A functioning AIS transponder keeps transmitting information even when the subject vessel is anchored. The information contained in each AIS-data packet (or message) can be divided into the following two main categories:
Dynamic Information
(such information is automatically transmitted every 2 to 10 seconds depending on the vessel's speed and course while underway and every 6 minutes while anchored from vessels equipped with Class A transponders)
Maritime Mobile Service Identity number (MMSI) - a unique identification number for each vessel station (the vessel's flag can also be deducted from it)
AIS Navigational Status (read more on the subject)
Rate of Turn - right or left (0 to 720 degrees per minute)
Speed over Ground - 0 to 102 knots (0.1-knot resolution)
Position Coordinates (latitude/longitude - up to 0.0001 minutes accuracy)
Course over Ground - up to 0.1° relative to true north
Heading - 0 to 359 degrees
Bearing at own position - 0 to 359 degrees
UTC seconds - the seconds field of the UTC time when the subject data-packet was generated.
Static & Voyage related Information
(such information is provided by the subject vessel's crew and is transmitted every 6 minutes regardless of the vessel's movement status)
International Maritime Organisation number (IMO) - note that this number remains the same upon transfer of the subject vessel's registration to another country (flag)
Call Sign - international radio call sign assigned to the vessel by her country of registry
Name - up to 20 characters
Type (or cargo type) - the AIS ID of the subject vessel's shiptype
Dimensions - approximated to the nearest metre (based on the position of the AIS Station on the vessel)
Location of the positioning system's antenna on board the vessel
Type of positioning system (GPS, DGPS, Loran-C)
Draught - 0.1 to 25.5 metres
Destination - up to 20 characters
ETA (estimated time of arrival) - UTC month/date hours:minutes
It is important to notice that the vessel's crew or the accountable vessel's officer should make sure that they provide the system with the correct information regarding all static and voyage-related fields.
Note also that Class B transponders transmit a reduced set of data compared to Class A (IMO number, Draught, Destination, ETA, Rate of Turn, Navigational Status are not included). The reporting intervals from Class B transponders are also scarcer compared to those of Class A transponders (30 seconds minimum).