Transmission Timeouts - Digi XBee-PRO XSC Manual

XBee‐PRO® 900HP/XBee‐PRO® XSC RF Modules
MAC retries/acknowledgments are used for transmissions between adjacent nodes in the route. NWK
retries/acknowledgments are used across the entire route.
To send Unicast messages, set the DH and DL on the transmitting module to match the corresponding SH
and SL parameter values on the receiving module.
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 Distance Vector). An
associative routing table is used to map a destination node address with its next hop. By sending a mes-
sage to the next hop address, either the message will reach its destination or be forwarded to an interme-
diate router which will route the message on to its destination. A message with a broadcast address is
broadcast to all neighbors. All routers receiving the message will rebroadcast the message MT+1 times and
eventually the message will reach all corners of the network. Packet tracking prevents a node from resend-
ing a broadcast message more than MT+1 times.
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 router that receives the RREQ that
is not the ultimate destination is called an intermediate node.
Intermediate nodes may either drop or forward a RREQ, 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 quality 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 it will use for the queued packet and for subsequent packets with the
same destination address.
Throughput
Throughput in a DigiMesh network can vary by a number of variables, including: number of hops, encryp-
tion enabled/disabled, sleeping end devices, failures/route discoveries. Our empirical testing showed the
following throughput performance in a robust operating environment (low interference).
200 kbps version, 115.2 kbps serial data rate, 100 KB
Note: Data throughput measurements were made setting the serial interface rate to 115200 bps, and measuring the time
to send 100,000 bytes from source to destination. During the test, no route discoveries or failures occurred.

Transmission Timeouts

When a node receives an API TX Request (API configured modules) or an RO timeout occurs (modules configured for
Transparent Mode) the time required to route the data to its destination depends on a number of configured param-
eters, whether the transmission is a unicast or a broadcast, and if the route to the destination address is known.
Timeouts or timing information is provided for the following transmission types:
• Transmitting a broadcast
• Transmitting a unicast with a known route
© 2014 Digi International Inc.
Configuration
Mesh unicast, 1 hop, Encryption Disabled
Mesh unicast, 3 hop, Encryption Disabled
Mesh unicast, 6 hop, Encryption Disabled
Mesh unicast, 1 hop, Encryption Enabled
Mesh unicast, 3 hop, Encryption Enabled
Mesh unicast, 6 hop, Encryption Enabled
Data Throughput
91.0 kbps
32.5 kbps
16.7 kbps
89.3 kbps
32.2 kbps
16.1 kbps
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