Classes of AIS

ITU-R Recommendation M.1371-1 describes the following types of AIS:

Class A

Shipborne mobile equipment intended for vessels meeting the requirements of IMO AIS carriage requirement.

Class B

Shipborne mobile equipment provides facilities not necessarily in full accord with IMO AIS carriage requirements. IEC has begun work on a Class B certification standard, which should be completed by 2003/2004. The Class B is nearly identical to the Class A, except the Class B:

Has a reporting rate less than a Class A (e.g. every 30 sec. when under 14 knots, as opposed to every 10 sec. for Class A)
Does not transmit the vessel’s IMO number or call sign
Does not transmit ETA or destination
Does not transmit navigational status
Is only required to receive, not transmit, text safety messages
Is only required to receive, not transmit, application identifiers (binary messages)
Does not transmit rate of turn information
Does not transmit maximum present static draught

Search and Rescue Aircraft

Aircraft mobile equipment, normally reporting every ten seconds.

Aids to Navigation

Shore-based station providing location of an aid to navigation. Normally reports every three minutes. This may eventually replace the racon.

AIS base station

Shore-based station providing text messages, time synchronization, meteorological or hydrological information, navigation information, or position of other vessels. Normally reports every ten seconds.

AIS Frequencies

The International Telecommunications Union World Radio Conference in 1997 designated two VHF radio frequencies: 161.975 MHz (AIS1, or channel 87B) and 162.025 MHz (AIS2, or channel 88B) for AIS. In the US, the first channel is owned by MariTEL, a public coast station operator, and the second by the federal government. The USCG signed a Memorandum of Agreement with MariTEL for use of AIS 1, and has authority from the National Telecommunications and Information Administration to use both AIS1 and AIS 2 US-wide for AIS operation. The USCG has asked the Federal Communications Commission to authorize any US vessel to operate AIS on these two channels under its existing ship station license. The FCC released a Notice authorizing operation of AIS under a ship's existing station license.

Most of the information on this page has been taken from USCG (www.navcen.uscg.goc/marcomms/ais.htm) and is from 2002.

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