• What are the two types of QoS provided by 802.11e?

  • I have some question regarding the inconsistency of the QoS explanation.

    The Intel's white paper describes that the task group e produces the new HCF which can operate in two modes: EDCAF and HCCA. To my understanding, EDCAF is the prioritised QoS based on enhancement of the DCF (using different classes of traffic) while HCCA is the parametrised QoS based on enhanced PCF (ability for AP to step in even in CP).

    Now the study guide (3rd ed) clearly states that EDCAF is DCF+QoS (i can accept this) while HCF is PCF+QoS. This is the bit that i find contradictive with Intel's paper.

    The question is then, is HCF = EDCAF and HCCA (that is, HCF is a summary of EDCAF and HCCA) or is it EDCAF and HCF?

    The second question, is my understanding of EDCAF being a prioritised QoS while HCCA a parametrised QoS correct? or that is a wrong classification (ie. parametrised QoS can be EDCAF or HCCA depending on how they are implemented).

    Can someone clarify? am I understanding it wrong or the study guide was not correct?

  • Hi cgo,

    The study guide is wrong in saying HCF = PCF + QoS.

    By the way, EDCAF is the coordination function itself, where as EDCA is the channel access method. It is correct to call it EDCA in this context. Here is what the standard itself says:

    9.1.3 Hybrid coordination function (HCF)
    The QoS facility includes an additional coordination function called HCF that is only usable in QoS network (QBSS) configurations. The HCF shall be implemented in all QSTAs. The HCF combines functions from
    the DCF and PCF with some enhanced, QoS-specific mechanisms and frame subtypes to allow a uniform set of frame exchange sequences to be used for QoS data transfers during both the CP and CFP. The HCF uses
    both a contention-based channel access method, called the enhanced distributed channel access (EDCA) mechanism for contention-based transfer and a controlled channel access, referred to as the HCF controlled
    channel access (HCCA) mechanism, for contention-free transfer.

    EDCA is always prioritized QoS, and HCCA is always parameterized QoS.

    Thanks for pointing out this error in the study guide. We will add it to the errata sheet.



  • Hi,

    Thanks for great QoS resources - it's an area I've had great confusion in.

    BTW the latest errata (12June06) still don't cover this area.

    CWNA ed.3 book P.381 doesn't seem to relate WMM back to EDCAF and HCF. This might be helpful.

    The book doesn't seem to mention,
    Prioritized QoS
    Parameterized QoS

    as specific concepts unless I missed it.
    If that's right, would the PWO-100 exam still expect these as the amswer to the original question in this thread?
    I would have answered the original question,
    What are the two types of QoS provided by 802.11e?


    Would this be wrong and,
    Prioritized QoS
    Parameterized QoS
    be correct?

    Thanks, MH

    Regards, MH

  • Hi Mark,

    Parameterized and Prioritized are correct. The CWNA study guide (v3) didn't really go into QoS (by design) because the exam objectives do not.

    The next revision of exam objectives (and study guide) will go into much more detail on QoS (802.11e). The current exam is written to the current objectives.


  • Read the latest edition of the IEEE 802.11 handbook for a good outline/definition of QoS for 802.11 networks.

    Considering I have done some enterprise level QoS in the past the wireless stuff, though good is still somewhat of a kludge of timers.

    Well we will get there some day.


  • Hi,

    Could I be so bold as to suggest the Subject for the "Question of the Week" have some indication as to the topic?

    "Question of the Week - Qos, 802.11e"

    Obviously there are some very informative discussions triggered by these questions and they can be found more easily this way.

    Eg. If I open the Forum "CWAP, Troubleshooting, Configuration and Performance Issues" and do a text-search for "qos" it is easily found.

    Regards, MH

Page 1 of 1
  • 1