User Manual

Operation
RFI-9256 Radio Modem User Manual Page 21 of 96
FRAME TIME
The frame time is the amount of time that the RFI-9256 will spend on each channel in the hopping pattern.
This is also referred to as the channel dwell time. The frame time can be adjusted to suite a particular
application. The set of values are shown in Table 7.
Frame Time Bytes per Packet Throughput (One Way) Throughput (Total)
5ms 5 8kbps 16kbps
8ms 26 26kbps 52kbps
10ms 41 32kbps 64kbps
15ms 77 41kbps 82kbps
20ms 113 45kbps 90kbps
25ms 149 48kbps 96kbps
30ms 185 49kbps 98kbps
35ms 221 51kbps 102kbps
Table 7: Frame time configuration
Selection of frame time will trade off maximum throughput against latency. A low frame time will decrease
both latency and throughput, while a high frame time will increase both latency and throughput. This is
discussed in the section Latency Reduction on page 24.
DIRECTIONAL BIAS
A single frame on the RFI-9256 contains two packets, one from the master and one from the slave. In the
default configuration the size of both packets is the same, so the system is unbiased. In many systems data
will flow in one direction substantially more than in the other direction. When this is the case the RFI-9256
can be configured to bias its frames so that the master packet and slave packet are of different lengths.
In order to configure a link for directional bias, one radio must be set to the outgoing radio, and one to the
incoming radio. The link from the outgoing radio to the incoming radio has more bandwidth, while the link
from the incoming radio to the outgoing radio has its bandwidth reduced.
Table 8 shows the different settings that can be obtained through directional bias.
Frame
Time
Outgoing Bytes
per Packet
Incoming Bytes
per Packet
Outgoing
Throughput
Incoming
Throughput
5ms 5 5 8kbps 8kbps
8ms 26 26 26kbps 26kbps
10ms 55 27 44kbps 22kbps
15ms 125 28 67kbps 15kbps
20ms 197 28 79kbps 11kbps