The Automatic Identification System or AIS as it's normally understood is a VHF based ship recognition system that has been in use since 1999. It's a compulsory requisite for most ships of three hundred gross tons that are engaged in international voyages.
The AIS system has proved to be a blessing for collisions amongst ships and is also widely used in assisting Vessel Traffic Services (VTS). A fairly recent development in that technology has been the advent of the Virtual Automatic Identification System. You can find the best AIS system via the web.
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The Virtual Automatic Identification System is based on the concept of Pseudo Automatic Identification System messaging. PAIS is basically an AIS content broadcast by Vessel Traffic Services centers to supply ships. This information pertains to towing vessels and relaying messages to other ships that don't have Automatic Identification System equipment.
The VTS center sends a pseudo-AIS message on behalf of the towing vessel to ships in the vicinity so that they can give the towing vessel a wide berth. The idea of pseudo-AIS has been driven one step ahead with the introduction of Virtual Buoys and Virtual Pilots.
A Virtual Buoy is basically an AIS message sent by the Vessel Traffic Services to ships in the port arena. It conveys the information in regards to navigational buoys that are not physically present. This kind of system is highly cost-efficient as the expenses involved in setting up and keeping up a physical buoy are negated.