Maritime navigation and radiocommunication equipment and systems – Digital interfaces – Part 3: Serial data instrument network (Edition 1.1; Consolidated Reprint)
This part of IEC 61162 is based upon the NMEA 2000 standard. The NMEA 2000 standard contains the requirements for the minimum implementation of a serial-data communications network to interconnect marine electronic equipment onboard vessels. Equipment designed to this standard will have the ability to share data@ including commands and status@ with other compatible equipment over a single signalling channel. Data messages are transmitted as a series of data frames@ each with robust error check confirmed frame delivery and guaranteed latency times. As the actual data content of a data frame is at best 50 % of the transmitted bits@ this standard is primarily intended to support relatively brief data messages@ which may be periodic@ transmitted as needed@ or on-demand by use of query commands. Typical data includes discrete parameters such as position latitude and longitude@ GPS status values@ steering commands to autopilots@ finite parameter lists such as waypoints@ and moderately sized blocks of data such as electronic chart database updates. This standard is not necessarily intended to support high-bandwidth applications such as radar@ electronic chart or other video data@ or other intensive database or file transfer applications. This standard defines all of the pertinent layers of the International Standards Organisation Open Systems Interconnect (ISO/OSI) model@ from the application layer to the physical layer@ necessary to implement the required IEC 61162-3 network functionality. This standard defines data formats@ network protocol@ and the minimum physical layer necessary for devices to interface. SOLAS applications shall employ redundant designs (for instance dual networks@ redundant network interface circuits) to reduce the impact of single point failures. The NMEA 2000 standard provides the fundamental tools and methods to support redundant equipment@ buses and messaging. Specific shipboard installation designs are beyond the scope of this standard@ however some guidance is given in Annex A.