Transmission, addressing, and routing
RF packet routing
XBee/XBee-PRO® S2C ZigBee® RF Module
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receive this Ack, it retransmits the data, up to 2 times until it receives an Ack. This Ack is called the
ZigBee APS layer acknowledgment.
Note
Refer to the ZigBee specification for more details.
Many-to-One routing
In networks where many devices must send data to a central collector or gateway device, AODV mesh
routing requires significant overhead. If every device in the network had to discover a route before it
could send data to the data collector, the network could easily become inundated with broadcast
route discovery messages.
Many-to-one routing is an optimization for these kinds of networks. Rather than require each device
to do its own route discovery, the device sends a single many-to-one broadcast transmission from the
data collector to establish reverse routes on all devices.
The many-to-one broadcast is a route request message with the target discovery address set to the
address of the data collector. Devices that receive this route request create a reverse many-to-one
routing table entry to create a path back to the data collector. The ZigBee stack on a device uses
historical link quality information about each neighbor to select a reliable neighbor for the reverse
route.
When a device sends data to a data collector, and it finds a many-to-one route in its routing table, it
transmits the data without performing a route discovery. Send the many-to-one route request
periodically to update and refresh the reverse routes in the network.
Applications that require multiple data collectors can also use many-to-one routing. If more than one
data collector device sends a many-to-one broadcast, devices create one reverse routing table entry
for each collector.
The ZB firmware uses the
AR
command to enable many-to-one broadcasting on a device. The
AR
command sets a time interval (measured in 10 second units) for sending the many to one broadcast
transmission. (See the command table for details).
High/Low RAM Concentrator mode
When Many to One (MTO) requests are broadcast, DO40 (bit6) determines if the concentrator is
operating in high or low RAM mode. High RAM mode indicates the concentrator has enough memory
to store source routes for the whole network, and remote nodes may stop sending route records
after the concentrator has successfully received one. Low RAM mode indicates the concentrator lacks
RAM to store route records, and that route records be sent to the concentrator to precede every
inbound APS unicast message. By default the device uses low RAM mode.
Source routing
In applications where a device must transmit data to many remotes, AODV routing requires
performing one route discovery for each destination device to establish a route. If there are more
destination devices than there are routing table entries, new routes overwrite established AODV
routes, causing route discoveries to occur more regularly. This can result in larger packet delays and
poor network performance.
ZigBee source routing helps solve these problems. In contrast to many-to-one routing that establishes
routing paths from many devices to one data collector, source routing allows the collector to store
and specify routes for many remotes.
To use source routing, a device must use the API mode, and it must send periodic many-to-one route
request broadcasts (AR command) to create a many-to-one route to it on all devices. When remote
devices send RF data using a many-to-one route, they first send a route record transmission. The