© 2014 Digi International Inc. 32
XBee/XBee-PRO
®
DigiMesh 2.4 User Manual
Trace Routing
In many applications it is useful to determine the route which a DigiMesh unicast takes to its
destination. This information is especially useful when setting up a network or diagnosing
problems within a network. The Trace Route API option of Tx Request Packets (see the API
section of this manual for a description of the API frames) causes routing information packets to
be transmitted to the originator of a DigiMesh unicast by the intermediate nodes.
When the Trace Route API option is enabled, and a unicast is sent to destination radios, the
radios then forward the unicast to its eventual destination and transmit a Route Information (RI)
packet back along the route the unicast originator. A full description of Route Information API
packets can be found in the API section of this manual. In general they contain addressing
information for the unicast and the intermediate hop for which the trace route packet was
generated, RSSI information, and other link quality information.
Example: Suppose that a data packet with trace route enabled was successfully unicast from
radio A to radio E, through radios B, C, and D. The following sequence would occur:
• After the successful MAC transmission of the data packet from A to B, A would output a RI
Packet indicating that the transmission of the data packet from A to E was successfully for-
warded one hop from A to B.
• After the successful MAC transmission of the data packet from B to C, B would transmit a RI
Packet to A. A would output this RI packet out its serial interface upon reception.
• After the successful MAC transmission of the data packet from C to D, C would transmit a RI
Packet to A (through B). A would output this RI packet out its serial interface upon reception.
• After the successful MAC transmission of the data packet from D to E, D would transmit a RI
Packet to A (through C and B). A would output this RI packet out its serial interface upon
reception.
It is important to note that Route Information packets are not guaranteed to arrive in the same
order as the route taken by the unicast packet. It is also possible for the transmission of Route
Information packets on a weak route to fail before arriving at the unicast originator. Because of
the large number of Route Information packets which can be generated by a unicast with Trace
Route enabled it is suggested that the Trace Route option only be used for occasional diagnostic
purposes and not for normal operations.
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