Transmission, addressing, and routing RF packet routing
XBee/XBee-PRO ZigBee RF Modules User Guide 60
This example will use the transmit request API frame (0x10) to send an ASCII 1 in a broadcast transmission.
To send an ASCII 1 as a broadcast transmission, the following API frame can be used:
7E 00 0F 10 01 0000 0000 0000 FFFF FFFE 00 00 31 C2
Notice the destination 16-bit address is set to 0xFFFE for broadcast transmissions.
RF packet routing
Unicast transmissions may require some type of routing. ZigBee includes several different ways to route data,
each with its own advantages and disadvantages. These are summarized in the table below.
Note End devices do not make use of these routing protocols. Rather, an end device sends a unicast
transmission to its parent and allows the parent to route the data packet in its behalf.
Note A network cannot revert from Many-to-One routing to AODV routing without first doing a network reset
(NR).
Link status transmission
Before discussing the various routing protocols, it is worth understanding the primary mechanism in ZigBee for
establishing reliable bi-directional links. This mechanism is especially useful in networks that may have a mixture
of devices with varying output power and/or receiver sensitivity levels.
Each coordinator or router device periodically sends a link status message. This message is sent as a 1-hop
broadcast transmission, received only by one-hop neighbors. The link status message contains a list of
neighboring devices and incoming and outgoing link qualities for each neighbor. Using these messages,
neighboring devices can determine the quality of a bi-directional link with each neighbor and use that
information to select a route that works well in both directions.
For example, consider a network of two neighboring devices that send periodic link status messages. Suppose
that the output power of device A is +18dBm, and the output power of device B is +3dBm (considerably less than
the output power of device A). The link status messages might indicate the following:
This mechanism enables devices A and B to recognize that the link is not reliable in both directions and select a
different neighbor when establishing routes. Such links are called asymmetric links, meaning the link quality is
not similar in both directions.
Routing Approach Description When to Use
Ad hoc On-demand
Distance Vector (AODV)
Mesh Routing
Routing paths are created between source and
destination, possibly traversing multiple nodes
(“hops”). Each device knows who to send data to next to
eventually reach the destination.
Use in networks that will not scale
beyond about 40 destination devices.
Many-to-One Routing A single broadcast transmission configures reverse
routes on all devices into the device that sends the
broadcast.
Useful when many remote devices send
data to a single gateway or collector
device.
Source Routing Data packets include the entire route the packet should
traverse to get from source to destination.
Improves routing efficiency in large
networks (over 40 remote devices).
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