• Hi all,

    Don't know if I'm posting in the correct forum, but I'm currently looking why I have a bad wireless connection with my device and while analyzing, I noticed that the sequence of the information elements is not as it is specified by the IEEE specs.
    E.g. in the beacon frame I see that the RSN IE is listed before the Extended Supported Rates IE while the IEEE specs list the other way around.

    Does anyone know if this sequence is of any importance as listed in the IEEE specs?


  • Back in the day of super-slow processors, I might believe it would have mattered. But if the analyser can decode it, all should be well.

    Unless of course, the client can't process it in a different order. How old is this equipment, and is it from a reputable mfg ?

    I'm basing my answer on 20+ years of programming experience on this one, not as a Wi-Fi specialist, so please forgive me if I'm wrong.

    I would look to poor SNR, and/or interference first.

  • What Wlanman says sounds very reasonable. The IEEE 802.11 - 2007 spec gives a little bit of info:

    ?The frame body consists of the fields followed by the information elements defined for each management
    frame subtype. All fields and information elements are mandatory unless stated otherwise and appear in the
    specified, relative order. STAs that encounter an element ID they do not recognize in the frame body of a
    received management frame ignore that element and continue to parse the remainder of the management
    frame body (if any) for additional information elements with recognizable element IDs. A STA receiving a
    vendor-specific IE that it does not support shall ignore the vendor-specific IE. Unused element ID codes are
    Gaps may exist in the ordering of fields and elements within frames. The order that remains shall be

    ?A STA that encounters an unknown or reserved element ID value in a management frame received without
    error shall ignore that element and shall parse any remaining management frame body for additional
    information elements with recognizable element ID values. The frame body components specified for many
    management subtypes result in elements ordered by ascending element ID.?

    The specs pretty much say that we should stick to ascending order.


  • Think I know what might be going on here. If we look at Table 7.8 in the IEEE 802.11-2007 specs, we see a column on the left marked ?order?. Number 20 ( order sequence number ) is given as Extended Support Rates Order number 21 is given as Robust Security Network. That is, ESR first, then RSN next.

    However, when an analyzer is parsing a frame, it is most likely to look at the actual Information Element sequence.

    If we now look at Table 7.26 ( Element IDs ), we can now see that based on IE number, we have RSNIE as number 48 and ESRIE as number 50.

    In this case, we have RSN first and ESR next.

    Hence, although the ESRIE comes first in the beacon frame before the RSNIE, in terms of Information Element order, the RSNIE comes first, followed by the ESRIE.


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