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Cisco Wireless IP Phone 7920 Administration Guide for Cisco CallManager Release 4.0 and 4.1
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Chapter 2 An Overview of the Wireless Network
Understanding the Wireless LAN
LAN communications and is commonly called WiFi. The 802.11b standard
specifies the radio frequency (RF) of 2.4 GHz for both transmitting and receiving
data at speeds of 1, 2, 5.5 and 11 Mbps.
The 2.4 GHz RF range is an open frequency range that does not require licensing.
Many devices operate in this bandwidth including cordless phones and microwave
ovens; consequently, wireless communication is susceptible to interference or
noise. Interference does not destroy the signal, but can impede the transmission
speed and reduce an 11 Mbps signal all the way down to a 1Mbps signal. In
addition, RF interference can reduce the voice quality over the wireless network.
To help prevent interference, direct-sequence spread spectrum (DSSS) technology
was developed to spread the signal out over the frequency range or bandwidth.
DSSS technology multiplexes chunks of data over several frequencies so that
multiple 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.
Connecting to the Wireless Network
The critical components in the wireless network are the access points that provide
the wireless links (or “hot spots”) to the network. Cisco requires that the access
points supporting voice communications must run Cisco IOS Version 12.2(15)JA
or later. Cisco IOS provides features for managing voice traffic. The Cisco
Aironet Access Points that support IOS include the following access point series:
•
Cisco Aironet Access Point 350
•
Cisco Aironet Access Point 1100
•
Cisco Aironet Access Point 1200
Each access point 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 telephony
(WIPT).
Access points 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 Access Points support up to 11 communication channels in North
America, 13 channels in Europe (ETSI) and 14 channels in Japan. An access point
Содержание 7920 - Unified Wireless IP Phone VoIP
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