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Troubleshooting 802.11n Speeds

Troubleshoot 802.11n Speeds

Contents:

  • Introduction
  • Prerequisites     
  • Requirements      
  • Components Used      
  • Conventions Background Information Troubleshoot the Controller for 11n Speeds     
  • How to Calculate Throughput via iPerf      
  • Capabilities Advertised in Beacons

This document covers common issues to consider when troubleshooting wireless throughput issues. This document includes usage of tools to measure performance and throughput of the wireless network, which includes different vendor 802.11n access points (APs) in comparison with the Cisco 1252 AP under similar test conditions.

Prerequisites Requirements

Cisco recommends that you have these requirements:

  •   Tools such as iPerf, and network analyzers such as OmniPeek and Cisco Spectrum Analysis   
  •    802.11n supported 1140, 1250, 3500, and 1260 Series APs 


Components Used

The information in this document is based on these software and hardware versions:   

  WS-SVC-WiSM Controller running software version 6.0.182  

  AIR-LAP1142-A-K9 APs

Background Information  802.11n is born due to a number of changes made on the APs Frame Aggregation: A-MPDU and A-MSDU.  

  • Block Ack Size   
  • MCS and Channel Bonding   
  • MIMO  
  • Using 5GHz over 2.4 GHz: also mention Wi-Fi certifies channel bonding on 5GHz 

Troubleshoot the Controller for 11n Speeds  Complete these steps:  

1.        Verify that 802.11n support is enabled on the controller.         

(WiSM-slot3-2) >show 802.11a        

802.11a Network.................................. Enabled        

11nSupport....................................... Enabled        

802.11a Low Band........................... Enabled        

802.11a Mid Band........................... Enabled        

802.11a High Band.......................... Enabled

802.11a Operational Rates        

802.11a 6M Rate.............................. Mandatory        

802.11a 9M Rate.............................. Supported        

802.11a 12M Rate............................. Disabled        

802.11a 18M Rate............................. Supported        

802.11a 24M Rate............................. Mandatory        

802.11a 36M Rate............................. Supported        

802.11a 48M Rate............................. Supported        

802.11a 54M Rate............................. Supported

802.11n MCS Settings:        

MCS 0........................................ Supported        

MCS 1........................................ Supported        

MCS 2........................................ Supported        

MCS 3........................................ Supported        

MCS 4........................................ Supported        

MCS 5........................................ Supported  

2.  N rates are attained two ways. Speeds up to Modulation Coding scheme (MCS) 7 can be attained without using channel bonding. For MCS rates above 7 and up to 15, channel bonding needs to be enabled. You can verify if channel bonding is enabled using this show command on the controller:        

(WiSM-slot3-2) >show advanced 802.11a channel        

Automatic Channel Assignment        

Channel Assignment Mode........................ AUTO        

Channel Update Interval........................ 600 seconds [startup]        

Anchor time (Hour of the day).................. 0        

Channel Update Contribution.................... SNI.        

Channel Assignment Leader...................... 00:1d:45:f0:d2:c0        

Last Run....................................... 371 seconds ago        

DCA Sensitivity Level.......................... STARTUP (5 dB)        

DCA 802.11n Channel Width...................... 40 MHz        

Channel Energy Levels           Minimum...................................... unknown        

Average...................................... unknown        

Maximum...................................... unknown        

Channel Dwell Times           Minimum...................................... unknown        

Average...................................... unknown        

Maximum...................................... unknown        

802.11a 5 GHz Auto-RF Channel List        

Allowed Channel List.........................           36,40,44,48,52,56,60,64,149,153,157,161        

Unused Channel List..........................           100,104,108,112,116,132,136,  

3. You can also configure channel width per AP using these commands:         

(WiSM-slot2-2) >config 802.11a disable AP0022.9090.8e97        

(WiSM-slot2-2) >config 802.11a chan_width AP0022.9090.8e97 40        

Set 802.11a channel width to 40 on AP AP0022.9090.8e97  

4.  The Guard interval and corresponding MCS rates help determine the data rates that are seen on the 802.11n clients. These are the commands to verify this configuration:         

(WiSM-slot3-2) >show 802.11a        

802.11a Network.................................. Enabled        

11nSupport....................................... Enabled        

802.11a Low Band........................... Enabled        

802.11a Mid Band........................... Enabled        

802.11a High Band.......................... Enabled        

802.11a Operational Rates        

802.11a 6M Rate.............................. Mandatory        

802.11a 9M Rate.............................. Supported        

802.11a 12M Rate............................. Disabled        

802.11a 18M Rate............................. Supported        

802.11a 24M Rate............................. Mandatory        

802.11a 36M Rate............................. Supported        

802.11a 48M Rate............................. Supported        

802.11a 54M Rate............................. Supported        

802.11n MCS Settings:        

MCS 0........................................ Supported        

MCS 1........................................ Supported        

MCS 2........................................ Supported        

MCS 3........................................ Supported        

MCS 4........................................ Supported        

MCS 5........................................ Supported        

MCS 6........................................ Supported        

MCS 7........................................ Supported        

MCS 8........................................ Supported        

MCS 9........................................ Supported        

MCS 10....................................... Supported        

MCS 11....................................... Supported        

MCS 12....................................... Supported        

MCS 13....................................... Supported        

MCS 14....................................... Supported        

MCS 15....................................... Supported        

802.11n Status:           A-MPDU Tx:        

Priority 0............................... Enabled        

Priority 1............................... Disabled        

Priority 2............................... Disabled        

Priority 3............................... Disabled        

Priority 4............................... Disabled        

Priority 5............................... Disabled        

Priority 6............................... Disabled        

Priority 7............................... Disabled        

Beacon Interval.................................. 100        

CF Pollable mandatory............................ Disabled        

CF Poll Request mandatory........................ Disabled        

CFP Period....................................... 4        

CFP Maximum Duration............................. 60        

Default Channel.................................. 36        

Default Tx Power Level........................... 1        

DTPC Status..................................... Enabled          

Fragmentation Threshold.......................... 2346          

Pico-Cell Status................................. Disabled          

Pico-Cell-V2 Status.............................. Disabled         

TI Threshold..................................... -50          

Traffic Stream Metrics Status.................... Disabled          

Expedited BW Request Status...................... Disabled         

World Mode....................................... Enabled          

EDCA profile type................................ default-wmm          

Voice MAC optimization status.................... Disabled          

Call Admission Control (CAC) configuration          

Voice AC - Admission control (ACM)............ Enabled          

Voice max RF bandwidth........................ 75          

Voice reserved roaming bandwidth.............. 6         

Voice load-based CAC mode..................... Enabled          

Voice tspec inactivity timeout................ Disabled          

Video AC - Admission control (ACM)............ Disabled         

Voice Stream-Size............................. 84000          

Voice Max-Streams............................. 2          

Video max RF bandwidth........................ Infinite          

Video reserved roaming bandwidth.............. 0      

Ensure A-MPDU packet aggregation. For best effort, QoS levels are enabled via these commands:         

              config 802.11a 11nSupport a-mpdu tx priority 0 enable       

             config 802.11b 11nSupport a-mpdu tx priority 0 enable 

5.   All three antennas on the A radio must be used. Make sure the antennas are the same model.  

6.   On the WLAN configured for client connectivity, WMM should be allowed or required, and AES or open encryption only must be used. This can be verified using this command output:          

(WiSM-slot2-2) >show wlan 1          

WLAN Identifier.................................. 1         

Profile Name..................................... wlab5WISMip22          

Network Name (SSID).............................. wlab5WISMip22          

Status........................................... Enabled          

MAC Filtering.................................... Disabled         

Broadcast SSID................................... Enabled          

AAA Policy Override.............................. Disabled          

Network Admission Control           NAC-State...................................... Disabled         

Quarantine VLAN................................ 0          

Number of Active Clients......................... 0          

Exclusionlist Timeout............................ 60 seconds         

Session Timeout.................................. 1800 seconds          

CHD per WLAN..................................... Enabled          

Webauth DHCP exclusion........................... Disabled         

Interface........................................ management          

WLAN ACL......................................... unconfigured          

DHCP Server...................................... Default          

DHCP Address Assignment Required................. Disabled          

Quality of Service............................... Silver (best effort)          

WMM.............................................. Allowed          

CCX - AironetIe Support.......................... Enabled         

CCX - Gratuitous ProbeResponse (GPR)............. Disabled         

CCX - Diagnostics Channel Capability............. Disabled         

Dot11-Phone Mode (7920).......................... Disabled          

Wired Protocol................................... None         

IPv6 Support..................................... Disabled          

Peer-to-Peer Blocking Action..................... Disabled         

Radio Policy..................................... All          

DTIM period for 802.11a radio.................... 1          

DTIM period for 802.11b radio.................... 1         

Radius Servers         

Authentication................................ Global Servers          

Accounting.................................... Disabled         

Local EAP Authentication......................... Disabled          

Security         

802.11 Authentication:........................ Open System          

Static WEP Keys............................... Disabled          

802.1X........................................ Disabled          

Wi-Fi Protected Access (WPA/WPA2)............. Enabled          

WPA (SSN IE)............................... Disabled         

WPA2 (RSN IE).............................. Enabled         

TKIP Cipher............................. Disabled          

AES Cipher.............................. Enabled          

Auth Key Management           802.1x.................................. Enabled          

PSK..................................... Disabled          

CCKM.................................... Disabled          

FT(802.11r)............................. Disabled          

FT-PSK(802.11r)......................... Disabled          

FT Reassociation Timeout......................... 20          

FT Over-The-Air mode............................. Enabled          

FT Over-The-Ds mode.............................. Enabled         

CKIP ......................................... Disabled         

IP Security................................... Disabled         

IP Security Passthru.......................... Disabled          

Web Based Authentication...................... Disabled         

Web-Passthrough............................... Disabled         

Conditional Web Redirect...................... Disabled          

Splash-Page Web Redirect...................... Disabled         

Auto Anchor................................... Disabled          

H-REAP Local Switching........................ Enabled          

H-REAP Learn IP Address....................... Enabled         

Infrastructure MFP protection................. Enabled (Global         

Infrastructure           MFP Disabled)          

Client MFP.................................... Optional          

Tkip MIC Countermeasure Hold-down Timer....... 60          

Call Snooping.................................... Disabled          

Band Select...................................... Enabled         

Load Balancing................................... Enabled   

7. Antenna Diversity: if using only two antennas for any reason, you need to use antenna A and B for transmitter/receiver ports. 

On the Client side:    

1. Supplicant used to control the wireless card, preferred to match the vendor of the supplicant to the wireless card.   

2. Client drivers: you need to make sure the latest client drivers are running on the wireless cards.   

3. Contact your wireless adapter vendor.   

4. Make sure you are using 11n certified adapter to achieve 11n data rates.  Wi-Fi certified products:  http://www.wi-fi.org/certified_products.php 

Test Bed for 11n throughput:  http://www.cisco.com/en/US/prod/wireless/ideas_in_motion.html 

How to Improve Performance:   

1.Channel utilization—Network analyzers report channel utilization in percentage of time spent transmitting and receiving frames. This helps to measure the potential variance in speed due to distance from an access point. This will help monitor and see for example, if a channel is fully occupied transmitting at 1Mbps under ideal conditions would perform at 0.94Mbps under 100% utilization.   

2.The physical medium used in wireless as well dictates the performances. Using 802.11g or 802.11a over 802.11b offers much higher throughputs, often up to 30 mbps over 802.11b where a 6mpbs radio capacity is divided between all the associated stations.   

3.Cell Sizes—It is recommended to shrink the cell sizes to have the clients as closer to the APs as possible. This will benefit the data rates at which the client can connect to the AP. This can be done by reducing the power levels on the AP to the lowest.   

4.Shrinking cell size also decreases co-channel interference. If using RRM, the APs should pick channels dynamically per the deployment. However, if implementing dynamic channel assignment, ensure that you do not have two APs at high power levels on the same channel right next to each other.    5. Protection also causes throughput hit.  How to Calculate Throughput via iPerf Iperf Setup Tips  For those customers or testers that do not own Chariot, Iperf can be used instead. This is available at http://www.macalester.edu/crash/software/pc/iperf/kperf_setup.exe.

Measuring TCP Throughput  Run this command on the server side:     Iperf –s -w 256k

Run this command on the client side:      Iperf –c  -P 6 –w 256k -r –t 60 

The first circled number in this image represents the upstream throughput, the second circled number represents downstream (AP to client) throughput. Measuring UDP Throughput  Close the previous Iperf applications on both the server and client side. Both need to be set up again, but this time for UDP performance testing.

Run this command on the server side: Iperf –s -u –l 56k

Run this command on the client side:  Iperf –c -u –b 50M –l 56k –P 

Comments
Hall of Fame Super Gold

Nice one.  Keep `em coming!

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