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Cisco Wireless IP Phone 7920 Administration Guide for Cisco CallManager Release 3.3 or Later
OL-3930-02
Chapter 1 An Overview of the Cisco Wireless IP Phone 7920
Understanding the Voice Wireless Network
Figure 1-2 Wireless LAN with Cisco Wireless IP Phone 7920s
The 802.11 Standard for Wireless LAN Communications
Wireless LANs must follow the Institute of Electrical and Electronics Engineers
(IEEE) 802.11 standards that define the protocols that govern all Ethernet-based
wireless traffic. The 802.11b sub-standard is the most prevalent standard in
wireless 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 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
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