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WiFi Metrics

I am going to pen down a few of the important wireless metrics. This is to access the environment for any concerns and issues raised around the wireless side of things.

So what should we consider a good, acceptable, or poor Wi-Fi signal strength?

-30 dBm – Maximum signal strength, you are probably standing right next to the access point.
-50 dBm – Anything down to this level can be considered excellent signal strength.
-60 dBm – Good, reliable signal strength.
67 dBm – Reliable signal strength.The minimum for any service depending on a reliable connection and signal strength, such as voice over Wi-Fi and non-HD video streaming.
-70 dBm – Not a strong signal. Light browsing and email.
-80 dBm – Unreliable signal strength, will not suffice for most services.Connecting to the network.
-90 dBm – The chances of even connecting are very low at this level.

RSSI – each device will have different values and output. There’s no defined way to track the RSSI. Client devices take lot of decisions based upon the RSSI. Wifi bars = one of the ways to determine RSSI. It is not always a good factor though as mac OS X tends to show full bars even though only 1 bar or dBm value around -80. Good numbers around RSSI is -67 for voice, typical connections -70. Location analytics tend to be around -60. Values in dBm. Mention website of RSSI.

Image Courtesy : eyesaas

SNR – quality of wireless signal. Level of noise impacts the wireless quality. SNR drives which type of modulation is used. It is not the ratio but different between level of noise and the signal received or broadcasted by the AP. Every vendor calculates SNR differently.

Signal strength vs Noise

Channel utilization – High density environments normally tend to have channel utilization. It reflects the statistics of the environment. How busy our channels are? Also tells when CCI becomes an issue. Turn off some 2.4 radios, lower or higher the power depending on the kind of issue. Data rate – helps in troubleshooting wireless issues. Disable low data rates in the environment. Can disable 1,2, 5.5 data’s rates. Also not advisable to enable high data rate like 24 or 48Mbps.

RETRANSMISSIONS– should not have more than 10% in the environment. Could be caused due to low data rates set in the environment. Hidden nodes can be cause for the issues. Device drivers are also a cause of concern. Retry packet are sent at low data rate. Use Wireshark to track the retry packets. More retires not a healthy environment.

TIMERS– how long does it take the device to associate with AP. One of the metrics to determine. Longer time to join can be an issue. Band steering being enabled 2.4 responses can be delayed and association time will increase. AP that are broadcasting on dfs channels, some client devices do not scan AP on dfs channel. Authentication time also can be slower due to slow responses from radius server. Time to roam can also be factor. This can impact voip/rts traffic.

Limit active SSIDs to <5 : This is a general rule-of-thumb, and should be adjusted based on the vendor/environment and network design and performance requirements. Lower this value even further if you plan on deploying voice over Wi-Fi, perhaps down to 3 or 4 SSIDs max. Useful link

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