TCP/IP instabilities in LabVIEW?

I'm just beginning to work with TCP/IP in LabVIEW and I'm hitting some problems. As usual the hardest part is knowing what questions to ask.
Background: Essentially, we have a PC (Windows 7) running LabVIEW (2011), communicating with a Staubli CS8 robot controller. The code on the controller is written using Staubli's native VAL3 development environment. It's set up so that we send it pre-defined command strings via TCP/IP. The robot performs the command and when it reaches its destination it sends a response string.
If I use Putty to send the strings via command line, everything works fine, and I get the response string expected loud and clear afte the robot has performed its task. If I use LabVIEW, however, using code based on the TCP 'active' and 'passive' example functions, I get communication most of the time, but occasionally the system hangs.
The robot almost always get the movement command - this is obvious as it starts moving. The problem seems to be more to do with the fact that the 'listening' portion of the LabVIEW code seems to be occasionally missing the string sent back to the PC, and the listen loop then runs indefinitely, thereby causing the system to hang.
Using timeouts as a quick fix is out as the robot speed can be varied, therefore there is no way to know exactly when the robot is going to send back its message to the PC (although it's always going to be on the order of seconds).
So my initial questions are:
1.) Is a degree of instability normal in communications using TCP/IP?
2.) Why does LabVIEW appear to be less stable than Putty?
3.) Does anybody have TCP example VIs that I can contrast with the two examples that ship with LabVIEW?

I can only support Julianne's statements. I have done quite a few intensive network communication libraries and projects and don't see instabilities as you describe them, if the LabVIEW part is programmed correctly. Network communication I have done include both TCP/IP and UDP based protocols and also binary and ASCII style variants of those.
Network programming is different than other LabVIEW programming in several ways. You have to be prepared that network functions can return errors for many reasons, and that some of them should be ignored, some of them indicate to retry the operation, and some require you to close and reopen the connection. Which error means what, is the biggest part of the magic about network programming and there are no definitive rules about this, as it can depend on the used protocol, the particular implementation of the remote side and sometimes other factors you need to figure out.
With some experience you learn to program fault tolerant network communication, that can work with different implementation specific behaviour of the remote side but this stage can sometimes feel a bit like magic and the only way to get it to work right is usually by trial and error, and some logical thinking about what the different network layers are supposed to do.
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions

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Hi everyone,i am currently trying to communicate with two computers at the moment using TCP/IP.I have done a simple server and client VI but the server doesnt seem to be writing the string im trying to send and it also gives an error message
Error 1 occurred at TCP Write in Server.vi
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LabVIEW: An input parameter is invalid. For example if the input is a path, the path might contain a character not allowed by the OS such as ? or @.
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Attachments:
Server.vi ‏13 KB
Client.vi ‏13 KB

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TCP-IP.JPG ‏62 KB

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How best to receive large short array --- tcp, socket, LabVIEW, ShortBuffer

The application in question works with a LabVIEW program via Ethernet (a tcp connection). The LabVIEW program generates a large (e.g. 600x600) array of numbers (either 32-bit floats or 16-bit signed ints, whichever we choose). The question is what is the fastest, reliable, way to get those numbers? LabVIEW can send it two ways, the first is to convert the array to a string, the second is just to send the array data as-is. I believe that converting to string inflates the size of the message so much that this is not a good option. So I guess my question is how to receive the array of numbers (either as 32-bit floats or 16-bit signed ints)?
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theHandOfTheKing wrote:
The application in question works with a LabVIEW program via Ethernet (a tcp connection). The LabVIEW program generates a large (e.g. 600x600) array of numbers (either 32-bit floats or 16-bit signed ints, whichever we choose). The question is what is the fastest, reliable, way to get those numbers? LabVIEW can send it two ways, the first is to convert the array to a string, the second is just to send the array data as-is. Text is more likely to be reliable as you will be able to read the data to see when something has gone wrong and have a better idea of why.
I believe that converting to string inflates the size of the message so much that this is not a good option. Why do you believe this? Do you have a bandwidth or time limit you haven't mentioned?
So I guess my question is how to receive the array of numbers (either as 32-bit floats or 16-bit signed ints)?You can optimise the data send later after you get something working.
I was thinking of using a FloatBuffer or a ShortBuffer. The latter would be best since floats do not get us any extra information in this case, so I do not know why I even bothered to consider using them. Not sure why float would have less information.
Okay, rambling, do you think a LabVIEW array of shorts will be able to get read by a ShortBuffer on the other end of a TCP connection? Provided the data is only shorts, its ideal.
Also, am I going to have to call read() multiple times in order to get all the elements of the array?yes.

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