Many AIS messages target specific MMSI. This means a Vessel or VTS (Vessel traffic service), or AtoN (Aid to Navigation) targets its messages to a certain MMSI destination. These messages can be binary, ASCII, Acknowledgements, GPS corrections, interrogations or assignment mode commands.
Here is a list of possible AIS messages.
Looking at the more complete picture of AIS directed communications coming over AISHUB, we get the following graphs, consisting out of messages 6,7,10,12,13,15,16.
These stations could be identified as major communication hubs.
MO OS WINDFARM
999028 Yantai VTS
560002 SINGAPORE VTIS
Japan and China dominate most of the AIS directed traffic.
Data was analysed over several weeks using an extended self written fork of aisparser and logged in MySQL from AISHUB and analysed in Gephi. The total number of analysed messages was more than a million.