Wireless and RF

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don
Contributor I

802.11N Throughput testing

This morning we did some testing with a high-throughput wlan (see profile at the bottom of the page) using the Aruba 125. We setup the VennLab HT SSID for testing locally using 802.11n on the 5Ghz channels exclusively. We also enabled the 40Mhz wide channel in order to maximize throughput. Our testing yielded very good results as you can see below.
Our test setup consists of two MacBook Pro’s each running the iperf network utility (via MacPorts) with manually configured IP addresses. To establish a baseline, we first connected to RLAB, a network that is already established on our Aruba infrastructure. This is an 802.11g only isolated wlan that also allows client to client connectivity.
Connected to "RLAB" to get a baseline, the airport sees an RSSI of –49 which is typical of a very good connection and shows a transmit rate of 54 as would be expected. Here are the iperf stats using the default settings:

Macintosh-214:~ donwright$ iperf -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 256 KByte (default)
------------------------------------------------------------
Tested first with RLAB (802.11g standard wlan)

local 10.10.10.4 port 5001 connected with 10.10.10.3 port 49335
Interval Transfer Bandwidth
0.0-10.1 sec 8.45 MBytes 7.04 Mbits/sec

This seems low, but maybe that’s an iperf thing, which is kind of confusing since they use the capital M for megabits. If I take this at face value and move on, the increase with 802.11n does show up.

Connecting to my 802.11n "VennLab" shows a similar RSSI of 50, but with a Transmit Rate of 300, a 6X increase. This increase seems to be validated in the iperf tests below which average about a 6X jump to 50 Mbits/sec.

local 10.10.10.4 port 5001 connected with 10.10.10.3 port 49336
Interval Transfer Bandwidth
0.0-10.0 sec 57.5 MBytes 48.2 Mbits/sec
local 10.10.10.4 port 5001 connected with 10.10.10.3 port 49337
Interval Transfer Bandwidth
0.0-10.0 sec 56.1 MBytes 47.0 Mbits/sec
local 10.10.10.4 port 5001 connected with 10.10.10.3 port 49338
Interval Transfer Bandwidth
0.0-10.0 sec 64.4 MBytes 53.9 Mbits/sec
local 10.10.10.4 port 5001 connected with 10.10.10.3 port 49339
Interval Transfer Bandwidth


What is not clear is the use of the 40Mhz channel. We have verified that the AP is configured correctly, but the client is reporting using the single channel 153 instead of something like (153,157). This may be just how the Mac reports the wireless configuration, I'm not sure.

My questions are:

Do I have this tweaked to the max for 802.11n performance ?

Is there something better than iperf that I should use for throughput testing ?

Does the Macbook Pro (OSX 10.5.6, Atheros nics) really take advantage of the 40Mhz channel and how can I tell if I’m running in 2x2 ?
Aruba Employee

Macintosh wireless info



Does the Macbook Pro (OSX 10.5.6, Atheros nics) really take advantage of the 40Mhz channel and how can I tell if I’m running in 2x2 ?




You can get better info about what your Mac's wireless card is doing using the airport command line utility. It is hidden in /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport

It will give you output like this:

$ airport --getinfo
agrCtlRSSI: -43
agrExtRSSI: -64
agrCtlNoise: -92
agrExtNoise: -92
state: running
op mode: station
lastTxRate: 300
maxRate: 270
lastAssocStatus: 0
802.11 auth: open
link auth: wpa2
BSSID: 0:1a:1e:6f:89:10
SSID: alpha
MCS: 15
channel: 48,-1

The last shows you that this Mac (a Macbook Pro using the atheros 5008 and 10.5.6) is using the bonded pair 48,44. Otherwise known as 48-.
Note, I do not have documentation on this tool. I compared these results to a packet capture and confirmed the Mac was receiving 40Mhz data frames.

Best,
-Jeremy
don
Contributor I

Re: 802.11N Throughput testing

Thanks Jeremy, I checked the Mac again and using the airport -I shows channels 149 and 153 in use.

Macintosh-214:~ donwright$ airport -I
agrCtlRSSI: -53
agrExtRSSI: -84
agrCtlNoise: -100
agrExtNoise: -100
state: running
op mode: station
lastTxRate: 243
maxRate: 270
lastAssocStatus: 0
802.11 auth: open
link auth: unknown
BSSID: 0:1a:1e:8a:70:70
SSID: VennLab
MCS: 14
channel: 149,1