how to troubleshoot 802.11n speeds

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Updated: Aug 18, 2010Document ID: 112055

Troubleshoot 802.11n Speeds

on en s

IntroductionPrerequisites

RequirementsComponents UsedConventions

Background InformationTroubleshoot the Controller for 11n Speeds

How to Calculate Throughput via iPerf Capabilities Advertised in Beacons

Related Information

Introducti onhis document covers comm on issues to consider when

roubleshooting wireless throug hput issues. This documentincludes usage of tools to measure performance andhroughput of the wireless network, which includes differentendor 8 02.11n access points (APs) in comparison with the

Cisco 1252 AP under similar test conditions.

Prerequisites

Requirements

Cisco recommends that you have these requirements:

ools such as iPerf, and network analyzers such asOmniPeek and Cisco Spectrum Analysis

802.11n supported 1140, 1250, 3500, and 1260 Series APs

Components Used

he information in this document is based on these softwareand hardware versions:

S-SVC-WiSM Controller running software version 6.0.182

AIR-LAP1142-A-K9 APs

Conventions

Refer to Cisco Technical Tips Conventions for moreinformation on document conventions.

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Background Information802.11n is born due to a number of changes made on the APsFrame Aggregation: A-MPDU and A-MSDU.

Block Ack Size

MCS and Channel Bonding

MIMO

Using 5GHz over 2.4 GHz: also mention Wi-Fi certifieschannel bonding on 5GHz

Troubleshoot the Controller for 11nSpeedsComplete these steps:

Verify that 802.11n support is enabled on the controller.

N rates are attained two ways. Speeds up to ModulationCoding scheme (MCS) 7 can be attained without usingchannel 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 onhe controller:

(WiSM-slot3-2) >show 802.11a802.11a Network..................................

11nSupport.......................................802.11a Low Band........................... Enable802.11a Mid Band........................... Enable802.11a High Band.......................... Enable802.11a Operational Rates802.11a 6M Rate.............................. Man802.11a 9M Rate.............................. Supp802.11a 12M Rate............................. Dis802.11a 18M Rate............................. Supp802.11a 24M Rate............................. Man802.11a 36M Rate............................. Supp802.11a 48M Rate............................. Supp802.11a 54M Rate............................. Supp

802.11n MCS Settings:MCS 0........................................ SuppMCS 1........................................ SuppMCS 2........................................ SuppMCS 3........................................ SuppMCS 4........................................ SuppMCS 5........................................ Supp

(WiSM-slot3-2) >show advanced 802.11a channelAutomatic Channel AssignmentChannel Assignment Mode........................ AChannel Update Interval........................ 60Anchor time (Hour of the day).................. 0Channel Update Contribution.................... SChannel Assignment Leader...................... 00Last Run....................................... 37DCA Sensitivity Level.......................... SDCA 802.11n Channel Width...................... 40Channel Energy LevelsMinimum...................................... unkAverage...................................... unkMaximum...................................... unkChannel Dwell TimesMinimum...................................... unk


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

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

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

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

On the WLAN configured for client connectivity, WMMshould be allowed or required, and AES or open encryptiononly must be used. This can be verified using this commandoutput:

CFP Period.......................................CFP Maximum Duration.............................Default Channel..................................Default Tx Power Level...........................DTPC Status..................................... EFragmentation Threshold..........................Pico-Cell Status.................................Pico-Cell-V2 Status..............................TI Threshold.....................................Traffic Stream Metrics Status....................

Expedited BW Request Status......................World Mode.......................................EDCA profile type................................Voice MAC optimization status....................Call Admission Control (CAC) configurationVoice AC - Admission control (ACM)............ EnVoice max RF bandwidth........................ 75Voice reserved roaming bandwidth.............. 6Voice load-based CAC mode..................... EnVoice tspec inactivity timeout................ DisVideo AC - Admission control (ACM)............ DisVoice Stream-Size............................. 840Voice Max-Streams............................. 2Video max RF bandwidth........................ InfVideo reserved roaming bandwidth.............. 0

(WiSM-slot2-2) >show wlan 1WLAN Identifier..................................Profile Name.....................................Network Name (SSID)..............................Status...........................................

MAC Filtering....................................Broadcast SSID...................................AAA Policy Override..............................Network Admission ControlNAC-State...................................... DiQuarantine VLAN................................ 0Number of Active Clients.........................Exclusionlist Timeout............................Session Timeout..................................CHD per WLAN.....................................Webauth DHCP exclusion...........................Interface........................................WLAN ACL.........................................

DHCP Server......................................DHCP Address Assignment Required.................Quality of Service............................... MM..............................................CCX - AironetIe Support..........................CCX - Gratuitous ProbeResponse (GPR).............CCX - Diagnostics Channel Capability.............


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Antenna Diversity: if using only two antennas for anyreason, you need to use antenna A and B for ransmitter/receiver ports.

On the Client side:

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

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

Contact your wireless adapter vendor.

Make sure you are using 11n certified adapter to achieve11n data rates.

i-Fi certified products:

http://www.wi-fi.org/certified_products.php

Dot11-Phone Mode (7920)..........................Wired Protocol...................................IPv6 Support.....................................Peer-to-Peer Blocking Action.....................Radio Policy.....................................DTIM period for 802.11a radio....................DTIM period for 802.11b radio....................Radius ServersAuthentication................................ GloAccounting.................................... Dis

Local EAP Authentication.........................Security802.11 Authentication:........................ OpeStatic WEP Keys............................... Dis802.1X........................................ DisWi-Fi Protected Access (WPA/WPA2)............. EnWPA (SSN IE)............................... DisablWPA2 (RSN IE).............................. EnableTKIP Cipher............................. Disabled

ES Cipher.............................. Enabled Auth Key Management802.1x.................................. EnabledPSK..................................... DisabledCCKM.................................... DisabledFT(802.11r)............................. DisabledFT-PSK(802.11r)......................... DisabledFT Reassociation Timeout.........................FT Over-The-Air mode.............................FT Over-The-Ds mode..............................CKIP ......................................... DisIP Security................................... DisIP Security Passthru.......................... DisWeb Based Authentication...................... DisWeb-Passthrough............................... DisConditional Web Redirect...................... DisSplash-Page Web Redirect...................... DisAuto Anchor................................... DisH-REAP Local Switching........................ EnH-REAP Learn IP Address....................... EnInfrastructure MFP protection................. EnInfrastructureMFP Disabled)Client MFP.................................... OptTkip MIC Countermeasure Hold-down Timer....... 60Call Snooping....................................Band Select......................................Load Balancing...................................

http://www.wi-fi.org/certified_products.php


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How to Improve Performance:

Channel utilization—Network analyzers report channelutilization in percentage of time spent transmitting andreceiving frames. This helps to measure the potential

ariance in speed due to distance from an access point.his will help monitor and see for example, if a channel is

ully occupied transmitting at 1Mbps under ideal conditionsould perform at 0.94Mbps under 100% utilization.

he physical medium used in wireless as well dictates theperformances. Using 802.11g or 802.11a over 802.11boffers much higher throughputs, often up to 30 mbps over 802.11b where a 6mpbs radio capacity is divided betweenall the associated stations.

Cell Sizes—It is recommended to shrink the cell sizes tohave the clients as closer to the APs as possible. This willbenefit 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.

Shrinking cell size also decreases co-channel interference.If using RRM, the APs should pick channels dynamically per he deployment. However, if implementing dynamic channel

assignment, ensure that you do not have two APs at highpower levels on the same channel right next to each other.

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 athttp://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

http://www.macalester.edu/crash/software/pc/iperf/kperf_setup.exe


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his is an example of Omnipeek captures to analyzeggregate MAC protocol data unit :

-MPDU Setup

ADDBA—Add Block Acknowledgement

ADDBA Request—Contains identifier, Block Ack Policy,Buffer Size, etc.

ADDBA Response—Can change policy and buffer size.

-MPDU Setup

ADDBA Request

AP1250 uses a timeout of zero to indicate no timeout.

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-MPDU Setup

ADDBA Response

Receiver needs to indicate Block Ack Agreement was

successfully established.



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-MPDU Data Transfer

Block Ack contains compressed bitmap to indicate MPDUsreceived.

Refer to the IEEE 802.11n section 9.10.7 “HT-immediateBlock Ack extensions” for information on sending the Block

Ack.

Capabilities Advertised in Beacons

Capabilities advertised in Beacons:



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Capabilities advertised in Beacons:

ssociation similar with addition of Block Ack setup for A-MPDU:



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