AIS Position Error?
 

Agreed. I use UDP in my stuff.

Raymarine's E-80 and their Sirius weather interface also appear to be using
UDP for all traffic. The E-80 also sends other data, I saw a fair number of
packets before I even had the Sirius unit attached. Didn't bother sniffing
the packets with ethereal though. Come winter when I've got the units out
of the boat I may try decoding what gets sent around.

It makes it easy to keep the network
"open" in that any device on the subnet can grab the data and use it.
For that reason, I just send the NMEA sentences one at a time, with no
mods or higher level constructs that a listener would have to be aware
of. The only "gotcha" (and it's irrelevant to the vast majority of
uses) is that all the routers I've looked at block UDP broadcasts from
going off the subnet, for good and sufficient reasons. If you want to
broadcast to another subnet you have to target the UDP to a specific
address on that subnet and let it repeat the message as a broadcast on
that subnet. At least, that's the way I solved the problem in my
stuff.

Yep, UDP is great for all the reasons you mention, including isolation on
the local subnet.

Unfortunately, I've found that most of the potential listeners to the
NMEA data I'm making available are so busy making everything
proprietary that this is less of a benefit than I hoped.

Two steps forward, two steps back. Yeesh.

-Bill Kearney

AIS Position Error?
 

On Fri, 1 Sep 2006 09:45:56 -0700, "Paul" wrote:

Thank you for this information. I don't know what equipment was used on the
ship I encountered, but this is a completely plausible explanation for what
I was seeing. Perhaps I will try to locate the ship owner and send them a
message -- it couldn't hurt!

If they are using the Furuno GP80 or GP90 it's quite likely. I found about
30% of vessels around here use those GPS models and about 1/3 of them were
"cheating" by putting their paper chart offsets into their GPS, thereby
causing the problem.

What port were you in when you discovered this problem?

It was Labuan, a small island off the coast of Borneo.

Dave