The original 802.11 standard had two variationsboth offering the same speeds but differing in the RF spread spectrum used. One of the 802.11 used FHSS. This 802.11 variant used the 2.4GHz radio frequency band and operated with a 1 or 2Mbps data rate. Since this original standard, wireless implementations have favored DSSS.
The second 802.11 variation used DSSS and specified a 2Mbps-peak data rate with optional fallback to 1Mbps in very noisy environments. 802.11, 802.11b, and 802.11g use the DSSS spread spectrum. This means that the underlying modulation scheme is very similar between each standard, enabling all DSSS systems to coexist with 2, 11, and 54Mbps 802.11 standards. Because of the underlying differences between 802.11a and the 802.11b/g, they are not compatible.
Table 8 summarizes each of the wired standards discussed in the previous sections.
Table 8 IEEE 802 Wireless Network Standards
IEEE Standard
Frequency/Media
Speed
Topology
Transmission Range
Access Method
Spread Spectrum
802.11
2.4GHz RF
1 to 2Mbps
Ad-hoc/infra-structure
CSMA/CA
DSSS
802.11
2.4GHz RF
1 to 2Mbps
Ad-hoc/infra-structure
CSMA/CA
FHSS
802.11a
5GHz
Up to 54Mbps
Ad-hoc/infra-structure
25 to 75 feet indoors range can be affected by building materials
CSMA/CA
OFDM
802.11b
2.4GHz
Up to 11Mbps
Ad-hoc/infra-structure
Up to 150 feet indoors; range can be affected by building materials
CSMA/CA
DSSS
802.11g
2.4GHz
Up to 54Mbps
Ad-hoc/infra-structure
Up to 150 feet indoors; range can be affected by building materials
CSMA/CA
DSSS
IrDA
Infrared light beam
Up to 16Mbps
Ad-hoc
1 meter
N/A
N/A
Bluetooth
2.4GHz RF
720Kbps
Ad-hoc
10 meters
N/A
FHSS