User's Manual
9XTend™ OEM RF Module - Product Manual v2.x6x
© 2010 Digi Internatonal, Inc. 56
To send Unicast messages, set the DH and DL on the transmitting module to match the corre-
sponding SH and SL parameter values on the receiving module.
Broadcast Addressing
Broadcast transmissions will be received and repeated by all nodes in the network. Because ACKs
are not used the originating node will send the broadcast four times. Essentially the extra trans-
missions become automatic retries without acknowledgments. This will result in all nodes repeat-
ing the transmission four times as well. In order to avoid RF packet collisions, a random delay is
inserted before each node relays the broadcast message. (See NN parameter for details on chang-
ing
this random delay time.) Sending frequent broadcast transmissions can quickly reduce the
available network bandwidth and as such should be used sparingly.
The broadcast address is a 64 bit address with the lowest 16 bits set to 1. The upper bits are set to
0. To send a broadcast transmission set DH to 0 and DL to 0xFFFF. In API mode the destination
address would be set to 0x000000000000FFFF
Routing
A module within a mesh network is able to determine reliable routes using a routing algorithm and
table. The routing algorithm uses a reactive method derived from AODV (Ad-hoc On-demand Dis-
tance Vector). An associative routing table is used to map a destination node address with its next
hop. By sending a message to the next hop address, either the message will reach its destination
or be forwarded to an intermediate node which will route the message on to its destination. A
message with a Broadcast address is bro
adcast to all neighbors. All receiving neighbors will
rebroadcast the message and eventually the message will reach all corners of the network. Packet
tracking prevents a node from resending a broadcast message twice.
Route Discovery
If the source node doesn’t have a route to the requested destination, the packet is queued to
await a route discovery (RD) process. This process is also used when a route fails. A route fails
when the source node uses up its network retries without ever receiving an ACK. This results in
the source node initiating RD.
RD begins by the source node broadcasting a route request (RREQ). Any node that receives the
RREQ that is not the ultimate destination is called an intermediate node.
Intermediate nodes may either drop or forward a RRE
Q, depending on whether the new RREQ has
a better route back to the source node. If so, information from the RREQ is saved and the RREQ is
updated and broadcast. When the ultimate destination receives the RREQ, it unicasts a route reply
(RREP) back to the source node along the path of the RREQ. This is done regardless of route qual-
ity and regardless of how many times an RREQ has been seen before.
This allows the source node to receive multiple route replies. The source node selects the route
with the best round trip route quality, which i
t will use for the queued packet and for subsequent
packets with the same destination address.
RF Module Configuration
Two command mode protocols are supported by this DigiMesh version of the 9XTend RF Module:
AT Command Mode - Printable protocol that is intended for manual entry of commands and
viewing parameter values.
API Operation - Binary protocol intended for programmatic transmissions and receptions of
data packets. For example, using API mode, sequential packets can be sent to different
addresses without having to escape into command mode and change DL between each trans-
mission.
AT Commands
To Send AT Commands (Using the 'Terminal' tab of the X-CTU Software):