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5 GHz (802.11a)
The Cisco Unified Wireless IP Phone 7925G Series supports Dynamic Frequency Selection (DFS) and Transmit Power Control
(TPC) from 802.11h, which are required when using channels operating at 5.25 - 5.725 GHz, which are 15 of the 23 possible
channels.
DFS dynamically instructs a transmitter to switch to another channel whenever radar signal is detected. If the access point
detects radar, the radio on the access point goes on hold for at least 60 seconds while the access point passively scans for
another usable channel.
TPC allows the client and access point to exchange information, so that the client can dynamically adjust the transmit power.
The client uses only enough energy to maintain association to the access point at a given data rate. As a result, the client
contributes less to adjacent cell interference, which allows for more densely deployed, high-performance wireless LANs.
Lower power on the client provides longer battery life because less power is used by the radio.
5 GHz channels overlap their adjacent channel, so there should be at least 1 channel of separation for adjacent access points.
Using Dynamic Frequency Selection (DFS) on Access Points
For autonomous solution access points, select Dynamic Frequency Selection (DFS) to use auto channel selection.
When DFS is enabled, enable at least one band (bands 1-4).
For unified access points, enable Auto RF unless there is an intermittent interferer in an area which select access points can have
the channel statically assigned.
In case of radar activity, have at least one access point per area that uses a non-DFS channel (UNII-1). This ensures that a
channel is available when an access point's radio is in its hold-off period while scanning for a new usable channel.
For autonomous access points, enable band 1 only which allows the access point to use only a UNII-1 channel.
For unified access points, can manually select a UNII-1 channel (channels 36, 40, 44, 48) for the desired access points.
A UNII-3 channel (5.745 - 5.805 GHz) can optionally be used if available.
Cisco Unified Wireless IP Phone 7925G Series Deployment Guide
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