At the start of the next period a new slot is randomly selected.
Type testing and approval[ edit ] AIS is a technology which has been developed under the auspices of the IMO by its technical committees. An AtoN will broadcast its position and Identity along with all the other information.
In the first transmission it announces its intention to use this slot for the following 8 minute period. All stations share a common time reference derived from GPS time ensuring they can all accurately determine the start time of each TDMA slot.
Hundreds of shore based users, including about twenty-five vessel traffic service VTS centers, are connected to the network and are able to see the maritime picture, and can also communicate with each ship using SRM's Safety Related Messages. The specification for each product type provides a detailed technical specification which ensures the overall integrity of the global AIS system within which all the product types must operate.
CSTDMA transceivers listen to the slot map immediately prior to transmitting and seek a slot where the 'noise' in the slot is the same or similar to background noise, thereby indicating that the slot is not being used by another AIS device.
Aids to navigation The AIS aids to navigation AtoN product standard was developed with the ability to broadcast the positions and names ultimate blackjack tour objects other than vessels, such as navigational aid hero altar slot marker positions and dynamic data reflecting the marker's environment e.
Maritime security AIS enables authorities to identify specific vessels and their activity within or near a nation's Exclusive Economic Zone. The system is backward compatible with digital selective calling systems, allowing shore-based GMDSS systems to inexpensively establish AIS operating channels and identify and track AIS-equipped vessels, and is intended to fully replace existing DSC-based transceiver systems.
Class A's must have an integrated display, transmit at The technical committees have developed and published a series of AIS product specifications. It transmits data as follows: In practice, the capacity of the system is nearly unlimited, allowing for a great number of ships to be accommodated at the same time.
Low-cost Class B transceivers became available in the same year triggering mandate adoptions by numerous countries and making large-scale installation of AIS devices on vessels of all sizes commercially viable.
The system provides for automatic contention resolution between itself and other stations, and communications integrity is maintained even in overload situations. Federal Communications Commissionand Industry Canadaall of which require independent verification by a qualified and independent testing agency.
The received information can be displayed on a screen or chart plotter, showing the other vessels' positions in much the same manner as a radar display. Default transmit rate is normally every 30 seconds, but this can be varied according to vessel speed or instructions from base stations.
If the signal strength at the start of the slot is close to the background level the slot is assumed to be unused and the transmission is made.
Slot selection by an AIS station is randomized within a defined interval and tagged with a random timeout of between 4 and 8 minutes.
Slot time - Wikipedia