Digi XBee XTC User Manual page 34

Networking methods
With mesh networking, the distance between two nodes does not matter as long as there are enough
nodes in between to pass the message along. When one node wants to communicate with another,
the network automatically calculates the best path.
A mesh network is also reliable and offers redundancy. For example, If a node can no longer operate
because it has been removed from the network or because a barrier blocks its ability to communicate,
the rest of the nodes can still communicate with each other, either directly or through intermediate
nodes.
Note Mesh networks use more bandwidth for administration and therefore have less available for
payloads.
Unicast addressing
When devices transmit using DigiMesh unicast, the network uses retries and acknowledgments
(ACKs) for reliable data delivery. In a retry and acknowledgment scheme, for every data packet that a
device sends, the receiving device must send an acknowledgment back to the transmitting device to
let the sender know that the data packet arrived at the receiver. If the transmitting device does not
receive an acknowledgment then it re-sends the packet. It sends the packet a finite number of times
before the system times out.
The MR (Mesh Network Retries) parameter determines the number of mesh network retries. The
sender device transmits RF data packets up to MR + 1 times across the network route, and the
receiver transmits ACKs when it receives the packet. If the sender does not receive a network ACK
within the time it takes for a packet to traverse the network twice, the sender retransmits the
packet.
To send unicast messages while in Transparent operating mode, set the DH and DL on the
transmitting device to match the corresponding SH and SL parameter values on the receiving device.
Routing
A device within a mesh network determines reliable routes using a routing algorithm and table. The
routing algorithm uses a reactive method derived from Ad-hoc On-demand Distance Vector (AODV).
The firmware uses an associative routing table to map a destination node address with its next hop. A
device sends a message to the next hop address, and the message either reaches its destination or
forwards to an intermediate router that routes the message on to its destination.
XBee®/XBee-PRO XTend Compatible (XTC) DigiMesh RF Module User Guide
Delivery methods
34