Use cases

• Determine whether or not the RT target can connect to other Internet hosts
• Validate the connection by checking the returned string from the web service

Features

• Attempts to open an HTTP connection to the Microsoft NCSIMicrosoft Network Connectivity Status Indicator, a web service that returns the string “Microsoft NCSI”. web service, read the returned string and compare to the expected string “Microsoft NCSI”
• Code runs on either the RT target or PC host without modification
• Use as a stand-alone VI or incorporate the code directly into your block diagram

Keep in mind

• Requires the “HTTP Client with SSL Support” Academic RIO Device software set add-on
• If your application does not otherwise require HTTP services, use the alternative TCP-based Internet access check method which simply checks if it is possible to connect to the NCSI service

LabVIEW block diagram elements

Locate these elements with "Quick Drop" (press Ctrl+Space and start typing the name); click on an icon to see more sample code that uses that element:

Example code

• Connect your Academic RIO Device to your PC using USBLAN, Ethernet, or Wi-Fi. NOTE: Not all Academic RIO Devices have Ethernet and Wi-Fi connectivity options.
• Download and unpack the rt_check-internet-access-http.zip (for use with NI myRIO 1900) or the NIELVISIII-rt_check-internet-access-http.zip (for use with NI ELVIS III) archive, and then double-click the ".lvproj" file to open the project. NOTE: This project was written for a NI myRIO 1900 or NI ELVIS III connected by USBLAN at IP address 172.22.11.2. If you are using a different IP address or another Academic RIO Device (Example: NI myRIO 1950 or NI RIO Control Module) do the following:
  • If using the NI myRIO 1950 or NI RIO Control Module start with the NI myRIO 1900 Archive.
  • Different IP address: Right-click on the "NI myRIO 1900" Device, choose "Properties", and then enter the new IP address
  • Different device:
    • Right-click on the top of the project hierarchy, select "New Targets and Devices", keep the "Existing target or device" option, and then find and select your particular device
    • Select all of the components under the "NI myRIO 1900" device: click the first one and then shift+click the last one
    • Drag the selected components to the new device
    • Right-click the "NI myRIO 1900" device and select "Remove from project"
• Run “RT Main” and “PC Main” and observe the following:
  • Each VI executes the same subVI “check internet access (http).vi” once every five seconds and displays its result as the “Internet OK” Boolean indicator
  • Each VI also executes the same subVI “show available IP addresses.vi” once every half second and displays its results
  • Click the “dot-decimal notation?” control to switch between the machine name and the IP address
  • If you are using the USB cable to establish the network link between the Academic RIO Device and the PC, you should observe that the PC is host #1 (172.22.11.1) and the RT is host #2 (172.22.11.2) on the USBLAN network 172.22.11.0
  • “PC Main” will likely show other networks such as your wireless connection
  • “RT Main” will also show address 127.0.0.1 (“localhost”) – this address is for loopback testing and is internal to the RT target (in fact, every network host has its own loopback address)
• Enable the Academic RIO Device wireless connection to a consumer-grade wireless router (press the Device wireless button if connection was established earlier) while “RT Main” is running:
  • A third IP address appears
  • If your wireless connection provides Internet service (e.g., with your consumer-grade wireless router) you can expect to see the “Internet OK” indicator activated
• Try disabling your PC network connection to see the “Internet OK” indicator go out

Expected results

Developer walk-through

Outline

• “check Internet access (http)” VI
  • “GET” VI sends web request to the Microsoft “Network Connectivity Status Indicator” web service
  • Conclude Internet access is OK when returned webpage body is the string “Microsoft NCSI”
  • Case structure implements standard error behavior
  • Same VI runs without modification on RT or PC
• RT Main
  • Process Loop #1: run “show available IP addresses” VI every half second
  • Process Loop #2: run “check Internet access (http)” VI every five seconds
  • Use local variable technique to stop both process loops from one button
  • PC Main – same code as “RT Main”
• Stop parallel process loops
  • Use local variable
  • Set mechanical action of “stop” button to “Switch When Pressed”

For more information

1. Appendix K: Network Connectivity Status Indicator and Resulting Internet Communication in Windows Vista (https://technet.microsoft.com/en-us/library/cc766017)
   A complete discussion of the Microsoft NCSI web service.
   
2. "check internet connection" thread on NI Community Forum (http://forums.ni.com/t5/LabVIEW/check-internet-connection/td-p/1724074)
   The original idea for the example code presented here.
   

Related content

Tags:

• networking
• IP address
• dot-decimal notation
• web service
• NCSI
• HTTP
• stopping parallel loops

Targets:

• RT
• PC

LabVIEW VIs and block diagram elements:

• HTTP Get