IEEE 802.11b Supplement to 802.11 Standards

IEEE 802.11b Supplement to 802.11 Standards
The IEEE’s 802.11b supplement to the original 802.11 standards defined today’s most common
wireless standard, Wireless Fidelity (Wi-Fi). It is also known as 802.11 High Rate, and supports
speeds of up to 11 Mbps (comparable to the 10-Mbps speed of the original 802.3 Ethernet standard)
[466]. The 802.11b operates in the same 2.4-GHz band as 802.11. Until the 802.11b, IEEE 802.11
networks operated at speeds of only 1 or 2 Mbps. The 802.11b’s rapid rise in popularity is basically
due to its faster data transmission rate: No longer was wireless the slower technology to standard
Ethernet. Work could be done approximately as quickly on a wireless network as was being done on a wired standard Ethernet. Since the 802.11b is more widely embraced by commercial enterprisers,
it became affordable for home networks.
It is important to realize that 802.11b only defines a new kind of PHY and MAC sublayer for
802.11, not an entirely new approach to wireless communications. The LLC sublayer (of the OSI data
link layer) does not need to be changed by 802.11b (this is consistent with the IEEE 802 reference
model). However, 802.11b does introduce two new sublayers into the PHY: the PHY convergence
procedure (PLCP) sublayer, and the physical medium dependent (PMD) sublayer. The PMD sublayer
provides a means and method of transmitting and receiving data through a wireless medium between
two or more STAs, each using the high-rate (11 Mbps) system [467]. The PLCP sublayer allows the
MAC to operate with minimum dependence on the PMD sublayer by facilitating the provision of MAC
services (such as the asynchronous data transfer service, which handles the transport of MSDUs) [467].
Another prominent refinement introduced by 802.11b concerns data transmission procedures.
The original 1997 802.11 standards support two entirely different methods of encoding – FHSS and
DSSS – in order to grant some flexibility to implementers. As it turns out, this led to confusion and
incompatibility between equipment. The 802.11b upgrade dropped FHSS in favor of DSSS. The DSSS
has proven to be more reliable than the FHSS, and settling on one method of encoding eliminates
the problem of having a single standard that includes two kinds of equipment that are not compatible
with each other. Turning away from the FHSS, of course, means that the 802.11b devices are not
backward compatible with the 802.11 devices using the FHSS. They are backward compatible with
the 802.11 devices using the DSSS, and because nothing has changed in the LLC sublayer, they can
operate in harmony with the standard wired Ethernet technology. The 802.11b looks like Ethernet to
user applications [465]. IEEE gives a special name to the 802.11b DSSS: high-rate direct-sequence
spread spectrum (HR/DSSS).