Understanding 802.11ac and the option module
Figure 69 | Module antennas are internal to the Access Point and radiate |
Because the 5 GHz module operates in the same frequency band as the internal 5 GHz 802.11n radio, both radios have been purposefully designed to work in tandem (think of it as a blended radio) where both radios work as one radio maintaining proper isolation and performance. Unlike the competition, this allows the 802.11ac client to be serviced by the module while legacy a/g and 802.11n clients are serviced by the integrated radios taking full advantage of Client Link 2.0 to beam form without having to try and bounce clients around based on signal strength.
Given the AP has a dual core processor with one core managing the module, similar to the “master/slave” approach that was used with IDE hard drives, the module always takes its direction from the “master” radio, in this case the integrated 802.11n radio. So when performing power and frequency selection for example selecting 80 MHz (802.11ac) channel bonding, the integrate radio and not the module radio sets the “anchor” point where the frequency starts with the module performing the overlay extending the 80 MHz over the existing channel selected by the integrated “master” radio (802.11n radio). Both the integrated radio and the module also share the same SSIDs.
This virtual radio approach requires both radios to be enabled so you cannot disable the integrated 5 GHz radio and just run the .11ac radio module.
Currently in the US, there are 22 (20 MHz) channels, 9 (40 MHz) channels, and 4 (80 MHz) channels. 802.11ac
Let’s take a look at the frequencies available and how the channel bonding would work.
Figure 70 | Current channel allocation plan US Theater. |
Cisco Aironet Series 1600/2600/3600 Access Point Deployment Guide, Release 7.5
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