Cisco Systems OL-6415-04 manual DFS Automatically Enabled on Some 5-GHz Radio Channels

Chapter 2 Configuring Radio Settings

Configuring Radio Channel Settings

DFS Automatically Enabled on Some 5-GHz Radio Channels

Access points with 5-GHz radios configured at the factory for use in Europe now comply with regulations that require radio devices to use Dynamic Frequency Selection (DFS) to detect radar signals and avoid interfering with them. Radios configured for use in other regulatory domains do not use DFS.

When a DFS-enabled 5-GHz radio operates on one of the 15 channels listed in Table 2-7, the access point automatically uses DFS to set the operating frequency.

Note You cannot manually select a channel for DFS-enabled 5-GHz radios.

Table 2-7 DFS Automatically Enabled on these 5-GHz Channels

5-GHz Channels on Which DFS is Automatically Enabled

52 (5260 MHz)	104 (5520 MHz)	124 (5620 MHz)
56 (5280 MHz)	108 (5540 MHz)	128 (5640 MHz)
60 (5300 MHz)	112 (5560 MHz)	132 (5660 MHz)
64 (5320 MHz)	116 (5580 MHz)	136 (5680 MHz)
100 (5500 MHz)	120 (5600 MHz)	140 (5700 MHz)

When DFS is enabled, the access point monitors its operating frequency for radar signals. If it detects radar signals on the channel, the access point takes these steps:

•Blocks new transmissions on the channel.

•Flushes the power-save client queues.

•Broadcasts an 802.11h channel-switch announcement.

•Disassociates remaining client devices.

•Randomly selects a different 5-GHz channel.

•If the channel selected is one of the channels in Table 2-7, scans the new channel for radar signals for 60 seconds.

•If there are no radar signals on the new channel, enables beacons and accepts client associations.

Note The maximum legal transmit power is greater for some 5-GHz channels than for others. When it randomly selects a 5-GHz channel on which power is restricted, the access point automatically reduces transmit power to comply with power limits for that channel.

Note We recommend that you use the world-mode dot11d country-codeconfiguration interface command to configure a country code on DFS-enabled radios. The IEEE 802.11h protocol requires access points to include the country information element (IE) in beacons and probe responses. By default, however, the country code in the IE is blank. You use the world-modecommand to populate the country code IE.

Cisco Wireless ISR and HWIC Access Point Configuration Guide

OL-6415-04 2-19