Cisco Cisco Aironet 3700i Access Point 백서
© 2015 Cisco and/or its affiliates. All rights reserved. This document is Cisco Public Information.
Page 16 of 23
Figure 5 shows DBS in use.
Figure 5. Cisco DBS
To summarize, since DBS is constantly monitoring the channel and BSS statistics it is effectively evaluating
transient parameters (802.11n and 802.11ac client mix, load, and traffic flow types) and reacts to these
fast-
changing statistics by varying the BSS’s channel width. It adapts channel orientations that are unique and
introduced through 802.11ac, for example, select to whether transmit in 20, 40, or 80 MHz.
Flexible Dynamic Frequency Selection (DFS): Not All DFS Solutions Are Created Equally
5 GHz is a great place to operate a WLAN. There is ample spectrum, and it is far less crowded and noisy than
2.4 GHz.
However, the majority of 5-GHz spectrum is shared with radar (for both weather and military systems). Therefore,
Wi-Fi access points not only need to detect radar in order to avoid interference, but they also need to avoid being
an interferer to these systems. This procedure is commonly referred to as Dynamic Frequency Selection (DFS).
For DFS operation, if radar is detected on a channel then the access point must abandon that channel from further
operation for some minimum amount of time. Furthermore, the access point must ensure that any new channel it
selects for operation is free from radar (and that detection also requires a minimum amount of time).
Finally, accurate detection of radar (for example, avoiding false positives) also requires some skill. Compounding
the issue are many devices that emit radar-like transmissions (including Wi-Fi clients and access points doing
proprietary over-the-air detection and calibration).
As a result, many equipment vendors simply avoid use of the channels requiring DFS. Cisco believes we have an
ideal DFS solution, with a superior new feature we call Flexible Dynamic Frequency Selection (or for short,
FlexDFS).
In a historic DFS solution, it was assumed that the WLAN was typically operating using a 20 MHz channel. In this
case, only 20 MHz of spectrum would need to be abandoned if radar was detected.