stations can be improved considerably. 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. Shore-based AIS network systems are now being built up around the world. One of the biggest fully operational, real time systems with full routing capability is in China. This system was built between 2003 and 2007 and was delivered by Saab TranspondereTech. The entire Chinese coastline is covered with approximately 250 base stations in hot-standby configurations including 70 computer servers in three main regions. Hundreds of shore-based users, including about 25 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 SRMs (Safety Related Messages). All data are in real time. The system was designed to improve the safety and security of ships and port facilities. It is also designed according to an SOA architecture with socket based connection and using IEC AIS standardized protocol all the way to the VTS users. The base stations have hot-standby units (IEC 62320-1) and the network is the third generation network solution. By the beginning of 2007, a new worldwide standard for AIS base stations was approved, the IEC 62320-1 standard. The old IALA recommendation and the new IEC 62320-1 standard are in some functions incompatible, and therefore attached network solutions have to be upgraded. This will not affect users, but system builders need to upgrade software to accommodate the new standard. A standard for AIS base stations has been long-awaited. Currently ad-hoc networks exist with class A mobiles. Base stations can control the AIS message traffic in a region, which will hopefully reduce the number of packet collisions. Broadcast information An AIS transceiver sends the following data every 2 to 10 seconds depending on a vessel's speed while underway, and every 3 minutes while a vessel is at anchor: Vessel Maritime Mobile Service Identity (MMSI): a unique nine digit identification number. Navigation status: E.g., "at anchor", "under way using engine(s)", "not under command", etc. Rate of turn: right or left, from 0 to 720 degrees per minute Speed over ground: resolution from 0 to Positional resolution: Longitude: to arcminutes Latitude: to arcminutes Course over ground: relative to true north to 0.1° True heading: 0 to