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802.11 Reference Design: Frame Retries

An important role of the 802.11 DCF is to detect the presence of transmission failures and properly recover from those errors through the use of a retransmission mechanism. This behavior is subtle and often misunderstood. This document serves two roles:

  1. To describe the behavior implemented in the Mango 802.11 Reference Design.
  2. To defend the behavior with references to the 802.11 standard.

The organization of this document is a series of examples that build on one another and show corner cases in the behavior. The retransmission mechanism in 802.11 is further complicated by the presence of RTS/CTS medium reservation handshakes prior to the transmission of an MPDU, so examples are broken up into sections depending on whether RTS/CTS is not used (i.e. an MPDU is "short") or RTS/CTS is used (i.e. an MPDU is "long"). Without loss of generality, the examples in this document assume the following parameters:

  • dot11ShortRetryLimit = 7
  • dot11LongRetryLimit = 4

Glossary of Terms

Term Definition
SRC Short Retry Count
LRC Long Retry Count
SSRC Station Short Retry Count
SLRC Station Long Retry Count
CW Contention Window

Short MPDUs (MPDU length ≤ dot11RTSThreshold)

Example S.1

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