Request from coordinator to router(end device), ways of it

Good morning!
I have several units of industrial eqipment which use RS232 as communication port. So I can plug in to each unit and recieve data from specific sensors by using special requests (machine request).

I want to make Xbee network with one Coordinator and several Routers (according to number of units).
Right now I don` understand how to separate answers from routers, I imagine two ways:

  1. in cycle Xbee API change DH and DL of coordinator and make requests, after it wait response.
    Make cycle depend of quantity of routers.

  2. Make my own requests, which contains specific machine answer and special identifier of router. On side of unit I will put arduino or something like this which will add this identifier to the message of unit.

  3. Maybe there is some less difficult way to understand who sent message to coordinator?

Sure, try just setting the DL and DH to the node you want to send the data to. Then send your commands. That node will be the only one to receive the command so that device connected to it will be the only one to respond. Then change the DL and DH to the next and do the same thing over again.