Operation
RFI-9256 Radio Modem User Manual
Page 25 of 109
Framing delays:
Framing delays will occur depending on where data arrives relative to the start of
a frame. Consider the situation in Figure 9.
Frame 1
Frame 2
Frame 3
Frame Time
20ms
P1
P2
Figure 9: Data arriving at different times relative to the start of frame
The data arriving at P1 would be transmitted almost immediately in frame 2, while the data arriving
at P2 will have to wait until the start of the next frame. In the worst case, the amount of latency
introduced will be equal to the frame time.
Link quality:
The quality of a link can have a substantial impact on the latency induced by the
radio. The RFI-9256 will retry frames that become corrupted due to RF interference, configurable
between 0 and 255 retries. The more retries that are required to get a packet through the greater the
latency induced. Each retry adds an additional frame time to the latency induced by the radio.
DATA TIMING
The RFI-9256 will change the inter-character and inter-packet timing of data that it transmits as all data
received by the RFI-9256 is framed for transmission over the air. Consider the situation shown in Figure 10.
Frame 1
Frame 2
Frame Time
20ms
P1
P3
P1
P2
P2
P2
P3
Inter-character Delay
Figure 10: Data timing variation due to framing
Data between P1 and P2 arrives before the start of Frame 1. This is then transmitted over the air, and is
output at the end of Frame 1. The data between P2 and P3 had to wait for frame 2 to be transmitted, so now
there is an artificial gap introduced between the bytes before P2 and after P2.
