Reception of AIS data
with multiplex receivers
The class A AIS service is described in the ITU-R M.1371-1 document. The -R stands for recommendation. This standard is a general document for the AIS service containing recommendations for the class A and B services. The document dated in 2001.
Operation of class A transponders is described in the EN61993-2. This document is obligatory for class A and was published in 2002.
Operation of class B transponders is described in the EN62287. This document is obligatory for class B and was published in 2005.
Class A: EN61993-2-2002:
The class A operation consists of three different types of messages:
- Dynamic information:
- MMSI number
- position of the ship (derived from GPS)
- time, when the position was measured in UTC
- course over ground (COG)
- speed over ground (SOG)
- heading (HOG)
- ship status
- rotational speed/turn rate
- Static information:
- call sign and name of the vessel
- ength and width of the vessel
- IMO-number of the vessel, if existent
- type of vehicel
- position of the GPS sensor onboard
- Journey-related information:
- draught of the vessel
- type of cargo
- port of destination and estimated time of arrival (ETA)
- route plan, optional
The block of dynamic information is the most important block looking for threatening collisions. Therefore this block of information is transmitted in a compulsory way, depending on the vessels movement.
The following table shows the mandatory repetition rate of class A transmissions linked to the ships movement:
- Anchored vessels: 3 minutes
- Vessels at 0 – 14 kn: 10 seconds
- Vessels at 14 – 23 kn: 6 seconds
- Vessels at > 23 kn: 2 seconds
- Vessels at 0 – 14 kn, fast manoeuvre: 3.3 seconds
- Vessels at 14 – 23 kn, fast manoeuvre: 2 seconds
- Vessels at > 23 kn, fast manoeuvre: 2 seconds
Static information as well as information belonging to the journey is dispersed every 6 minutes. The reporting intervals correspond to both radio channels (161.975 MHz, 162.025 MHz) together.
Class B: EN62287, 2005: class B operation is described in the standard EN62287, published in 2005. This document is obligatory for class B. Pages 15 and 38 describe the operation:
Reporting intervals are:
Dynamic ship data:
- Boats at < 2kn: 3 minutes
- Boats at > 2kn: 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 automatism to change the 30sec/3min dynamic intervals by the ship itself.