Wireless Access

It is well known that 802.11ac produces high data rates, and most people assume that you can only take advantage of higher rates when you are running 40 or 80mhz channels.  Some people cannot run 40 or 80 mhz channels due to their high density requirements.   Enabling Very High Throughput (VHT) on your 802.11a radio profile even when running 20mhz channels will also increase performance for 802.11ac clients that are connecting to those same 20mhz channels:

Here is the output of two devices connecting to an access point running 20mhz channels with VHT turned off (802.11n or HT is turned on):  One is 3 spatial stream 802.11ac MacBook Pro and the other is a single spatial stream 802.11ac smartphone:

Note the  TX and RX rates of those two devices when VHT is turned off:

When VHT is enabled, there is no change in channel width, but we recognize clients that can take advantage of 802.11ac when VHT is enabled and we put VHT in the phy type column:

Both of those clients also receive a bump in their TX and RX rate when VHT is enabled:

The access point is only running 20 mhz channels, but just enabling VHT in the 802.11a radio profile will give a boost to 802.11ac capable clients connecting to an 802.11ac access point with VHT enabled.

(host) #show ap ht-rates bssid 00:1a:1e:1e:5a:10
 
AP "AL12" Radio 0 BSSID 00:1a:1e:1e:5a:10 High-throughput Rates (Mbps)
----------------------------------------------------------------------
MCS  Streams  20 MHz  40 MHz  40 MHz SGI
---  -------  ------  ------  ----------
  0   1          6.5    13.5    15.0
  1   1         13.0    27.0    30.0
  2   1         19.5    40.5    45.0
  3   1         26.0    54.0    60.0
  4   1         39.0    81.0    90.0
  5   1         52.0   108.0   120.0
  6   1         58.5   121.5   135.0
  7   1         65.0   135.0   150.0
  8   2         13.0    27.0    30.0
  9   2         26.0    54.0    60.0
 10   2         39.0    81.0    90.0
 11   2         52.0   108.0   120.0
 12   2         78.0   162.0   180.0
 13   2        104.0   216.0   240.0
 14   2        117.0   243.0   270.0
 15   2        130.0   270.0   300.0

(host) # show ap vht-rates bssid 6c:f3:7f:e6:52:f1
AP "Corp-ac" Radio 0 BSSID 6c:f3:7f:e7:51:f0 Very-high-throughput Rates (Mbps)
------------------------------------------------------------------------------
MCS  Streams  20 MHz  20 MHz SGI  40 MHz  40 MHz SGI  80 MHz   80 MHz SGI
---  -------  ------  ----------  ------  ----------  ------   ----------
0    1          6.5     7.2        13.5    15.0        29.3     32.5
1    1         13.0    14.4        27.0    30.0        58.5     65.0
2    1         19.5    21.7        40.5    45.0        87.8     97.5
3    1         26.0    28.9        54.0    60.0       117.0    130.0
4    1         39.0    43.3        81.0    90.0       175.5    195.0
5    1         52.0    57.8       108.0   120.0       234.0    260.0
6    1         58.5    65.0       121.5   135.0       263.3    292.5
7    1         65.0    72.2       135.0   150.0       292.5    325.0
8    1         78.0    86.7       162.0   180.0       351.0    390.0
9    1         --      --         180.0   200.0       390.0    433.3
0    2         13.0    14.4        27.0    30.0        58.5     65.0
1    2         26.0    28.9        54.0    60.0       117.0    130.0
2    2         39.0    43.3        81.0    90.0       175.5    195.0
3    2         52.0    57.8       108.0   120.0       234.0    260.0
4    2         78.0    86.7       162.0   180.0       351.0    390.0
5    2        104.0   115.6       216.0   240.0       468.0    520.0
6    2        117.0   130.0       243.0   270.0       526.5    585.0
7    2        130.0   144.4       270.0   300.0       585.0    650.0
8    2        156.0   173.3       324.0   360.0       702.0    780.0
9    2         --      --         360.0   400.0       780.0    866.7
0    3         19.5    21.7        40.5    45.0        87.8     97.5
1    3         39.0    43.3        81.0    90.0       175.5    195.0
2    3         58.5    65.0       121.5   135.0       263.3    292.5
3    3         78.0    86.7       162.0   180.0       351.0    390.0
4    3        117.0   130.0       243.0   270.0       526.5    585.0
5    3        156.0   173.3       324.0   360.0       702.0    780.0
6    3        175.5   195.0       364.5   405.0        --       --
7    3        195.0   216.7       405.0   450.0       877.5    975.0
8    3        234.0   260.0       486.0   540.0       1053.0   1170.0
9    3        260.0   288.9       540.0   600.0       1170.0   1300.0

Thanks for the great tutorial!  I assume the bump comes from improved modulation?

---

@thecompnerd wrote:

Thanks for the great tutorial!  I assume the bump comes from improved modulation?

---

Yes, it does.

>> Thanks for the great tutorial! I assume the bump comes from improved modulation?

>Yes, it does.

What is actually enabled underneath with the "Enable VHT" setting on the Aruba controller?  

Which modulation are you referring to that's improved in the context of VHT?  There's the VHT-sigA and VHT-sigB fields, and VHT-sigB uses slightly improved modulation over VHT-sigA (both BPSK but the whole VHT-sigB field can fit into a single OFDM symbol, whereas VHT-sigA's modulation is limited to 24 bits per symbol) -- whew -- is that what you're referring to?  Please bark me up the right tree if this is the wrong one :).

Also, do you know what "sgi" means in "a-VHT-40sgi-2ss" (the "phy" column in 'show ap association' ) ?   I also see output like "g-HT-20sgi-2ss" so it's not just 802.11ac clients.   The 6.3.x CLI guide for that command skips that column, and there's no flag description for it in the command output.

tx,

and rx,

-nb.

http://www.arubanetworks.com/techdocs/ArubaOS_64_Web_Help/Web_Help_Index.htm#ArubaFrameStyles/1CommandList/show_ap_vht-rates.htm?Highlight=vht

(6.4.x reference also skips the "phy" column output description, not to be confused with the "phy" argument to the command.)

Anyway, "sgi" means "short guard interval."

-nb

Great Stuffs. Thanks Joseph.

Thanks, but might wanna leave the screenshots a tiny bit bigger next time please.

What screenshots?

the last 3 command outputs.

Can you see what they say?

Barely. I did zoom in to stop myself from squinting to see it properly.

May just be me, I do not have the best eyesight in the world.

Just kidding :)

Unfortunately the command that shows the association rate has alot of columns and it is very very small as a result.  I could just post the result and hope that everyone just believes me...  Hopefully everyone understands what they need to do to replicate this and they don't have to squint at my data..

Heheh, pease don't. Better this way.

I just figured bigger pictures would just extend past to border of the forum into the huge grey wastes next to it if needed. 

Thank you Colin!  Great doc on enabled VHT in 20mhz. 

Question, I thinking to disable even the 40Mhz and remove dfs.  Due to some legacy devices issue. 

I have

"ARM" allow bands for 40MHz channel to be none, and 80MHz support unchecked

"802.11a radio profile" checked on both High Throughtput enable radio, very high thoughtput enable (radio) channel width 20MHz.

However I still see "a-HT-40sgi-1ss" in "show ap associateion"

Thanks,

=SL=

That might be a bug.  You might want to open a TAC case...

Hi!

Thanks for quite reply!  Actually I over look the show ap association output .  Looking at the AP that does not have vht 40 and 80 disabled.  However, I took you advice and disable 40 and 80 in High-Thoughput SSID Profile and check on both Hight throughput and Very high throughput enable.

Thanks!

=SL=