Troubleshooting 802.11n Speeds

vbaliwad · ‎01-06-2011

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

Leo Laohoo · ‎01-06-2011

Nice one. Keep `em coming!