Rssi Indicators; Xbee Network Discovery; Neighbor Polling; Link Reliability Of The Xbee Digimesh 2.4 Rf Module - Digi XBee User Manual

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XBee/XBee-PRO DigiMesh 2.4 User Manual
Send an Explicit Addressing Command API frame (0x11) using 0x12 as the cluster ID and 0xE8
as the source and destination endpoint. Data packets received by the remote will be echoed back
to the sender.

RSSI Indicators

It is possible to measure the received signal strength on a device using the DB command. DB
returns the RSSI value (measured in –dBm) of the last received packet. The DB value only
indicates the received signal strength of the last hop. If a transmission spans multiple hops, the
DB value provides no indication of the overall transmission path, or the quality of the worst link.
It only indicates the quality of the last link and should be used sparingly. The DB value can be
determined in hardware using the RSSI/PWM module pin (pin 6). If the RSSI PWM functionality
is enabled (P0 command), when the module receives data, the RSSI PWM is set to a value based
on the RSSI of the received packet. (Again, this value only indicates the quality of the last hop.)
This pin could potentially be connected to an LED to indicate if the link is stable or not.

XBee Network Discovery

The network discovery command is used to discover all Digi modules that have joined a network.
Issuing the ND command sends a broadcast network discovery command throughout the
network. All devices that receive the command will send a response that includes the device's
addressing information, node identifier string (see NI command), and other relevant information.
This command is useful for generating a list of all module addresses in a network.
When a device receives the network discovery command, it waits a certain amount of time
before sending its own response. The maximum time delay is set on the ND sender with the NT
command. The ND originator includes its NT setting in the transmission to provide a delay
window for all devices in the network. Large networks may need to increase NT to improve
network discovery reliability. The default NT value is 0x82 (13 seconds).

Neighbor Polling

The neighbor poll command can be used to discover the modules which are immediate neighbors
(within RF range) of a particular node. This command is useful in determining network topology
and determining possible routes. The command is issued using the FN command. The FN
command can be initiated locally on a node using AT command mode or by using a local AT
command request frame. The command can also be initiated remotely by sending the target
node an FN command using a remote AT command request API frame.
A node which executes an FN command sends a broadcast to all of its immediate neighbors. All
radios which receive this broadcast will send an RF packet to the node that initiated the FN
command. In the case where the command is initiated remotely, responses are sent directly to
the node which sent the FN command to the target node. The response packet is output on the
initiating radio in the same format as a network discovery frame.

Link Reliability of the XBee DigiMesh 2.4 RF Module

For a mesh network installation to be successful, the installer must be able to determine where
to place individual XBee devices to establish reliable links throughout the mesh network.
© 2014 Digi International Inc. 29