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Cisco Aironet Series 2700/3700 Access Points Deployment Guide
Cisco Aironet Series 3700 Access Point
Figure 76
Module Antennas are Internal to the Access Point and Radiate Omni-Directionally
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 ClientLink 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 which is 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. You cannot disable the integrated 5 GHz
radio and just run the .11ac radio module.
Client Band Steering
In order to optimize client performance, 802.11ac clients are able to take advantage of ECBF (Explicit
Compressed Beam-Forming)–a IEEE 802.11ac standardized method of Beam-forming–similar in some
ways to Cisco’s ClientLink but slightly different because the .11ac client needs to send “sounding
information” to the AP and then the AP uses that sounding information (from the client) to best send the
signal back to the client using beam-forming.
Note
ECBF only works with 802.11ac clients, Cisco ClientLink continues to be used with non-802.11ac
clients to improve the overall performance of 802.11n and legacy clients resulting in an improved
performance with all clients rather than just 802.11ac clients. This helps maintain solid connections to
the AP without having to bounce clients off of the AP using other methods such as signal strength
causing needless roaming with the client who is not actually engaged in passing traffic.
It is a significant advantage to allow the module to service the 802.11ac clients while the integrated radio
services the non-802.11ac clients. Should the 802.11ac client require something the module radio does
not support, (for example, Cisco Client Extensions “CCX elements”) the 802.11ac module will push the
client to the integrated radio to service that request.
