Terminal server? (Kinda.)

[Michael ODonnell]

> We're going to have cash registers on-site -- good ol' RS-232
> connections.  We're also getting software that can talk to these
> computers.
> [...]
>[Register] <- RS-232-to-USB -> [Wall Wart] <- VPN -> [Home office computer]


Trying to read between the lines here: your situation is constrained by
your need to run some inflexible software on the "Home office computer"
machine (a Windows box?)  that was never expected to talk to a cash
register via anything except (say) COM1, yes?

So, your choices for a solution would seem to be limited to either:

 - emulating an RS-232 port directly on the "Home office computer" such
   that (say) COM3 was secretly one endpoint of a relay scheme, or

 - having some other system nearby that offers a physical RS-232
   connection and which then relays that traffic for you.

In that second case (which might be more straightforward in some respects)
your diagram might instead look like this:

 [Register] <- RS-232-to-USB -> [Wall Wart] <- VPN -> [Wall Wart] <-> USB-to-RS-232 <-> [Home office computer]


What kind of traffic is going over that RS-232 connection?

Do we care about the control lines or are the Tx/Rx lines enough?