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AIS Integration


The subject of AIS integration has cropped up repeatedly so I thought I'd shed some light on the subject.
We deal with Ethernet networks, so while the YachtSurfer products do not have a connector for NMEA-0183 or NMEA2K, that doesn't mean you cant integrate your chart plotter or sensors into your Navigation Apps for iPads or PCs.
The great thing about ethernet is that it is a universal transport standard. Anything with an Ethernet connector will connect to the network. It matters little what the actual data carried within the Ethernet packet contains. By using Ports & Tags, data is segregated and can be delivered to the device requiring it or requesting it.
Lets look at web browsing; web servers use port 80 by default, so when a user clicks on a link in their browser, this request is tagged with the browser instance, device IP address and is set to the host via the network routers the web server is listening on Port 80 for new requests and responds, sending the data back. The network routers direct this data to the requesting device using the IP Address and the browser displays the data on the correct browser window. This is the TCP protocol (Transmission Control Protocol) and it connects 2 computers directly with each other for the transmission of data - port 80 (or any TCP Port) can be used by multiple computers on the same network concurrently without issue. TCP is comparable to a phone converstation, a number is dialed, connected, a conversation takes place and both sides hang up.
The other protocol available is UDP (User Datagram Protocol), this is comparable to posting a letter, you hope it reachs its destination, it usually does, but you can't be certain when. The advantage of UDP is it is very simple and doesnt require large bandwidth. This makes it ideal for small regular non-critical data packets.
So NMEA standards. The older NMEA0183 is pretty simple, it consists of preformated sentances with a header or prefix to describe the data following. NMEA0183 also uses an standard communcations bus called RS-422, this is a balanced line serial transmission bus, capable of long distance communications. It is electrically similar to RS-232 which is an unbalanced serial bus.
To convert RS-422 to ethernet all that is required is a serial to ethernet server, a small box that converts everything received on the serial port to Ethernet packets on the network port. Because NMEA0183 is RS-422 we can simply use a device like this
These are available for around £100 from various 3rd party retailers
So how do we get the Ethernet packets into our iPad app or PC Application? Easy, each application or vendor will specify a TCP or UDP Port that they expect to receive NMEA data on. So for iNavX this would be UDP port 2000. We therefore just have to setup the Serial to Ethernet Server to transmit the data using this protocol and port number. Thats it.
It is possible to use a RS-232 to Ethernet Server, and only connect 1 leg of the balanced RS-422 cable to the Serial Port. Electrically this will work, but you should refer to the vendors instructions and be aware of cable lengths and electrical noise. For robust use it is better all-round to take advantage of the balanced RS-422 bus.
This works with NMEA0183 (4800bps) and NMEA0183 High Speed (38400bps), simply setup the Serial to Ethernet server for the correct baud rate and you are done.
This is exactly what happens inside proprietary Marine Converters.
NMEA2000 & CANbus
The newer standard NMEA2000 can also be converted to Ethernet in a similar fashion using a CANbus to Ethernet Gateway. It is also possible to convert NMEA2000 to NMEA0183 and then use the above setup to make the conversion to Ethernet.
One thing we can be sure of, gradually vendors will be fitting Ethernet as a standard connectivty format - Furuno NavNET has been around for a while and the NMEA's OneNET is also being implemented. NMEA2000 & NMEA0183 will not disappear as there is still an important place for critical data with prioritisation, but we can be sure the standards will sit alongside each other now and for the future.
In summary, YachtSurfer and AIS NMEA data - no problem.