XBee‐PRO®900HP/XBee‐PRO®XSCRFModules
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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
unicast packet took. 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.
NACK Messages
The NACK API option of Tx Request Packets (see the API section of this manual for a description of the API
frames) provides the option to have a Route Information packet generated and sent to the originator of a
unicast when a MAC acknowledgment failure occurs on one of the hops to the destination. This information is
useful because it allows marginal links to be identified and repaired.
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