XBee®/XBee‐PRO® ZB SMT RF Modules
network (refer to the Broadcast Transmission), each node that re-broadcasts the message updates the path
cost field and creates a temporary entry in its route discovery table.
Sample Route Request (Broadcast) Transmission Where R3 is Trying to Discover a Route to R6
When the destination node receives a route request, it compares the ‘path cost’ field against previously received
route request commands. If the path cost stored in the route request is better than any previously received, the
destination node will transmit a route reply packet to the node that originated the route request. Intermediate
nodes receive and forward the route reply packet to the source node (the node that originated route request).
Sample Route Reply (Unicast) Where R6 Sends a Route Reply to R3.
Note: R6 could send multiple replies if it identifies a better route.
Retries and Acknowledgments
ZigBee includes acknowledgment packets at both the Mac and Application Support (APS) layers. When data is
transmitted to a remote device, it may traverse multiple hops to reach the destination. As data is transmitted
from one node to its neighbor, an acknowledgment packet (Ack) is transmitted in the opposite direction to
indicate that the transmission was successfully received. If the Ack is not received, the transmitting device will
retransmit the data, up to 4 times. This Ack is called the Mac layer acknowledgment.
In addition, the device that originated the transmission expects to receive an acknowledgment packet (Ack)
from the destination device. This Ack will traverse the same path that the data traversed, but in the opposite
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DCD [ DIGITAL CORE DESIGN ]
