Wireless Access Points - Cisco 7920 Administration Manual

Understanding the Voice Wireless Network

Wireless Access Points

Cisco Wireless IP Phone 7920 Administration Guide for Cisco CallManager Release 3.3 or Later
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devices can communicate without interference. Each device has a special code
that it uses to identify its data packets and to ignore all others. The Cisco wireless
products use DSSS technology to support multiple devices on the WLAN.
The critical components in the wireless network are the access points (APs) that
provide the "hot spots" or wireless links to the network. Cisco requires that
Cisco IOS is running on the APs that support voice calls since Cisco IOS provides
features for managing voice traffic. The minimum version of IOS you can use is
12.2(15)JA. The Cisco Aironet APs that support IOS include the following AP
series:
• Cisco Aironet AP 350
Cisco Aironet AP 1100
•
• Cisco Aironet AP 1200
Each AP has a hard-wired connection to a network layer switch, such as a
Cisco Catalyst 4000, that is configured on the LAN. The switch provides access
to gateways and the Cisco CallManager server to support wireless IP telephone
(WIPT).
APs transmit and receive RF signals over channels within the 2.4 GHz frequency
band. Regulatory domains determine the number of channels that wireless
communications can use within the 2.4 GHz frequency band. The Cisco Aironet
APs support up to 11 communication channels in North America, 13 channels in
Europe (ETSI) and 14 channels in Japan. An access point broadcasts on a specific
channel within the available channel range. To provide a stable wireless
environment and reduce channel interference, you must specify non-overlapping
channels for each AP. The recommended channels are 1, 6, and 11.
The AP has a transmission range or coverage area that depends on its type of
antenna and transmission power. The access point coverage range is from 500 to
1000 feet with effective isotropic radiated power (EIRP) output that scales at 1, 5,
20, 50, and 100mW. To provide effective coverage, access points need a range
overlap of approximately 20 percent to allow uninterrupted connections as phone
users roam from one access point to another.
Chapter 1 An Overview of the Cisco Wireless IP Phone 7920
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