Wireless Modulation Technologies; Ap, Channel, And Domain Relationships - Cisco 7925G Administration Manual
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VoIP Wireless Network
1 Tx power: Adjusts dynamically when associating with an AP if the AP client setting is enabled.
Note
2 Data rate: Advertised rates by the APs are used. If the Restricted Data Rates functionality is enabled
in the Cisco Unified Communications Manager Administration phone configuration, then the Traffic
Stream Rate Set IE (Cisco Compatible Extensions [CCX] V4) is used.
Wireless Modulation Technologies
Wireless communications use the following modulation technologies for signaling:
Direct-Sequence Spread Spectrum (DSSS)
Orthogonal Frequency Division Multiplexing (OFDM)
The following table provides a comparison of data rates, number of channels, and modulation technologies
by standard.
Table 8: Data Rates, Number of Channels, and Modulation Technologies by IEEE Standard
Item
Data rates
Nonoverlapping
channels
Wireless modulation
AP, Channel, and Domain Relationships
APs transmit and receive RF signals over channels within the 2.4 GHz or 5 GHz frequency band. To provide
a stable wireless environment and reduce channel interference, you must specify nonoverlapping channels
for each AP. The recommended 2.4 GHz channels to be used are 1, 6, and 11.
Regulatory domains determine the number of channels that wireless communications can use within the
frequency band.
Prevents interference by spreading the signal 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 identifies the data packets for the device and all other
data packets are ignored. Cisco wireless 802.11b/g products use DSSS technology to support multiple
devices on the WLAN.
Transmits signals by using RF. OFDM is a physical-layer encoding technology that breaks one high-speed
data carrier into several lower-speed carriers to transmit in parallel across the RF spectrum. When used
with 802.11g and 802.11a, OFDM can support data rates as high as 54 Mbps.
802.11b
1, 2, 5.5, 11 Mbps
3 (Japan uses 4)
DSSS
Radio Frequency Ranges, on page 25
Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G Administration Guide
Wireless Modulation Technologies
802.11g
6, 9, 12, 18, 24, 36, 48,
54 Mbps
3
OFDM
list the frequency ranges, operating channels, and
802.11a
6, 9, 12, 18, 24, 36, 48,
54 Mbps
Up to 23
OFDM
29
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