Advantech ADAM-4570W, Руководство пользователя, Страница: 34 / 62

ADAM-4570W & 4571W User Manual 28
RTS Threshold
RTS Threshold is the frame size above that an RTS/CTS handshake will
be performed before attempting to transmit. RTS/CTS asks for permis-
sion to transmit to reduce collisions, but adds considerable overhead. Dis-
abling RTS/CTS can reduce overhead and latency in WLANs where all
stations are close together, but can increase collisions and degrade perfor-
mance in WLANs where stations are far apart and unable to sense each
other to avoid collisions. If you are experiencing excessive collisions, you
can try turning RTS/CTS on or (if already on) reduce RTS/CTS Thresh-
old on the affected stations.
Fragmentation Threshold
Fragmentation Threshold is the maximum length of the frame, beyond
which payload must be broken up into two or more frames. Collisions
occur more often for long frames because sending them occupies the
channel for a longer period of time, increasing the chance that another
station will transmit and cause a collision. Reducing Fragmentation
Threshold results in shorter frames that "busy" the channel for shorter
periods, reducing packet error rate and resulting retransmissions. How-
ever, shorter frames also increase overhead, degrading maximum possi-
ble throughput, so adjusting this parameter means striking a good balance
between error rate and throughput.
Preamble
A preamble is a signal used in network communications to synchronize
the transmission timing between two or more systems. Proper timing
ensures that all systems are interpreting the start of the information trans-
fer correctly.