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TCP speed problem when changing from read to write

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Hi all,

 

I have a fairly bizarre problem with the TCP/IP blocks in labview. I'll take a moment to explain my set up.

 

I have a laptop running Labview 7.1 and a RT ETS machine running the standard Labview RT software. The two are linked with a dedicated ethernet connection, not a crossover, but ran through a network switch which has nothing else plugged into it.

 

I have 2 vis, a server vi which runs on the RT machine and a client vi that runs on the laptop. All these do is transfer a small amount of data back and forth. The client sends a DBL to the server vi, this number is multiplied by 3, has 1 added to it then sends it back. The client then sends a string to the server, followed by a stop byte. (see attached).

 

What I am finding is that this loops at an incredibly slow rate of ~200ms. This is a 100Mbps ethernet connection! I have tried many things and can't work out why and I'm hoping someone can help me. It seems to be that there is some delay when the direction of data is changed (i.e. a read after a write)

Here is where it gets silly. When I remove the send string and the stop boolean from both vis, the whole thing runs very very swiftly indeed.

 

This is part of a larger, complex, project that I'm having trouble with and I've narrowed it down to this issue. I've checked the boards and no one else seems to be having this problem, which would suggest that I'm doing something silly

 

Please help!

 

Pete

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Accepted by topic author Hungry_Pete
Take a look at this thread about the Nagle algorithm, which addresses what I suspect is the same issue you're seeing.
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