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Thread: Max rate problem

  1. #1

    Default Max rate problem

    I just installed a replacement router (Asus RT-AC68U-1900). I set up my old Linksys ea6500 as an AP. Using InSSIDer 4.0 I was getting max rates on the 2.4 at 450 and 5Ghz at 2106. Then I upgraded to the latest version of IS 4.0 (4.2.109) and my max rates went down in half.

    Here is what I am getting:
    ea6500 (AP):
    2.4Ghz; ch 1; bgn; 450; 5.0ghz: ch 157/155; n/ac; 1300

    AC68U:
    2.4Ghz; ch 11; bgn; 216.7; 5.0Ghz; ch161/155; n/ac; 1300

    I am getting better max rates with the AP ea6500 on the 2.4Ghz. Any ideas?

  2. #2
    Join Date
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    You've encountered a reporting issue - there is no 2106 - along with a bunch of hype.
    First, an 802.11ac access point can signal at a rate of 433 mbit per spatial stream under laboratory conditions. Thus, 1300 mbit is for 3 spatial streams.
    Second, your device typically can handle only 1 or 2 streams.
    Finally, a max rate is just a theoretical number with little real world meaning. (Like a speed limiter on a German car of 155 mph driving on a US highway.)
    Old Mod by the Sea

  3. #3

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    Thanks for the reply. However, the 216.7 on my main router seems to not be optimal.

  4. #4
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    What it reports for a max rate is inconsequential. Ignore max rate reporting. It is the actual throughput that counts.
    Not all routers/APs are the same. Only the high end commercial units are 4 x 4. Many aren't even 3 x 3 capable.
    How many antennas do your APs have? What level of QAM do they use?
    Old Mod by the Sea

  5. #5

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    I've searched and do not see a way to close this post, but I request no further action. Thanks

  6. #6

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    Hi kenepp1,

    Quote Originally Posted by kenepp1 View Post
    Using InSSIDer 4.0 I was getting max rates on the 2.4 at 450 and 5Ghz at 2106. Then I upgraded to the latest version of IS 4.0 (4.2.109) and my max rates went down in half.
    There were some bugs in the way that we calculated max data rates, and we fixed them a few versions ago. You now have a more recent version that fixes the data rate bugs.

    I was getting max rates on the 2.4 at 450 and 5Ghz at 2106. Then I upgraded to the latest version of IS 4.0 (4.2.109) and my max rates went down in half.
    There is a lot of confusion around what maximum data rates are, and how they are determined, especially with 802.11ac. I checked out the product page for the EA6500, and found a lot of confusion on the page itself. In one place, it claims 450mbps + 1300mbps, and in the tech specs, says that the max link rate is only 867mbps.

    The actual data rate depends on a few factors:
    1. How many spatial streams (1x1, 2x2, 3x3, or 4x4) the device has
    2. What guard interval (short or long) is in use
    3. What channel width (20, 40, or 80 MHz) is in use

    You can see a chart showing all of these different conditions and data rates here.

    In the 2.4 GHz band, you probably have and are using:
    1. 3 spatial streams (although I couldn't find a spec sheet showing how many radio chains this router has)
    2. A short guard interval
    3. A 40 MHz channel (40 MHz channels don't work well in 2.4 GHz, we recommend always turning them off)

    This all adds up to a max data rate of 450 mbps. Note that in the real world, you'll never achieve 450 mbps, that's just the max signaling rate. At best, you'll only hit about 60 percent of of the max signaling rate. With a 3x3 device like a MacBook Pro, you'll only hit about 270 mbps in actual throughput, if conditions are insanely perfect in every way. With a 1x1 device like an iPhone or tablet, you'll only hit about 43mbps in actual throughput. It's all about the limitations of the client device.

    In the 5 GHz band, you probably are using:
    1. 3 spatial streams (again, I couldn't find a spec sheet showing how many radio chains this router has, but 4x4 basically never exists, ever)
    2. A short guard interval
    3. An 80 MHz channel (5 GHz is big enough that we can get away with this... for now)

    This all adds up to a max data rate of 1300mbps. Let's do the math again: with a 3x3 device, you might hit 780mbps. With a 1x1 device, you might hit 260 mbps. Again, that's assuming that you lose 40 percent of bandwidth to management overhead, and that's still assuming that conditions are insanely perfect. You probably still won't see those values in the real world due to background noise, interference, and distance from the router.

    As for the AC68U, I found the specifications page for it, and it cites 600 mbps, which just isn't true. That would require 4x4 spatial streams, which I guarantee that device doesn't have (only one device ever supported it). I would say that it 's just a simple oversight by their marketing team, which in my opinion is not a big deal at all. This stuff is really heavy and really technical... simple mistakes like that are going to happen, and are of little consequence.

    Digging into the AC68U a bit more, I'll bet that to see a data rate of 216.7, you have 3x3 spatial streams, a 20 MHz channel, and a short guard interval. The only difference between the AC68U (216.7 mbps) and EA6500 (450 mbps) is most likely the configured channel width, 20 vs 40 MHz. You could go change them from 20 to 40, and back again to see if I'm right.

    I really hope that no one who REALLY knows what they are talking about reads this, because I could have this all wrong! My primary source for understanding how data rates work is by looking at the 802.11ac Survival Guide. Our engineers generally go directly to the 802.11 spec because they are... well, you know, engineers.
    Last edited by Joel; 02-01-2016 at 05:31 PM.
    Joel, Mobility+, ECSE, CWNE #233
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