164
Networking Fundamentals
Wi-Fi
a term coined by the
Wi-Fi Alliance that
refers to 802.11 wire-
less network products.
24 Mbps, 18 Mbps, 12 Mbps, 9 Mbps, and 6 Mbps. At the 5-GHz frequency, 802.11a
networking devices are not susceptible to interference from devices that cause
interference at the 2.4-GHz frequency range. 802.11a devices are incompatible with
802.11b and 802.11g devices. Also, 802.11a devices use a higher frequency than 802.11b
or 802.11g devices. The higher frequency cannot penetrate materials such as building
walls like the lower frequency devices can. This results in 802.11a devices having a
shorter range when compared with 802.11b, 802.11g, and 802.11n devices.
802.11b
Although the 802.11a and 802.11b standards were developed at the same time,
802.11b was the fi rst to be adopted by industry. The maximum data rate for 802.11b
is 11 Mbps. When the highest rate cannot be achieved because of distance or radio
interference, a lower rate is automatically selected. The lower rates are 5.5 Mbps,
2 Mbps, and 1 Mbps. An 802.11b device can operate over any of 11 channels
within the assigned bandwidth. When communicating between wireless devices,
all devices should use the same channel. When using devices from the same
manufacturer, the same channel is automatically selected by default. Two wireless
networks, one constructed of 802.11b devices and the other constructed of 802.11a
devices, can coexist without interfering with each other because they use different
assigned frequencies. This allows for two different wireless networks to operate
within the same area without interfering with the other.
802.11 network devices are often referred to as Wi-Fi, which stands
for “wireless fi delity.” The use of the term Wi-Fi was due to manufacturers
forming the Wireless Ethernet Compatibility Alliance (WECA) in an effort to
standardize wireless network devices. Devices approved as compatible with
Figure 4-17.
IEEE 802.11
standards and their
characteristics.
802.11a 5 GHz 5.15 GHz– 6 Mbps 50 m OFDM
5.825 GHz 9 Mbps
12 Mbps
18 Mbps
24 Mbps
36 Mbps
54 Mbps
802.11b 2.4 GHz 2.4 GHz– 1 Mbps 100 m DSSS
2.4835 GHz 2 Mbps
5.5 Mbps
11 Mbps
802.11g 2.4 GHz 2.4 GHz– 1 Mbps 100 m DSSS
2.4835 GHz 2 Mbps
5.5 Mbps
11 Mbps
5 GHz 5.15 GHz- 54 Mbps 50 m OFDM
5.825 GHz
802.11n 2.4 GHz 2.4 GHz– All previous data 300 m OFDM
2.4835 GHz rates up to
300 Mbps and
5 GHz 5.15 GHz- possibly as high
5.825 GHz as 600 Mbps
802.11 Radio Frequency
Data Rate
Range Transmission
Standard Frequency Range (approximate) Method