USER MANUAL
MTU AIS-C
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1.6.
THE SOTDMA PROTOCOL.
The AIS system employs for communications a self-organized time-division protocol that has
been inherited from air navigation.
This protocol allows a transponder to quickly integrate into a data network via radio along with
other equipment without interference or data collisions.
The protocol also allows communications between terminals in the same way as it is done on
GSM telephony networks.
The protocol has a 60s window with 2250 slots and includes 256 bits in each slot.
Each AIS unit has 2 receivers and a transmitter that can transmit in both AIS1 and AIS2 bands as
shown in the figure.
This transmission format allows data refresh up to a maximum speed of 2 seconds, spreading
half the stream load on each channel. This allows simultaneous ship-ship and ship-to-land
communications.
The coverage and distance of communications will depend on the transmission powers (usually
12W on ships and between 2 and 12 W in AtoN); and antennas and their location above MSL sea
level.
