AIS Class A equipment has been a mandatory fit to the larger deep-sea vessels since 2004, following its specification just a few years earlier. Each unit contains a VHF modem and GPS receiver, and is capable of transmitting and receiving bursts of data including the vessel ID, position, course, speed, etc. Data received in this way can then be displayed by Harbour Authorities, Coastguards, and other vessels, on bespoke displays or overlaid onto charts or radar displays. It is an automated system so requires no manual intervention. And it is a truly global system, with the FCC having recently resolved a licensing dispute over North American use of AIS frequency 87-B.

The benefits for the vessel are two-fold. By transmitting your identity and position to local traffic on a regular basis, it makes sure they know you are there, and can take avoiding action if needed. And receiving this information from vessels in the vicinity means you know their course, speed, rate of turn etc and can take appropriate action yourself. And of course their identity and MMSI are displayed, so it is easy to make radio contact if needed. And then there are the enormous advantages for those concerned with vessel traffic services (VTS), anti-smuggling, anti-piracy and homeland security operations.

  Land-based AIS networks are rapidly covering the busiest coastal regions, but the network that currently eclipses them all is undoubtedly AISLive. A joint venture between Lloyd's Register/Fairplay of the UK and HITT Group of the Netherlands, it allows subscribers to view Global AIS data in near real time. In order to subscribe, companies and organisations are required to provide details of their activities within the maritime sector together with full contact information.  AISLive reserves the right to refuse access to the Industry service to any party. As well as real-time vessel information, the industry service offers ship search, arrival/departure notification (trigger) and alert facilities.

Of course, any AIS system depends on vessels being equipped with AIS equipment. Thankfully, the vast majority of deep sea vessels and passenger vessels should now be equipped with Class A systems. But as ever, it is impractical to burden smaller craft with the same expensive, powerful equipment as fitted to vast container ships and bulk carriers. A handful of lower-cost (and sometimes lower quality!) AIS Receivers have found their way to market - these will warn YOU that a vessel is in your vicinity, but will NOT warn THEM that you are there (losing the two-way advantage of the transponder).  AIS Class B was specified precisely to fill this gap - as a much less expensive, limited range and limited feature sub-set of the original. AIS Class B, as specified within IEC-62287-1, in fact operates slightly differently in the way transmissions are controlled (CSTDMA as opposed to SOTDMA), but it integrates seamlessly with the established existing Class A systems and equipment! The Class B CSTDMA specification was formally accepted in February 2006 as IEC 62287-1, after many months of simulation and verification (based on real  and forecast traffic densities in Florida and San Francisco) to confirm that it would not degrade the performance of the Class A networks unduly.

AIS Q and A...