Archivos diarios: julio 8, 2015
This summer two announcements by the National Marine Electronics Association (NMEA) highlighted the ways that the marine electronics field is like many of the boaters it serves: it has a fondness for the latest technology yet with a deep conservatism in not wanting to change what works.
One of the announcements detailed the advent of NMEA support for sending NMEA 2000 (N2K) network data via Ethernet. Called OneNet, the approach would allow N2K traffic to be compatible with Ethernet, allowing the two systems to work together. Ethernet is not new, of course, the networking protocol has been around for some time and is the standard method for computers, printers, scanners, game consoles, etc., to share data over a wired network. What Ethernet on a boat represents, however, is the very current trend to use large data rates for data hungry applications such as radar, electronic chart displays, video camera feeds and night vision/infrared video. These devices/applications all require moving large amounts of data at rates that are way beyond the capabilities of the N2K networking setup. So the NMEA moving to support N2K and Ethernet interconnectedness makes sense.
One thing that the OneNet setup will not do is to vanquish N2K. That networking protocol is designed around the CANBus architecture and has the mission to prioritize messages in a way that the most important messages are routed through and not “stepped on” by other devices. An example might be the helmsman on a vessel in a turn needs to know rudder angle data more than he needs to know water temperature or which song is playing on the boat’s sound system. “NMEA OneNet does not replace NMEA 2000,” said Steve Spitzer, NMEA technical director, in the recent NMEA OneNet announcement. “NMEA OneNet uses the physical and network layer standard based on the IEEE 802.3 Ethernet standard…. OneNet is not recommended for real-time critical data, because the NMEA 2000 controller area network (CAN) enables prioritization and guarantees that the message will always get through to certified devices. IEEE 802.3 cannot provide the same guarantee of message delivery.”
According to NMEA, the primary goals of OneNet are to transport N2K network messages on Ethernet; interoperate with the established N2K networks; establish standardized gateway rules between N2K and OneNet and support high bandwidth applications such as video, which is not possible using the N2K network.
Some key features of OneNet include:
Greater bandwidth: Up to 1 gigabit or faster transfer speed directly to OneNet devices.
Scalability: OneNet backbones may exceed 100 Mbits/sec.
More devices supported: OneNet can support up to 65,024 physical devices versus CANbus’s 50 devices.
Greater power capacity: With power over Ethernet, each physical device may be separately powered by up to 15.4 watts.
Video: OneNet incorporates existing video standards.
Ethernet everywhere: Ethernet is used in a wide variety of environments and is well understood.
The OneNet standard is still a work in progress and is scheduled to be completed and ready for prime time in 2014. Some critics of NMEA have long pushed for the adoption of Ethernet as a marine networking standard and will no doubt be unhappy that NMEA-sanctioned N2K/Ethernet integration is still two years away. But OneNet should provide a reliable, standardized method to interoperate N2K and Ethernet and bring additional capabilities to marine electronics.
While the OneNet announcement looks to the future, the other recent NMEA announcement involves an established technology that continues to play a useful role on board: the big brother to N2K, the venerable NMEA 0183 standard.
According to NMEA, the definition of NMEA 0183 is that it “defines electrical requirements, data transmission protocol and timing, and specific sentence formats for a 4,800-baud serial data bus.” This newest version of 0183 is version 4.10, which replaces version 4.0 which came out in 2008, and is backwards compatible to version 2.0 from 1992. The original version of 0183 goes back to the 1980s.
The latest updates to the 0183 standard include expansions of various electronic communications “sentences” that relate to the highly popular and rapidly growing area of automatic identification systems (AIS) and to the upcoming European satellite system called Galileo, which will be similar to and interoperable with GPS.
AIS continues to be tweaked by the International Telecommunications Union and so the NMEA 0183 standard has adjusted with some enhancements to a number of AIS sentences and the development of new ones.
So far, Galileo is a satellite navigation system very much still in development. The European community has pledged to launch the satellites, which are in middle Earth orbit just like GPS spacecraft, and to complete the buildout of the system. Two Galileo test satellites were launched in 2005 and 2008. These were followed by two operational satellites in October 2011. Two more satellites were reportedly to be launched this year. According to the European Space Agency, however, the full Galileo constellation of 30 satellites (27 operational and three in-orbit spares) is not scheduled to be operational until 2019.