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Cisco Aironet 1520, 1130, 1240 Series Wireless Mesh Access Points, Design and Deployment Guide, Release 6.0
OL-20213-01
Mesh Network Components
Note
Frequency depends on the regulatory domain in which the access point is installed. For additional
information, refer to the
Channels and Power Levels
http://www.cisco.com/en/US/docs/wireless/access_point/channels/lwapp/reference/guide/lw_chp2.html
Dynamic Frequency Selection
Previously, devices employing radar operated in frequency sub-bands without other competing services.
However, controlling regulatory bodies are attempting to open and share these bands with new services
like wireless mesh LANs (IEEE 802.11).
To protect existing radar services, the regulatory bodies require that devices wishing to share the newly
opened frequency sub-band behave in accordance with a protocol named Dynamic Frequency Selection
(DFS). DFS dictates that to be compliant, a radio devices must be capable of detecting the presence of
radar signals. When a radio detects a radar signal, it is required to stop transmitting to for at least 30
minutes to protect that service.The radio then selects a different channel to transmit on but only after
monitoring it. If no radar is detected on the projected channel for at least one minute then the new radio
service device may begin transmissions on that channel.
The process for a radio to detect and identify a radar signal is a complicated task that sometimes leads
to incorrect detects. Incorrect radar detections can occur due to a large number of factors, including due
to uncertainties of the RF environment and the ability of the access point to reliably detect actual
on-channel radar.
The 802.11h standard addresses DFS and Transmit Power Control (TPC) as it relates to the 5 GHz band.
DFS is to avoid interference with radar and TPC is used to avoid interference with satellite feeder links.
Note
DFS is mandatory in the US for frequency bands 5250 to 5350, and 5470 to 5725. DFS and TPC are
mandatory for these same bands in Europe. (See
.)
provides a summary of those regulatory domains that require DFS support.
Table 3
Frequency Band
Frequency Band Terms
Description
Model Support
UNII-1
1
1.
UNII refers to the Unlicensed National Information Infrastructure.
Regulations for UNII devices operating in
the 5.15 to 5.25 GHz frequency band.
Indoor operation only,
1130, 1240
UNII-2
Regulations for UNII devices operating in
the 5.25 to 5.35 GHz frequency band.
DFS and TPC are mandatory in this band.
1130, 1240, 1522
UNII-2 Extended
Regulations for UNII-2 devices operating
in the 5.470 to 5.725 frequency band.
1130, 1240, 1522
ISM
2
2.
ISM refers to Industrial Science and Mechanical.
Regulations for UNII devices operating in
the 5.725 to 5.850 GHz frequency band.
1130, 1240, 1522, 1524