Link Status Transmission - Digi XBee 3 ZigBee User Manual

Transmission, addressing, and routing
Routing
approach
Ad hoc On-
demand
Distance Vector
(AODV) Mesh
Routing
Many-to-One
Routing
Source Routing
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 To revert from Many-to-One routing to AODV routing, a network must first do 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 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 determines the quality of a bi-directional link with each neighbor and
uses 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 +18 dBm, and the output power of device B is +3 dBm
(considerably less than the output power of device A). The link status messages might indicate the
following:
Digi XBee® 3 Zigbee® RF Module
Description
Routing paths are created between source and
destination, possibly traversing multiple nodes
("hops"). Each device knows where to send data next
to eventually reach the destination.
A single broadcast transmission configures reverse
routes on all devices into the device that sends the
broadcast.
Data packets include the entire route the packet
should traverse to get from source to destination.
RF packet routing
When to use
Use in networks that will
not scale beyond about
40 destination devices.
Useful when many
remote devices must
send data to a single
gateway or collector
device.
Improves routing
efficiency in large
networks (over 40
remote devices).
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