H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 493)

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Configuring WLAN RRM
Radio overview
Radio frequency (RF) refers to electrical signals that can be transferred over the space to a long distance.
802.11b/g in the IEEE 802.11 standards operates at the 2.4 GHz band, 802.11a operates at the 5 GHz
band, and 802.11n operates at both the 2.4 GHz and 5 GHz bands. Radio frequency is allocated in
bands, each of which corresponds to a range of frequencies.
WLAN RRM overview
WLAN radio resource management (RRM) is a scalable radio resource management solution. APs
collect radio environment information in real time. The AC analyzes the collected information. The AC
makes radio resource adjustment configurations according to analysis results. APs implement the
configurations made by the AC for radio resource optimization. Therefore, through information collection,
information analysis, decision-making, and implementation, WLAN RRM delivers a real-time, intelligent,
and integrated radio resource management solution. This enables a WLAN network to quickly adapt to
radio environment changes and remain in a healthy state.
Dynamic frequency selection
A WLAN has limited working channels. Channel overlapping can easily occur. In addition, other radio
sources such as radar and micro-wave ovens might interfere with the operation of APs. Dynamic
frequency selection (DFS) can solve these problems.
With DFS, the AC selects an optimal channel for each AP in real time to avoid co-channel interference
and interference from other radio sources.
The following conditions determine DFS:
• Error code rate—Physical layer error code and CRC errors.
• Interference—Influence of 802.11 and non-802.11 wireless signals on wireless services.
• Retransmission—APs retransmit data if they do not receive ACK messages from the AC.
• Radar signal detected on a working channel—The AC immediately notifies the AP to change its
working channel.
If the first three conditions are met, the AC calculates the channel quality. The AP does not use the new
channel until the channel quality difference between the new and old channels exceeds the tolerance
level.