Siemens PLC via Cellular

We succeeded in getting a Siemens S7-226 with CP243 and PPI serial up on the Digi Connect WAN, which is a cellular router for GSM or CDMA with local Ethernet and serial port.

In Summary:

• To talk to S7-226 by serial PPI, you need a newer Siemens PC-to-PPI cable - the older one doesn't work. I am not sure why, but that is what we found. Using Digi RealPort we enabled a redirected COM port to the remote Digi Connect WAN's serial port, which is connected to the PPI port of the S7-200. We then defined a radio modem port within MicroWin using that COM port. Although a 30 second timeout would be ideal, MicroWin only gives options for 1, 10 or 100 seconds of timeout. You should probably select the 100 seconds to minimize your comm costs. Now MicroWin or Step7 can freely connect to and reprogram the S7-200. The high end-to-end latency of the cellular IP networks makes the performance pretty sluggish when compared to direct serial, but it works.
• To talk to S7-315 by serial MPI, you need the special Siemens PC-to-MPI cable. Just as with the S7-200, we set up a redirected Digi RealPort, however we did NOT need to fool Step7 into thinking this was a radio modem. It just worked fine as is when given longer timeout settings.
• To talk to CP243 by S7 protocol over ISODE on Ethernet, we enabled TCP port forwarding of port 102 on the Digi Connect WAN to the CP243 module. The CP243 is configured to treat the Digi Connect WAN as its Gateway IP. This also worked fine as is when given longer timeout settings.