Does LabView Telnet send any commands?

[CodeMunkee]

Situation:  Labview VI connects to a Verizon modem via Telnet to talk to a scientific instrument

Undesirable: when connection is broken (power to modem removed, cell carrier dropped) connection cannot be re-established.  Power must be cycled on the instrument.  It appears that either the modem or the VI sends something to the instrument that causes it to freeze when connection is broken.  I have verified this because when the Transmit Data port on the serial cable (modem to instrument) is disabled, the undesirable situation never occurs.

Question: my intuition tells me the modem is unhappy about something when the connection is broken, but to be thorough, is anyone aware of any commands LabView might transmit when connecting through Telnet?  Is there a better, maybe more robust, method of remote communication/telemetry thru LabView than Telnet?  Any suggestions are welcome, I'm not familiar at all with the details of telemetry and I'm clearly stumped.

Thanks.

[mishkin]

Hey CodeMunkee,

One suggestion that I have is if you're trying to figure out whether it's the VI that is sending certain packets through the router when the connection is broken, you should try taking a Wireshark capture on the TCP/IP packets being sent out. This will shine some light on what's going on down low and will hopefully tell you whether it's the VI or the modem sending those signals. Although, I am a little confused by how the modem can send/forward packets to the instrument after its power is turned off...

As far as the alternative methods of communcation with the instrument, I'd first have to ask for some details on what kind of instrument it is, etc. 

Something else that comes to mind is that maybe you can implement additional functionality within the VI that will check for the established connection with the modem (combination of System Exec and the Ping command?) before sending out any packets to the instrument. Hope this helps.