In a turbulent Wireless environment, guard interval can certainly add value and provide more resiliance to the overall wireless environment. First up, we need to understand, what i guard-interval and what does it do? Guard Interval Introduction Any environment where the probability of the delay spread being high is there needs to be extra careful when opting for SGI. The maximum resilience we can provide in such cases, the better. In Cisco environmet, GUI doesnt have the option to change the GI, even WLC CLI doesnt have that option explicitly. However, there is a way to change that inside the AP. The default setting is to use "Any" ie SGI/LGI, auto acceptance of GI parameter, depending on the environment and thats how i would recommend to leave it to be. As we can see the default value is "Any". By default, for any 802.11n capable environment this allows usage of SGI. However, if we see a lot of failing interference index, failing noise profile, lots of retries and low throughput, it would be a good idea to check for SGI and ensure that the RF is clear. Using a Spectrum analyzer or using a Channel analyzer should help in identifying the source of interference. If we can take it out, thats the best outcome but if we cant then using the LGI option will provide more tolerance to the system. It may not be completely able to eradicate the issue but some resilience can still be induced in the system. Here is how you go along configuring it on the Cisco AP once you are logged inside the AP CLI - Post configuration we should be able to see the output as below - We can also verify the same config from Cisco WLC. For that we need to run the following command on the WLC to be able to access the AP from the WLC CLI - debug ap enable <AP Name> debug ap command "show controller do1 | in Guard-Interval" <AP Name> Upon further test i have noticed that changing one AP to LGI does not have any impact on other AP's in terms of them moving to LGI as well.
However, the AP i manually changed to LGI did revert to SGI as the other AP's. Comments are closed.
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