Broadcast Addressing; Unicast Addressing; Route Discovery - Digi XBee3 DigiMesh 2.4 User Manual

Networking

Broadcast addressing

All of the routers in a network receive and repeat broadcast transmissions. Broadcast transmissions
do not use ACKs, so the sending device sends the broadcast multiple times. By default, the sending
device sends a broadcast transmission four times. The transmissions become automatic retries
without acknowledgments. This results in all nodes repeating the transmission four times as well.
In order to avoid RF packet collisions, the network inserts a random delay before each router relays
the broadcast message. You can change this random delay time with the NN parameter.
Sending frequent broadcast transmissions can quickly reduce the available network bandwidth. Use
broadcast transmissions sparingly.
The broadcast address is a 64 bit address with the lowest 16 bits set to 1. The upper bits are set to 0.
To send a broadcast transmission:
Set DH to 0.
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Set DL to 0xFFFF.
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In API operating mode, this sets the destination address to 0x000000000000FFFF.

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.
If a device sends a unicast that uses both MAC and NWK retries and acknowledgments:
Use MAC retries and acknowledgments for transmissions between adjacent devices in the
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route.
Use NWK retries and acknowledgments across the entire route.
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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.

Route discovery

Route discovery is a process that occurs when:
1. The source node does not have a route to the requested destination.
2. A route fails. This happens when the source node uses up its network retries without receiving
an ACK.
Route discovery begins by the source node broadcasting a route request (RREQ). We call any router
that receives the RREQ and is not the ultimate destination, an intermediate node.
Intermediate nodes may either drop or forward a RREQ, depending on whether the new RREQ has a
better route back to the source node. If so, the node saves, updates and broadcasts the RREQ.
Digi XBee3® DigiMesh 2.4 RF Module User Guide
DigiMesh networking
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