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Thread: Ack frames airtime usage question.

  1. #1

    Default Ack frames airtime usage question.

    Hi Guys me again.

    As I plunge deeper in to the wonderful world of 802.11 and Eye P.A I have noticed that with some Eye P.A captures, I am seeing roughly the same amount of ack frames as data frames from an individual client (one assumes this is good). I have also noticed that the ack frames although similar in quantity to the data frames, are smaller than data frames yet take up vastly more airtime. Why is this? Do I have a design problem.

    The only explanation I can offer is that the time the medium needs to be reserved for, according to the duration field in the data frame, is being incorporated into the ack frames. Am I right?

    Thanks

    Simon

  2. Default

    Quote Originally Posted by svosper View Post
    Hi Guys me again.

    As I plunge deeper in to the wonderful world of 802.11 and Eye P.A I have noticed that with some Eye P.A captures, I am seeing roughly the same amount of ack frames as data frames from an individual client (one assumes this is good). I have also noticed that the ack frames although similar in quantity to the data frames, are smaller than data frames yet take up vastly more airtime. Why is this? Do I have a design problem.

    The only explanation I can offer is that the time the medium needs to be reserved for, according to the duration field in the data frame, is being incorporated into the ack frames. Am I right?

    Thanks

    Simon
    Hi Simon,

    You are exactly right! Excellent detective work.

    This is actually going to change in the next update.

    Originally, we were trying to develop a tool that would represent the air time of what a client may experience at any location. Now for a little explanation of how we got there and where we are going. We had noticed that some 802.11 devices were setting the duration to the maximum length always. We thought that was problematic and we wanted to display that visually. Since there is not a subframe type for unnecessarily reserved airtime, we lumped it into the ACK (unfortunately). Eye P.A. is also adding in a contention window value with no preference to the type of subframe. That is exceptionally problematic.

    The duration and CW calculations are not appropriate to add into the calculation because 1, CW applies to clients individually but not to the packets being sent. That means during the time a client backs off another client could begin to transmit. This has been fixed and will be available in the next update. 2. The duration values were also being applied to the ACK subframes. Eye P.A. now does a best effort with the duration values and has heuristics built in to determine if another client device transmits during that duration to subtract it out. The airtime will still be applied to the ACKs.

    Send me an email, I'd be happy to discuss this a little further and I would like to hear your feedback anyway.

    -Trent

  3. #3

    Default

    Hi Trent

    Thanks for the response. Where do I find your email address?

    Thanks

    Simon

  4. Default

    Quote Originally Posted by svosper View Post
    Hi Trent

    Thanks for the response. Where do I find your email address?

    Thanks

    Simon
    Hi Simon,

    Email me at support@metageek.net, and I'll forward you to Trent.

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