Quick Instruction, Version 2.2
Page 13 of 43 pages
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boats at > 2 kn: 30 seconds
static ship data (similar to class A): 6 minutes
These intervals are the standard operation modes.
Competent authorities, like base stations, can have influence on the
reporting intervals (as they do with class A as well). Interval timing can
be reduced down to 5 seconds in exceptional cases. There is no automat-
ism to change the 30sec/3min dynamic intervals by the ship itself.
Think about
The comparison is done only for dynamic data transmission, because
these datasets contain the relevant information to calculate a future
collision point in time and distance, as well as allow the threatened ships
to communicate (MMSI number is stringent part of dynamic data infor-
mation) by VHF. Additionally, 2 more facts concerning class B operation
need to be mentioned:
Unlike the class A service, which is using the SOTDMA method (self or-
ganized time division multiple access) with predefined timeslots (the
ship listens to the traffic and the information containing in all other
telegrams and defines its own raster of transmission timing, which is
then distributed to all other participants within the radio range) the
class B service is using a “listen-before-talk-method”. This means, that
before transmitting, a ship has to observe the radio channel, whether to
be allowed to transmit, if the channel is not occupied, or whether to
wait for a free time slot.
To avoid disturbance of the professional class A service in crowded
areas, higher-ranking authorities can switch off all class B transponder
activities, which will probably never happen, but it should be men-
tioned
.
Above given information is not complete and should give only an over-
view about the AIS topic. For more details please have a look to the
following links:
