• By vjustme - edited: July 19, 2012

    In the official study guide it is refered for both 802.11a and 802.11g that 6,9,12Mbps  are OFDM required data rates. What does this mean? aren't the rest of supported data rates (18,24,36,48 and 54) utilizing OFDM too?

  • All are OFDM rates, but those required by the AP are called basic rates.  The AP mandates that stations joining the BSS support certain rates.  These rates are used for sending management frames and broadcast/multicast traffic to all stations.

    I believe the 802.11 standard establishes those rates you mentioned as the minimum required rates for any OFDM station.  An AP may add more rates to that list.

    There is another list of rates advertised by an 802.11 station called supported rates.  Support for these rates is not required to join a BSS, but a station may choose to transmit at any supported rate that the receiving station supports.  You'll often see the higher rates in this list.

    Separating rates into these sets allows for maximum throughput between stations that support high rates while maintaining compatibility for stations that may only support lower rates.

  • There is a technical difference between a "basic rate" and a "required rate".
    The required supported rates, according to the standard, are 6, 12, and 24 Mbps .   Each of these is the lowest rate in each of the first three modulation groups used in OFDM(i.e. the most robust) .
    Each is also a NON-punctured encoding (or as some would call them, a non-compressed code).  24 Mbps is the last, meaning highest, non-punctured rate.
    Punctured/non-punctured is NOT an administrator selectable option.  It is set for each of the rates.
    Administrators CAN usually set what the "basic" rates are on an AP. 

  • Wlanman -- a much better and accurate response.  Thanks!

  • By Howard - edited: August 20, 2012


    It really would have helped if industry and the IEEE would use a better choice of descriptors. 

    Basic, required, extended, supported, minimum, and more - enough to confuse just about anyone.

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