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IEEE 802.11 defines several physical layer data rates to provide more robust communication by falling back to a lower rate in the presence of high noise levels. The choice of the current rate can be automatized; e.g., Auto-Rate Fallback (ARF) is a well-known mechanism in which the sender adapts its transmission rate in response to link noise using up/down thresholds. ARF has been criticized for not being able to distinguish MAC collisions from channel noise. It has however been shown that, in the absence of noise and in the face of collisions, ARF does not play a significant role for TCP's downlink performance. The interactions of ARF, DCF and uplink TCP have not yet been deeply investigated.
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