I want to access a remote set of equipment by using a *** single *** GSM modem point-of-entry. Next, I want to communicate to several different equipments located nearby, all RS-232.

The modem has an RS-232 interface; I can use a set of addressable modems, creating a bus on RS-422 that will be able to separately call each of the sub-systems, one-at-a-time. The principle involved is, next to the gsm modem there is the master RS-232/RS-422 converter, then there's the bus, and all the sub-systems are "hanging" on that bus, providing that each has its own slave RS-422/RS-232 addressable modem.

The thing is, how do I access all of them directly? Does anyone know any manufacturer that provides adequate equipment for this purpose, or any *** better *** solution?

 

Have a look at the Black Box site and check out a Code-Operated Switch (RS-232 & RS-422) 4-Port and 8-Port this enables you to Control up to eight serial devices—RS-232 or RS-422— from your PC but may also be able to do what you want.

Search for "Code-Operated Switch" on the Black Box site http://catalog.blackbox.com/BlackBox/Templates/blackbox/mainscreen.asp

Hope this helps.
Mark Mullins.