Connecting to a Cellular Modem

[rlvmaiden]

Hi,
I'm trying to connect to a PLC remotely over the internet. It's a SLC 5/03 connected via serial to a IPn4G cellular modem (Microhard). I'm having trouble connecting to the modem through RSLinx on my laptop, I've been told I just need to punch in the modem's IP address and listening port into RSLinx but I'm having trouble figuring out how to do this. I'm pretty new to this stuff, and would really appreciate any help I can get.
Thanks

 

[Ken Roach]

The usual way this works is that you have a software component on your PC that connects to the IP/Serial device (in your case, the Microhard modem) over IP, and presents a virtual serial port for use by your local PC software like RSLinx.

Rockwell Automation's serial drivers don't "tunnel across IP" themselves. Only a few expensive Ethernet/Serial devices like the Digi One IAP or Rockwell's 1761-NET-ENI are aware of the RA protocol and can unwrap the IP version and translate it to the serial version.

Does the Microhard documentation describe a virtual serial port utility ?

 

[CapinWinky]

Is the cellular modem always on? If not, you need to call it or it needs to call a central server first. I'm not familiar with Microhard cell modems, but in the ancient past of 2006 I put a machine into a plant in Turkey that I had to actually dial directly with my laptop's modem like direct dial-up.

I've also used **** boxes where I connect to the **** server using their software and they dial the modem and handle that side for me (way easier and probably what you're using). That gave me a VPN connection to the machine's subnet (and, if it was an AB PLC, would have had it show up in RSLinx).

 

[rlvmaiden]

This is from the spec sheet I could find, there's more but this looked the most relevant:

Serial Port Server:

-Extensive Serial Port Support:
TCP Server & Client / UDP Server & Client /
Modus / PPP / SMS / SMTP / AT command
-(2) Com Ports with Extensive
RS232/485/422 support

Firewall:

NAT, NAT-T VPN tunneling, port for-
warding, VPN/GRE pass-through;
Access control lists (IP/MAC filtering),
Data origin / integrity Authentication, DMZ

I thought that this Microhard modem should be able to take data from RSLinx over ethernet/internet and then send it to the PLC through the RS232 com port, but I take it that's not the case here?

 

[rlvmaiden]

Is the cellular modem always on? If not, you need to call it or it needs to call a central server first. I'm not familiar with Microhard cell modems, but in the ancient past of 2006 I put a machine into a plant in Turkey that I had to actually dial directly with my laptop's modem like direct dial-up.

I've also used **** boxes where I connect to the **** server using their software and they dial the modem and handle that side for me (way easier and probably what you're using). That gave me a VPN connection to the machine's subnet (and, if it was an AB PLC, would have had it show up in RSLinx).

The PLC is really the only thing at the site. If we need to do any work on it, we want to be able to bring the cell modem to site and then have the programmer do the work from wherever he's at, then go disconnect the modem and bring it back when we're done. I called tech support for Microhard and I was told that to connect to the modem, I just need to enter in the modem's IP and listening port on my end and I'm good to, no VPN or anything needed.

 

[diat150]

to do what you want with a serial plc, like Ken said, I think you will need to use a digi one iap or some other terminal server like a digi one sp that supports virtual comm ports. You would then do a 1:1 nat in the cell modems router configuration.

Or you could buy a digi connect wan modem that has that functionality built in.

 

[Ken Roach]

The way they're describing the modem working is that you would need a software program that sends the exact same bytes to a TCP port using IP protocol that it would send to an ordinary serial COM port.

Some software does that. Some does not. RSLinx does not.

That's why the vast majority of serial/IP device vendors use a virtual serial port emulator.

Since Microhard evidently doesn't publish a user manual on their Internet website, it's up to you as their customer to get one and find out if it describes how to use a virtual serial port through their modem.

In addition, I'm very annoyed at their "just type in an IP and a port" approach. Industrial device security ? Never heard of it !

 

[Saffa]

In addition, I'm very annoyed at their "just type in an IP and a port" approach. Industrial device security ? Never heard of it !

"No one will ever try and attack this nuclear centrifuge" - A (Late) Iranian Systems Engineer.

It's actually scary how many such open systems there are out there. Found an internet router at a plant a couple months back with admin HTTP port open on the WAN side, and still using default "admin, admin" username and password. A slightly talented 12 year old with the modem user manual could have broken in and caused all sorts of havoc.