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.
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
The information in this document is based on these software and hardware versions:
WS-SVC-WiSM Controller running software version 6.0.182
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
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.
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
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