Send serial data from industrial gateway to end node

Dear all,

we have wrote a python application that run on the Xbee industrial gateway.

The gateway collect data from several end node and some time the gateway have to interact with the end node send them back info (in particular the gateway send sync message in order to setup and reset the RTCC that run on the end node).
At the moment in order to send message form router to the end node we use the API function that pass trough the remote manager server. This solutions unfortunately is not suitable for us since the processing of the message strongly depends on the speed of cellular connection.
We would like to know if exist a solution in order to send serial data to the end node from the gateway without using the API of remote manager.
Can you point out to an example or indicate a link where a solutions is explained?

Thanks in advances for your support.

Best regards
Filippo Ambroglini