how do Xbees transfer serial data from router -> router -> coordinator ?

I currently working on a school project which I have to send serial data between a long distance devices. I used three xbee and has this sequence:

Xbee(router/end device) -> Xbee(router) -> Xbee(coordinator)

the middle xbee only acts like a transfer station which receives the data from the first xbee and then send to the coordinator.
the middle xbee currently attaching with a arduino board and programed the and send to serial.write() which works fine. Is there any way we could configure the middle xbee so it will acts the same way but without the arduino?

That depends on the model of radio you have. Digimesh and Zigbee can both relay packets exactly as you wish. All that is required in Digimesh or Zigbee is for that repeater radio to have power. You may also want to set the DH & DL settings on the end point and coordinator. by setting DH & DL to the SH & SL of the destination you will speed up your network and avoid sending data directly to the repeater.

Thanks. I’m using zigbee xbee s2
I set the DH DL on the end point Xbee to the repeater and set the DH DL on the repeater to the coordinator. i power up the repeater(middle xbee) without the arduino, the serial data won’t send through the repeater from end point xbee to the coordinator.