• Hi,

    I was wondering about how a Qos AP with short AIFs, say around length of a Pifs or even a Sifs, using short slot times, would affect its neighbors.

    Lets say we have 2 APs and create a scenario similar to the Meru vs Cisco test, except this time its me and my neighbor.

    My AP is QoS capable with AIF less than a Difs,as mentioned above, using EDCA. My neighbors none QoS AP uses short time slots with Difs during contention for DCF. The AIFS and DIFS values are used after CCA before backoff, for respective APs. Say we each have 2 STA associated to our APs. His are both none qos STA, and mine are one qos STA and one none qos station. If the APs were to compete for the medium on the same channel, as we are neighbors, could my QoS AP have an advantage for throughput, within the standards when communicating with my none QoS STA, when compared to my neighbors none QoSAps throughput to his none QoS STA?

    I am just basing this example on AIFs not so much changes on CWmin or CWmax, time limit of txop(which i assume the AP assigns to itself) and such.
    Does the QoSAP revert to DCF DIFS when contending to transmit before the backup period if its downstream communication is with a none QoS client?

    An addendum,
    I realize that the minimum idle delay and CWmin and CWmax parameters can be different for ACs but since there are no default values listed a vendor could make AIFs value the same for all ACs--- My Pifs or Sifs length in the example above or use a SIFS value for AC_VO and AC_VI, and PIFS (sifs + 1 slot) for AC_BE and AC_BK. This also raises another question as to how the QoSAP views non QoS traffic.

    Anyhelp is appreciated,

  • Rico, an interesting article on Cisco vs Meru;jsessionid=CX3A3BIQQAAXEQSNDLPSKHSCJUNN2JVN?articleID=195900045

    Gino G

  • Gino,

    Tks for the info. Actually that article was what got me to think about this scenario.
    Its always enlightening to find the piece of the puzzle that i am missing in these scenarios.

    Good luck with your wireless studies


  • Looking over the 802.11e standard document i found the following

    .......all directed frames that are sent to a nQSTA by a QAP shall not use frame formats associated with QoS.

    Thus the AIFs would not be used in this scenario, as this value is derived from frames with the QoS frame format. This is good news as my neighbor will still consider me a friend, if we find ourselves in the scenario listed above.

    To make things clearer it is also mentioned ..... in delivering an MSDU to a nQSTA the QAP will use the appropriate access category to that UP.

    I rhetorically wonder, if you were to assume all of my clients in the example above are QSTAs, can the AC parameters be set such that downstream normal data from the QAP will give a higher throughput rate than my neighbor transfering normal data from his nQAP to nQSTA, when we share the same channel for contention? In this situation you can use the QoS frame types and thus i would imagine the AIFS for the appropriate AC.


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