Error 56 occurred at TCP Open Connection

[DBISI]

Hello, looking for a little advice.

I have been working with a telnet project that has been working for several days, until all of a sudden it crashed. I rebooted the PC and it still failed. But then it started working on it's own all of a sudden.

While it was not working,I found the error was at the very beginning of my telnet when it was just trying to open the connection before any processing.

I was getting a time out error with a 5 second timeout.

Has anyone seen this before and is there a way to reset the TCP in such a situation?

[rolfk]

That is usually happening for one of two reasons:

1) your server machine on the TCP/IP network is unreachable (or your computer got disconnected due to a cable or router error).

2) The server you try to connect too, is hung up. Either fully or it is still serving your previous connection that you lost through the crash but it takes the server some time to realize that there is no-one anymore on the other side.

[DBISI]

Interesting. I am talking to a few wi-fi networks, and I think what I am fighting is the signal dropping out.

There is nothing programmatically that can be done to re-set the TCP in case of such an error?

When I was trouble shooting it earlier, it managed to fix itself over time. However, it failed before I came in today so I don't know how long it was in error, and Ideally, I wouldn't want them in error for too long. I even tried a PC reboot and that didn't solve the issue.

[DBISI]

Let me ask this:

Is there a reason why I couldn't connect to a Numato device using TCP connect if I can immediately ping the device just fine?

I try to open the connection, it fails, and I immediately ping it. I attempt this 3 times and all 3 times it fails to connect but will ping just fine.

I wonder if something in LabVIEW needs addressing.

[billko]

---

@DBISI wrote:

Let me ask this:

Is there a reason why I couldn't connect to a Numato device using TCP connect if I can immediately ping the device just fine?

I try to open the connection, it fails, and I immediately ping it. I attempt this 3 times and all 3 times it fails to connect but will ping just fine.

I wonder if something in LabVIEW needs addressing.

---

The only thing a successful ping guarantees is that the network card can be reached.  Probably a far better solution is to keep sending some kind of simple command, e.g., a command to return information on the instrument.  When you get the response you are expecting, the instrument is very likely ready to use.

[DBISI]

How do I send a command if I can't open the connection?

[rolfk]

Ping operates on the IP layer (specifically ICMP but that is technically pretty much IP). TCP is an entire layer higher.

- Are you using the right port number?

- Did you check your LabVIEW application is not blocked in the Windows firewall for the network group (public, domain, private) your IP address belongs to?

- Or some other firewall setting disallowing certain port ranges?

[billko]

---

@DBISI wrote:

How do I send a command if I can't open the connection?

---

Sorry, I didn't read your post properly and I failed to see that you need to open a TCP connection.

[crossrulz]

---

@rolfk wrote:

- Are you using the right port number?

I am pretty certain Numato uses a Telnet connection (it has been several years since I touched on of their devices). Therefore, the port should be set to 23.

[DBISI]

It's all good.

I am using port 23. It connects 99% of the time. So I don't think it's a Windows/Firewall issue. Also note, all my IP's are static.

The issue I am having is it seems to fail every now and then, and takes a minute or two to correct itself before it opens again. That is what I am trying to figure out...

It seems to be one of two issues: The Numato itself or my code. And since my code opens 99% of the time, it seems unlikely. But the failure to open seems like a LabVIEW problem.

I have my full application running on the other PCS. on my test PC, I made this simplified code that all it does is scan and do nothing else. See attached. It fails the same as the other PC's. Which implies its not LabView but the Numato.

If it's the Numato, there isn't much I can do.