Specifications
XBee®/XBee‐PRO®SERFModules
©2009DigiInternational,Inc. 49
SampleRouteRequest(Broadcast)TransmissionWh ereR3isTryingtoDiscoveraRoutetoR6
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).
SampleRouteReply(Unicast)WhereR6SendsaRouteReplytoR3.
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
(MAC 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 (Nwk ACK) from the destination device. This ACK will traverse the same path that the data
traversed, but in the opposite direction. If the originator fails to receive this ACK, it will retransmit