Xbee Digimesh 2.4 Transmission Timeouts; Unicast One Hop Time; Transmitting A Broadcast; Transmitting A Unicast With A Known Route - Digi XBee User Manual

XBee DigiMesh 2.4 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 parameters, 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

• Transmitting a unicast with an unknown route
• Transmitting a unicast with a broken route.
Note The timeouts in this section are theoretical timeouts and not precisely accurate. The
application should pad the calculated maximum timeouts by a few hundred milliseconds.
When using API mode, Tx Status API packets should be the primary method of determining if a

Unicast one hop time

A building block of many of the calculations presented below is the unicastOneHopTime. As its
name indicates, it represents the amount of time it takes to send a unicast transmission between two
adjacent nodes. It is largely dependent upon the mac retry setting (RR). DigiMesh networks assume
that the average number of mac level retries across a multi-hop wireless link will be three or less. It is
defined as follows:
RR (mac retries)
0
1
2
3
Transmitting a broadcast
A broadcast transmission must be relayed by all routers in the network. The maximum delay would
be when the sender and receiver are on the opposite ends of the network. The NH, NN, and MT
parameters define the maximum broadcast delay as follows:
BroadcastTxTime=NN*NH*(MT+1)*18ms
Transmitting a unicast with a known route
When a route to a destination node is known, the transmission time is largely a function of the
number of hops and retries. The timeout associated with a unicast assumes the maximum number
of hops is necessary (as specified by NH). The timeout can be estimated in the following manner:
knownRouteUnicast=2*NH*MR*unicastOneHopTime
XBee/XBee-PRO DigiMesh 2.4 User Guide
Unicast One Hop Time
unicastOneHopTime = 5 ms
unicastOneHopTime = 24 ms
unicastOneHopTime = 40 ms
unicastOneHopTime = 63 ms
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