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This article provides an overview of the basic elements for a healthy WiFi environment, including signal strength, RF noise floor, clean RF channels, and client WiFi NIC driver and firmware. It also highlights central and standalone tools for troubleshooting WiFi issues.
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WiFiRF TroubleshootingGeneral Overview Westnet 2015 Marcelo Lew January 15th, 2015
Basic Elements for a Healthy WiFi Environment 1. Signal Strength and Signal to Noise Ratio • Clients should get a 25db SNR or above for 3+ bars graphical representation on device. • RF Scanner Signal RSSI of -65dbm or above • A minimum of 25-30 SNR is CRUCIAL to decode high 802.11n and ac data rates.
Basic Elements for a Healthy WiFi Environment 2. Low RF Noise Floor • RF Scanner Noise RSSI of -90dbm or below
Basic Elements for a Healthy WiFi Environment 3. Clean RF Channels • No or few Adjacent (overlapping) Channel Interference: When networks are active on overlapping channels performance is reduced as networks compete to get air time to send frames. Overlapping channel interference would be perceived as noise from the client perspective yielding high re-transmit levels.
Basic Elements for a Healthy WiFi Environment 3. Clean RF Channels (continue) • Non-WiFiInterference: Other sources of interference could be running on the same channel or band (i.e. Microwave oven, Bluetooth devices) • Co-Channel Interference: When networks are active on the same channel performance is also reduced as beacons and probe responses are transmitted to each client device that is looking for a WiFi connection creating a lot of management overhead on the network. The issue becomes worst if access points are transmitting these frames at default rates (1 and 2mbps, which most home wifi routers are).
Basic Elements for a Healthy WiFi Environment 4. Client WiFi NIC Driver and Firmware: An outdated driver can cause several issues that affect the RF Environment (i.e. choosing the best RF band, roaming delays, authentication issues creating bottlenecks, etc.).
Central tools to troubleshoot WiFi Issues 1. Controller and/or Management server dashboard: Most of today’s WiFi networks have a central management console where to look at a client from the network (WAP) perspective. This is a good start to look at SNR, Noise, Channel Utilization, Interference, etc. You can also setup triggers to alert you based on channel utilization, low snr, etc. • Next slide shows some examples from Aruba/Airwave Dashboard for AP and Client troubleshooting:
Stand alone tools to troubleshoot specific WiFi issues 1. Once you identified there is indeed an RF network side issue, one of my favorite tools is “Eye P.A. with AirPcap capture card” from MetaGeek. This software will allow you to capture all three types of 802.11 frames (Data, Management, and Control). Management and Control frames will never make it to the Ethernet side since they are only 802.11 overhead frames, therefore sniffers on the wired will not see this traffic. By looking at an Eye PA Capture you can quickly identified the areas that are causing the issue. Once you have the capture, you can upload it to your favorite packet capture software to analyze it if you prefer. Next slide are Eye P.A. screenshots from a 40 seconds capture during a conference, including the Visualize Tab, Analyze Tab, and Packets Tab:
Stand alone tools to troubleshoot specific WiFi issues 2. Another good tool from MetaGeek is “insider”, a basic WiFi network analyzer to quickly identify areas that need further troubleshooting. The new version integrates very nicely with Eye P.A. 3. An RF Spectrum Analyzer can also be helpful to determine sources of interference from non-WiFi devices. The new “software based” spectrum analyzers are very good and have a short learning curve versus dedicated spectrum analyzers. Airmagnet Spectrum XT and MetaGeek Wi-Spy/Chanalyzerare both very good products in my opinion.
