple Access (SOTDMA) is designed for Class A units who reserve their space in the AIS slot map.

Carrier Sense Time Division Multiple Access (CSTDMA) is designed for Class B units who scan for available space in the AIS slot map.

Fixed Access Time Division Multiple Access (FATDMA) is mainly used by AIS Base stations and AIS Aids to Navigation.

Random Access Time Division Multiple Access (RATDMA) is mainly used by Aids to Navigation who don’t have their transmission space controlled by base stations and have to scan for available space in the AIS slot map. It is also used by Class units in some situations.

Pre Announced Time Division Multiple Access (PATDMA) is designed for SARTs.

Incremental Time Division Multiple Access (ITDMA) is used by AIS devices to pre announce their AIS data transmissions.