Changes between Version 9 and Version 10 of 802.11/MAC/Lower/Retransmissions


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Timestamp:
May 5, 2015, 11:18:31 AM (9 years ago)
Author:
chunter
Comment:

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  • 802.11/MAC/Lower/Retransmissions

    v9 v10  
    1313* ''dot11LongRetryLimit'' = 4
    1414
    15 === Glossary of Terms ===
     15=== Reading the Figures ===
     16
     17[[Image(legend.png)]]
     18
     19The figures below are not drawn to scale. The presence of the events shown in the legend above is used to indicate only their existence and not their relative size to one another. Furthermore, the presence of a backoff interval is not shown as increasing in duration with an increasing contention window. In fact, it is important to keep in mind that any given random draw of a backoff can produce a 0-duration backoff. The figure will show this event with the full backoff event regardless.
    1620
    1721||= '''Term''' =||=  '''Definition'''  =||
    … …  
    2226||  '''CW'''  ||  Contention Window  ||
    2327
     28The above table summarizes the terms used in the figures below.
    2429
    25 [[Image(legend.png)]]
     30----
    2631
    2732= Short MPDUs (MPDU length ≤ ''dot11RTSThreshold'') =
    … …  
    5863  '''''Excerpt of Section 9.3.4.4 of 802.11-2012'''''
    5964
    60   ''After transmitting a frame that requires acknowledgment, the STA shall perform the ACK procedure, as defined in 9.3.2.8. The SRC for an MPDU of type Data or MMPDU and the SSRC shall be incremented every time transmission of a MAC frame of length less than or equal to dot11RTSThreshold fails for that MPDU of type Data or MMPDU. This SRC and the SSRC shall be reset when a MAC frame of length less than or equal to dot11RTSThreshold succeeds for that MPDU of type Data or MMPDU.''
     65  ''After transmitting a frame that requires acknowledgment, the STA shall perform the ACK procedure, as defined in 9.3.2.8. The SRC ... and the SSRC shall be incremented every time transmission of a MAC frame of length less than or equal to dot11RTSThreshold fails ... . This SRC and the SSRC shall be reset when a MAC frame of length less than or equal to dot11RTSThreshold succeeds ... .''
    6166
    6267In other words, the SRC increments because of the MPDU transmission failure. The SSRC increments because the SRC increments. The CW increases because the SSRC increments. When an ACK is received in the second attempt of MPDU 1, Section 9.3.4.4 dictates that the success of that MPDU causes the SRC and the SSRC to be reset. Section 9.3.3 dictates that the successful delivery of the MPDU also resets the CW.