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Configuring Short Slot Time to Improve WiFi Performance

Wireless, much like all other networking technologies, has many different settings you can tweak. From my experience though just changing any setting without understanding or testing could cause problems.

Like I always say, “Network settings are like a bag of nails; you can use them productively, or you can cause some real damage. The difference being you knowing how to use them properly.

In this specific example, one of customers asked me about changing the Short Slot Time setting in his access point. When I asked why he said that he read online that changing this setting should result in better performance. Skeptically I asked, “How are you planning to test this?”. After surveying his ‘deer in the headlight” look, I assumed he isn’t going to test anything. Then he responded that honestly he was going to change it, and then see if the number of WiFi performance calls decrease.

I explained what Short Slot Time does and showed him what Cisco says in its AP configuration help screen:

“Short Slot Time

When you enable short slot time, only the wireless devices with clients associated to the 802.11g, 2.4-GHz radio support slot time. Enabling short slot time increases throughput on the 802.11g, 2.4-GHz radio.”

In this environment his AP and clients support Short Slot Time, are on 2.4 Ghz and configured for 802.11g – perfect!!

I suggested we conduct some iperf tests with Short Slot Time disabled and enable. I chose iperf because this setting is supposed to improve performance, so iperf is perfect.

We ran 5 iperf tests, dropped the highest/lowest speeds and averaged the remaining 3. We repeated this a few more times.

From this limited testing, we found that with Short Slot Time enabled we saw an average of 1 Mbps increase in performance.

Please remember that I’m not asking you to blindly turn this setting on, or that if you have this setting enabled, you automatically get better performance. I would rather you walk away with the methodology and way in which we proved this setting benefitted this customer.



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