Operation
RFI-9256 Radio Modem User Manual
Page 28 of 109
Frame
Time
(ms)
Outgoing
Bytes per
Packet
Incoming
Bytes per
Packet
Outgoing
Throughput (kbps)
Incoming
Throughput (kbps)
Over the
air
Serial
Over
the air
Serial
5
5
5
8
10
8
10
8
26
26
26
32.5
26
32.5
10
55
27
44
55
22
27.5
15
125
28
67
83.75
15
18.75
20
197
28
79
98.75
11
13.75
25
269
28
86
107.5
9
11.25
30
338
31
90
112.5
8
10
35
410
31
93
116.25
7
8.75
Table 8: Directional bias configuration for different frame times
RETRIES
The maximum number of retries per frame can be configured between 0 to 255. When a low number of
retries is selected, the link may become unreliable in the presence of interference. When a high number of
retries is selected the link will be reliable, however it may induce substantial latency in the presence of
interference.
If an RFI-9256 is given data to transmit to a slave that is non-existent, either due to a misconfigured
destination address, the slave being out of range, or the slave unit being faulty, then it will transmit each
frame the maximum number of retries. This can dramatically slow down the throughput of a radio network.
The RFI-9256 also supports exponential back-off and retry. This mechanism is intended for a situation
where there are multiple slaves that may have data to transmit at the same time. If these slaves are
configured with exponential back-off and retry mode enabled, collisions will have a minimal impact on
system performance.
For more information on configuring back-off retries, see section B.1.1 on page 71.
SYNCHRONISATION
When two or more RFI-9256 are located in very close proximity, such as when they are in a back-to-back
repeater configuration, the transmitter from one can interfere with the receiver of the other even though they
are on different channels, simply due to the large amount of power that is being radiated.
In order to prevent this from happening it is desirable to synchronise the radios so that they will transmit at
the same time. Only master units can be synchronised in this way, as slave units must obtain their
synchronisation from the network master.
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