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I have a very good (100%) WiFi, wireless-signal as reported by the DIR-655 (router / AP ) to the client/adapter.

The router reports the client-connection speed to be 241M or 214M or 268M.

  • Why don't those router-reported speeds conform to speeds shown in the MCS Index tables

  • And with Short GI(enabled , checked) i.e. 400ns) set in the DIR-655 wireless/advanced configuration why or how would the router connect at or report speeds (data-rates) associated with the Long-GI(800ns) rates in the MCS-tables ?

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... Ok, may be wrong here as I haven't even heard of that MCS table before, however, I would take an educated guess that those speeds are simply under perfect lab conditions with no outside interference at all. In addition to that being perfect conditions, throughput is something that is very hard to accurately measure - it is possible that it does not take account of TCP overhead (re-transmision/dropped/error frames etc.). –  William Hilsum Aug 4 '12 at 21:53
    
thnx for reply . but, like most here ( I suppose ), I can hypothesize as well as the next "educated-guesser". I believe, this really is a question for the actual "device-firmware-developers" for the described router ... who would know the algorithms used to compute the connection-rate. AFIK: The router reports/updates to the possible-MAX connection-rates as it receives/interprets signals ... (refer to MCS tables ) ... the local wifi adapter would report the actual throughput-speeds. But, re-read my OP for the real-questions ... –  OldTechy Aug 5 '12 at 6:02

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It seems telling that the three rates you listed are each exactly 2 megabits/sec slower than the top three HT40, Long-GI, 2 spacial streams rates: 216, 243, and 270. It suggests they have a bug in their display code, but it seems strangely arbitrary that they'd all be off by two.

As for the guard interval, enabling short GIs doesn't necessary require them (unless the UI or the user's manual tells you otherwise). It's also possible that the clients are choosing long GIs for whatever reason. Most UIs for Wi-Fi devices don't make it clear whether a given rate is the rate the AP is using when sending to that client, or the rate that client is using when sending to the AP. They are not required to be the same, and often are not the same.

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