RTS/CTS Exchange in Hidden Node Problem ( 802.11 MAC Layer)















The Duration field of the RTS frame carries a NAV setting to cover the CTS response plus the time needed for the subsequent frame exchange. The CTS response has its Duration field set to the Duration field value seen in the RTS less SIFS and the duration of the CTS response itself.
In the diagram, the hidden node (STA 3) would receive the CTS frame and set its NAV to defer for the subsequent frame exchange.

STA 2 sees both the RTS and CTS.

The RTS/CTS exchange is required when the length of a data or management frame exceeds the threshold. (dot11RTSThreshold)
The dot11RTSThreshold is a local management attribute and may be set to 0 so that all MPDUs are delivered with an RTS/CTS exchange, to the maximum allowed MPDU length so that the RTS/CTS need not be used at all, or any value in between.















From the figure above we can find that
RTS duration = SIFS + CTS + SIFS + Data time + SIFS + ACK time
CTS duration = SIFS + Data time + SIFS + ACK time

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