Why does remote connectivity through a cell modem to a LI-COR eddy covariance system work from certain Internet connections and not from others?
LI-COR eddy covariance systems can have several devices which use the TCP/IP protocol, and they can all be connected to a modem which has access to the Internet. A port forwarding rule is set up in the modem, so that communications arriving through certain ports are forwarded to specific instruments. For example, the LI-7200RS CO2/H2O analyzer communicates over ports 7200 and 22, the LI-7700 CH4 analyzer communicates over port 7700, and the Sutron logger communicates over port 23. A port forwarding rule should be set up in the modem, such that communications arriving at the modem through port 7200 are forwarded to the LI-7200RS, and not another device.
Some university and office networks, as well as Internet service providers, may block communications over certain ports for security reasons. The best solution to this problem is to obtain a list of ports that are not blocked by your IT department or service provider, and use those ports in your port forwarding rule. Another way to check to see if you can access certain ports from within your network is to use the website http://portquiz.net. You can add the port number after a colon, along with the site name. For example, to check port 7200, you simply type http://portquiz.net:7200 in the address bar on your browser. If the port is open, you will see a confirmation that indicates you have a successful connection.
In certain cases, a firewall can block programs from communicating through certain ports, so in those cases, the tests using portquiz.net may work, as this is tested through a browser, but the software may still not communicate. In this case, you should contact your IT department to ensure that exceptions are made in the firewall for the analyzer interface software for the LI-7200RS/LI-7500RS, and LI-7700 interface software, and the Xterm.exe software for communicating with the Sutron data logger.