• Except in the case of Broadcast packets, I doubt that you can definitely say what will happen.   I would bet that it would always wait at least one full DTIM interval before throwing it away, regardless of the LI setting. 

    Remember that a client knows an AP's DTIM interval before it connects to it.  So if it sets its LI shorter than that, you could argue that it would be setting itself up for losing packets if the AP did anything else.

    I'm sure most AP manufacturers figured this out a long time ago. 

  • OK i have one more scenario. DTIM = 2 and LI = 4. Before sending DTIM AP has buffered broadcast data and unicast data for STA. Now how BC and UC data is sent.

  • No problem in this case.   It will be handled normally, at the end of the DTIM period.

    Because its Broadcast data it's never ACKed, and if the client doesn't get it, it's lost. Exactly what the standard says will happen.

  • Agree with howard. 

    This is normal case. 

  • By Howard - edited: May 25, 2016

    I've come to the conclusion that part of my original problem with the concept of Listen Interval, was caused by its name.

    Beacon Interval.  DTIM Interval. These are both called intervals !

    The  Listen Interval should have been called the Listen LIMIT or the Listen DURATION, or the Listen MAXIMUM.   Take your pick.

    Poorly named features, in connection with poor descriptions, create misunderstanding.

    I'm not picking on the Standard,  the problem exists in many situations.  Somebody was just too enamored with the word INTERVAL.

  • I agree with howard & pawan regarding BC data, but I think i didn't explain the scenario properly.

    DTIM = 2 & listen interval = 4. DTIM is sent and STA receives it. 

    Now DTIM indicates that both BC data & Unicast data is buffered at AP for STA. Now AP will start sending BC data to STA. Once BC data transmission is over how unicast data is sent to STA. Wether STA will send PS-poll immediately to AP after the BC data transmission is over or STA will go back to sleep and wait till it's listen interval. 

  • It is up to the logic in the client.

    It can be different for every device, AND even the specific settings in the device when it is configured- either at the manufacturer, the installer, or the particular user.

    Some customers may be more interested in Power Savings than others

  • A usecase where you can see BC is, in case of broadcast ARP. If you ping a doze/sleep STA from another STA, the buffering of the BC ARP can be seen.

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