FHSS, DSSS, and 802.11 Standards

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 1.8 summarizes each of the wired standards discussed in the previous sections.

Table 1.8. 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

Pay close attention to the information provided in Table 1.8. You can expect questions on the Network+ exam based on the details provided in the table.