[Chris Hibner]

I ran a test using UDP two days ago and I wasn't very happy with the results - perhaps one of the NI guys could say if what I saw is typical or not.

I set up a test program to communicate via UDP from a laptop to the cRIO. The laptop was set up to countinuously count up and the value of the counter was passed to the cRIO via UDP. I read the received counter value while in debugging mode in LabVIEW.

The issue is this: if the data wasn't immediately received on the cRIO, the data was queued and was then read eventually in the original order that it was sent. For example, the counter on the laptop would be counting through 200 and the received packet on the cRIO would be paused at 180 for a second. Then, when the cRIO started receiving packets again, it would start counting up again from 181 even though the laptop was now on 220. For a real-time system, I would expect that all missed/delayed packets would be ignored and the most recent packet would be read.

This is a real problem if I'm trying to receive target aim and distance data from the image processing on a remote computer. I have no idea how much delay there is from what I'm receiving to when it was sent. If some delay occurs, I could be off by X seconds for the remainder of the match.

I ran the same experiment with TCP and did not see this issue.