Marine Systems
Aviation Recorders
Rev. 02 Page 1--11
July 29/03
Automatic Identification System
1.3.7. DSC Functionality
The Assigned and Polled operational modes are activated through a DSC message
transmitted by the competent authority. In order to provide for this, the ProTec AIS
contains a dedicated DSC receiver that is tuned to channel 70. DSC messages
originating from shore stations of competent authorities will define regional AIS fre-
quencies, regions of coverage, required transmission schedule and/or interrogation
request. The ProTec AIS will respond back to such DSC interrogations on the fre-
quency specified in a manner such that it does not interfere with the TDMA transmis-
sions by interleaving the transmission between TDMA transmissions. The DSC re-
sponse will be made after a random delay of 0 -- 20 secs provided the signaling
channel is clear and the TDMA transmissions are not interrupted.
1.3.8. AIS Broadcast Parameters
A Class A AIS unit broadcasts the following information every 2 to 10 seconds while
underway, and every 3 minutes while at anchor at a power level of 12.5 watts. The
information broadcast includes:
F MMSI number -- unique referenceable identification.
F Navigation status
F Speed over ground -- 1/10 knot resolution.
F Position accuracy -- differential GPS.
F Longitude -- to 1/10000 minute and Latitude -- to 1/10000 minute.
F Course over ground -- relative to true north to 1/10th degree.
F True Heading -- 0 to 359 degrees derived from heading sensor.
F Time stamp -- The universal time to nearest second that this information
was generated.
In addition, the Class A AIS unit broadcasts the following information every 6
minutes:
F MMSI number -- same unique identification used above, links the data
above to described vessel.
F IMO number -- unique referenceable identification (related to ship’s
construction).
F Radio call sign -- international call sign assigned to vessel, often used on
voice radio.
F Name -- Name of ship, 20 characters are provided.
F Type of ship/cargo -- there is a table of possibilities that are available.
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