Specifications
XBee®/XBee‐PRO®SERFModules
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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.
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 configured
reverse routes on all devices into the device that
sends the broadcast
Useful when many remote devices must 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)