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There is an acknowledgement (ACK) between two nodes during a Unicast. There is none for broadcasting. Hence, Unicast is the preferred method of transferring data between nodes. On the autopilot, the Xbee receiving address is hardcoded into a define located in the networking code. The data relay is configured to send packets to the address it received it from (still via unicast).
The modules are also configured to use the Point to Point/Multipoint delivery method. Xbee's also support the Repeater/Directed Broadcast and Digimesh methods, which are ways of leveraging multiple nodes to act as repeaters to increase range. Because we only fly with 2 nodes, one on the ground and one on the plane, this functionality is not used.
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The Destination Address fields are configured on the PicPilot, and are not important for the Xbee connected to the aircraft. This is also not important for the data relay, as it sends packets to the address it received them from.
MAC/Physical Layer Settings
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