Can't find what you need?


• Ask the Community
• Create a Case
Reset Search
 

 

Article

How do I measure the wireless performance of a client on an access point and what factors might impact performance

« Go Back

Information

 
TitleHow do I measure the wireless performance of a client on an access point and what factors might impact performance
Objective
How do I measure the wireless performance of a client on an access point and what factors might impact performance?
Environment
  • IdentiFi wireless
  • Client performance
Procedure
When testing wireless performance in the real world there are many factors that can influence performance.

1) Link (PHY) Speed
 
PHY speed is the data rate the client is able to communicate, this speed is dependent on the SNR received by the client, the worse the SNR, the slower the data rate will be.  PHY speed also depends on the AP capability and the client capability.  You can find out client capabilities by knowing the number of rx/tx radio chains and spatial streams (eg 2x2:2) and looking at this table: http://mcsindex.com/  In Windows task manager will show the PHY speed in real time.  As an approximate guide, for a single client on a clean channel you can expect a data transfer rate of around half the PHY speed.

2) Radio configuration

Configuration of the radio will vary from site to site and possibly even building to building within a site.  Wholesale radio changes should be done with care, however as a general guideline the following settings would give a working baseline.

Outside of the radio configuration, WLAN service: ensure WMM is enabled, this is a requirement for HT/VHT devices to achieve higher data rates.  Encryption, if used, should be WPA/v2 for the same reason (WPA/v1 or WEP cannot operate at higher data rates.)

2.4Ghz radio:
  • 20Mhz channel width
  • Eliminate legacy data rates (802.11b) by setting radio mode to g/n
5Ghz radio:
  • 40Mhz channel width, 80Mhz can be used but care must be taken to chose a clear channel, typically in the real world 40Mhz width gives more channels and more capacity.
  • Ensure tx power is enough to provide an SNR that allows highest data rates possible.
Both radios:
  • Short guard interval (400ns)
  • DTIM of 1 or 2 (default is 5)
  • Protection auto
  • Aggregate MSDU disabled
  • Aggregate MPDU enabled
  • ADDBA support enabled
  • ATPC off
3) Background traffic, especially broadcast and multicast types
 
Due to the fact that 802.11 wireless is half duplex and a shared medium any additional traffic on the access point, including on other SSID's will impact on performance.    It is recommend to test on a single ssid with a single vlan and on a channel that is as clean as possible.

4) RF interference, ACI/CCI

What is Co and Adjacent Channel Interference

Other AP's or clients operating on the same channel will add to contention and thus reduce performance. You may also see a lot of re-transmissions if not all devices can hear each other.

5) Ethernet link speed
 
An AP operating with only a 100Mbps ethernet link will have a bottleneck when serving HT/VHT clients on 802.11n or 802.11ac, check ethernet port configuration 

6) Client configuration
  • Use the latest manufacturers drivers
  • Connect the device to mains power where possible (for example a laptop should not be on battery)
  • Disable power save if possible (typically on Windows devices.)
7) Testing tools
  • Frequently web based tools such as speedtest.net are used, these tools are good to give an indication of performance but they add in some unknowns caused by the vagaries of the internet.
  • iperf is a useful tool and is best done with a wired client and a wireless client.  Iperf has 2 modes, server and client, the server is a receiver and the client is a sender, measurements can be taken in both directions by alternating the wireless and wired client between iperf server/client mode.  An example iperf command that sets up 6 parallel TCP streams with a TCP window size of 256k and abbreviated example results could be:
 
Iperf -c <server IP address> -P 6 -w 256k -r -t 60

- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-60.01  sec   200 MBytes  28.0 Mbits/sec                  sender
[  4]   0.00-60.01  sec   200 MBytes  28.0 Mbits/sec                  receiver
[  6]   0.00-60.01  sec   206 MBytes  28.8 Mbits/sec                  sender
[  6]   0.00-60.01  sec   206 MBytes  28.8 Mbits/sec                  receiver
[  8]   0.00-60.01  sec   205 MBytes  28.6 Mbits/sec                  sender
[  8]   0.00-60.01  sec   205 MBytes  28.6 Mbits/sec                  receiver
[ 10]   0.00-60.01  sec   204 MBytes  28.6 Mbits/sec                  sender
[ 10]   0.00-60.01  sec   204 MBytes  28.6 Mbits/sec                  receiver
[ 12]   0.00-60.01  sec   199 MBytes  27.8 Mbits/sec                  sender
[ 12]   0.00-60.01  sec   199 MBytes  27.8 Mbits/sec                  receiver
[ 14]   0.00-60.01  sec   203 MBytes  28.4 Mbits/sec                  sender
[ 14]   0.00-60.01  sec   203 MBytes  28.4 Mbits/sec                  receiver
[SUM]   0.00-60.01  sec  1.19 GBytes   170 Mbits/sec                  sender
[SUM]   0.00-60.01  sec  1.19 GBytes   170 Mbits/sec                  receiver





 
Additional notes

Feedback

 

Was this article helpful?


   

Feedback

Please tell us how we can make this article more useful.

Characters Remaining: 255