Transmission, addressing, and routing RF packet routing
Digi XBee® 3 Zigbee® RF Module
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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 transmits 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).
The following graphic is a 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 the
device transmits data from one node to its neighbor, it transmits an acknowledgment packet (Ack) in
the opposite direction to indicate that the transmission was successfully received. If the Ack is not
received, the transmitting device retransmits the data, up to four 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 traverses the same path the data traversed, but in the opposite direction. If the originator fails to
receive this Ack, it retransmits the data, up to two times until it receives an Ack. This Ack is called the
Zigbee APS layer acknowledgment.
Note Refer to the Zigbee specification for more details.
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