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Settings for RTS Threshold and Fragmentation Threshold

Are you familiar with the settings for RTS Threshold and Fragmentation Threshold and what direction to adjust for reducing collisions and a wireless network. Is it better to adjust at the base station or at the client side?

RTS Threshold is the frame size above which an RTS/CTS handshake will be performed before attempting to transmit. RTS/CTS asks for permission to transmit to reduce collisions, but adds considerable overhead. Disabling RTS/CTS can reduce overhead and latency in WLANs where all stations are close together, but can increase collisions and degrade performance in WLANs where stations are far apart and unable to sense each other to avoid collisions (aka Hidden Nodes). If you are experiencing excessive collisions, you can try turning RTS/CTS on or (if already on) reduce RTS/CTS Threshold on the affected stations.

Fragmentation Threshold is the maximum length of the frame, beyond which payload must be broken up (fragmented) 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 collision. Reducing Fragmentation Threshold results in shorter frames that "busy" the channel for shorter periods, reducing packet error rate and resulting retransmissions. However, shorter frames also increase overhead, degrading maximum possible throughput, so adjusting this parameter means striking a good balance between error rate and throughput.

This was first published in September 2004

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