N2K
NMEA 2000, abbreviated to NMEA2k or N2K and standardised as IEC 61162-3, is a plug-and-play communications standard used for connecting marine sensors and display units within ships and boats. Communication runs at 250 kilobits-per-second and allows any sensor to talk to any display unit or other device compatible with NMEA 2000 protocols. Electrically, NMEA 2000 is compatible with the Controller Area Network ("CAN Bus") used on road vehicles and fuel engines. The higher-level protocol format is based on SAE J1939, with specific messages for the marine environment. Raymarine SeaTalk 2, Raymarine SeaTalkNG, Simrad Simnet, and Furuno CAN are rebranded implementations of NMEA 2000, though may use physical connectors different from the standardised DeviceNet Micro-C M12 5-pin screw connector, all of which are electrically compatible and can be directly connected.
The protocol is used to create a network of electronic devices—chiefly marine instruments—on a boat. Various instruments that meet the NMEA 2000 standard are connected to one central cable, known as a backbone. The backbone powers each instrument and relays data among all of the instruments on the network. This allows one display unit to show many different types of information. It also allows the instruments to work together, since they share data. NMEA 2000 is meant to be "plug and play" to allow devices made by different manufacturers to communicate with each other.
Examples of marine electronic devices to include in a network are GPS receivers, auto pilots, wind instruments, depth sounders, navigation instruments, engine instruments, and nautical chart plotters. The interconnectivity among instruments in the network allows, for example, the GPS receiver to correct the course that the autopilot is steering.
The NMEA 2000 standard was defined by, and is controlled by, the US-based National Marine Electronics Association (NMEA). Although the NMEA divulges some information regarding the standard, it claims copyright over the standard and the contents thereof are thus not publicly available. For example, the NMEA publicizes which messages exist and which fields they contain, but they do not disclose how to interpret the values contained in those fields. However, enthusiasts are slowly making progress in discovering these PGN definitions.
...
Wikipedia