Cisco Cisco Prime Network Control System Appliance White Paper

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Features That Improve Channel Bandwidth for Cisco Cius

Spectrum Intelligence is the recommended tool to manage bandwidth robbing interference. There are three other

Cisco features that help provide better 2.4-GHz channel bandwidth.

Cisco BandSelect Technology

Cisco BandSelect makes use of the channels and bandwidth available in the 5-GHz Wi-Fi band. This feature

directs a client that is capable of using both Wi-Fi bands to associate to the access point on the 5-GHz band. This

does two things for the 2.4-GHz band: it provides more bandwidth for the access point and reduces co-channel

interference for nearby access points.

Cisco ClientLink Technology

Cisco ClientLink technology is available on all Cisco 802.11n Aironet access points. Cisco recommends that you

enable ClientLink on both the 2.4-GHz and 5-GHz bands. This beam-forming feature reduces retries by 50 percent

for 11g and 11a video call transmissions, thereby increasing bandwidth while reducing jitter. For ClientLink to work,

each of the three receive radios per band on the access point must receive the client signal with similar signal

strength, which, in turn, requires the attached antennas to be the same and in the same location. Cisco antennas

are recommended for beam-forming support that provides optimum signal-to-noise (SNR) at the client radio.

Maximum Ratio Combining Technology

Cisco access points use three antennas to process received signals into one reinforced signal by adjusting their

phases and amplitudes to form the best possible signal. The algorithm it uses, called maximal ratio combining

(MRC) helps in the uplink direction, enabling the access point to

“hear” the client better. MRC helps to provide to

provide the optimal SNR at the access point.

Removing Legacy 802.11 Data Rates to Increase Channel Bandwidth

Increased Bandwidth

The most effective way to increase channel bandwidth in the 2.4-GHz band is to remove legacy data rates. Access

point density can only be increased to a point with legacy data rates enabled before co-channel interference

reduces bandwidth. Co-channel interference is Wi-Fi traffic from nearby client devices and access points. To

improve 2.4-GHz bandwidth, Cisco recommends that you evaluate the number on clients in your network that are

not 802.11g-capable.

802.11g was ratified in 2003 and clients that are compliant with the IEEE standard were introduced in 2001. With

10 years of orthogonal frequency division multiplexing (OFDM) modulation clients, there may be no need to

support the legacy 802.11 and 802.11b data rates, particularly in enterprise and education settings. A configuration

without legacy data rates reduces co-channel interference, greatly increasing bandwidth in dense access point

deployments. There is virtually no reason to have 1 Mbps enabled or required.

Reviewing the list of clients associated on your Cisco Wireless LAN Controller (WLC) reveals which clients are

802.11 or 802.11b. Removing the 802.11 1-Mbps and 2-Mbps data rates has changed the channel utilization from

40 percent to 5 percent at sites with 35 foot access point spacing. At a channel utilization of 35 percent, the

channel is so busy that 802.11 back-off algorithms are in effect for virtually all packets to be transmitted, regardless

of 802.11e quality-of-service (QoS) configurations.