IEEE 802.11 Standards for Wireless Networks

IEEE 802.11 Standards for Wireless Networks
The Institute of Electrical and Electronics Engineers (IEEE) develops and maintains technological
standards based on the recommendations of individuals with expertise in the technology being standardized.
Scientists, manufacturers, and end-users provide input to the institute, which comes to
a consensus about the standards suitable for a particular technology. Use of an IEEE Standard is
wholly voluntary and the existence of an IEEE Standard does not imply that there are no other ways
to produce, test, measure, purchase, market, or provide other goods and services related to the scope
of the IEEE Standard [452]. Research scientists, manufacturers, and end-users all benefit from the
shared specifications contained in the standards. When everyone uses the standard, customers can use
equipment from different manufacturers with no incompatibilities.
The IEEE 802 set of standards has to do with the physical layer (PHY) and data link layers of local
and metropolitan area networks (LANs and MANs). These are the bottom two layers in the ISO/OSI
networking model, far removed from the application layer, and are concerned with data transmission
(and reception) between computers in LANs and MANs. The IEEE has split the data link layer into
two different sublayers: logical link control (LLC) and media access control (MAC) (see Figure 4.1).
The IEEE LLC protocol concerns the logical address, control information, and data portions of an
HDLC (high-level data link control) frame, while the MAC protocols deal with synchronization, error
control (EC), and physical addresses. MAC protocols are specific to the LAN using them (Ethernet,
Token Ring, Token Bus, etc.) [455].
The IEEE 802.3 standards are concerned with Ethernet (wired) communications. Originally, they
supported 10-Mbps data rates, but as network terminals became faster and thus capable of running
multimedia applications, and as the need to share high-speed servers among LANs became widespread,
faster data rates were included in the standards. They were updated in the mid-1990s to include “fast
Ethernet” transmission rates of 100 Mbps, and in the late 1990s the Gigabit Ethernet was standardized  under 802.3 [454]. Experts attest that the two major driving forces of this industry have always been
the ease of installation and increase of data rate, the two important characteristics of Fast Ethernet
and Gigabit Ethernet. Thus, Ethernet dominated over other 802.3 LAN IEEE standards (the so-called
Token Ring and Token Bus).
The 802.4 and 802.5 standards concern the PHY and MAC layers for Token Bus and Token Ring
topologies, respectively. IEEE’s 802.6 standards address the needs of MANs [454]. The 802.11 family
of standards is devoted to the requirements of the bottom two ISO layers in wireless networks (wireless
local-area networks (WLANs)). A complete list of the rest of the standards is given in Table 4.1.
When developing the standards for wireless networks, the IEEE observed the radio frequency
regulations of the US Federal Communications Commission (FCC), since radio waves were the
transmission medium of choice for wireless networking. In 1985, the FCC designated certain portions
of the radio frequency spectrum for industrial, scientific, and medical use, and these became known
as the ISM bands; they are: (1) 902–928 MHz, a bandwidth of 26 MHz; (2) 2.4–2.4835 GHz, a
bandwidth of 83.5 MHz, commonly called the 2.4-GHz band; and (3) 5.725–5.850 GHz, a bandwidth
of 125 MHz, commonly called the 5-GHz band.
Within certain guidelines, the FCC’s regulations allow users to operate radios inside these bands
without an FCC licence, an obvious boon for the developers of wireless network technology (and for
the users who do not have to obtain a licence to operate their cell phones) [453].
The 802.11 standards have evolved over time, and presently six methods for wireless data transmission
are defined in the 802.11 standards. Each means of transmission represents its own PHY
within 802.11. The first IEEE 802.11 standards were completed in 1997, and defined three of these
PHY for 1- and 2-Mbps data rates. An overview of these PHY is provided in Table 4.2 and also
explained as follows:
• The Direct-Sequence Spread Spectrum (DSSS)1 PHY uses the 2.4-GHz band and can transmit
data at 1 or 2 Mbps. It was first used for military communications. To prevent jamming,
and, to a lesser extent, eavesdropping, radios that use DSSS transmit their signals across the
entire available ISM band at very low power. This prevents interference from narrowband
signals (jammers or others) and lessens the likelihood of transmission errors. Eavesdroppers
may interpret these signals as background noise [452, 453].
• The Frequency Hopping Spread Spectrum (FHSS) PHY also uses the 2.4-GHz band for transmission
at 1 or 2 Mbps, and also originated in military applications. Two communicating radios
802.1 Higher-layer LAN protocols
802.2 Logical link control
802.3 Ethernet (wired)
802.4 Token Bus
802.5 Token Ring
802.6 MAN
802.7 Broadband
802.8 Fiber optic
802.9 Isochronous LAN
802.10 LAN/MAN Security
802.11a Wireless LAN: 5-GHz band
802.11b Wireless LAN: 2.4-GHz band
802.11c Wireless LAN: higher layers
802.11d Wireless LAN: MAC
802.11e Wireless LAN: MAC
802.11f Higher layers
802.11g Wireless LAN: higher rate 2.4-GHz band
802.11h Wireless LAN: MAC
802.11i Wireless LAN: MAC
802.12 Demand priority
802.13 Not used
802.14 Cable modem
802.15 Wireless PAN
802.16 Broadband wireless access
802.17 Resilient packet ring
802.18 Radio regulations
802.19 Coexistence
802.20 Mobile broadband wireless access

802.11 PHY layers
DSSS 2.4 GHz 1 or 2 Mbps
FHSS 2.4 GHz 1 or 2 Mbps
DFIR 850 to 950 nm (infrared) None implemented
COFDM 5 GHz 54 Mbps
HR/DSSS 2.4 GHz 5.5 or 11 Mbps
OFDM 2.4 GHz 54 Mbps
using FHSS change frequencies according to a predetermined pseudorandom pattern, and only
remain on a given frequency for a split second (FCC regulations require the frequency hops to
take place in 400 ms or less). This technique minimizes the chances that more than one radio
device will be transmitting on the same frequency at the same time. If a sender happens to
detect interference from another radio at a particular frequency, it retransmits its data after the
next hop to a new frequency [453]. FHSS was phased out of 802.11 in the 802.11b standards.
• The Diffused Infrared (DFIR) PHY uses near-visible light in the 850-nm to 950-nm range for
signaling [452]. However, unlike infrared (IR) TV remote controls that need a line of sight to work, devices that follow the 802.11 DFIR standards do not need to be aimed at one another,
permitting the construction of a true LAN [452]. But, there are no wireless networking products
currently available that implement this PHY [453]. One potential source of interference when
using this technology would be a human being walking between a PC and its printer when they
were trying to communicate.
• A fourth 802.11 PHY is defined by IEEE’s 802.11a standards: The Coded Orthogonal Frequency
Division Multiplexing (COFDM) layer is capable of transmitting data at 54 Mbps by
using the broader 5-GHz band. However, FCC regulations limit the transmission power used
at these higher frequencies, and thus it reduces the distance higher-frequency transmissions
can travel. For these reasons, radios that use COFDM technology must be closer together than
those using the other PHY introduced above. The obvious benefit of COFDM is speed. The
IEEE 802.11a standards are further discussed in Section 4.2.
• The IEEE 802.11b standards cover the fifth PHY, the High-Rate Direct-Sequence Spread Spectrum
(HR/DSSS) layer. Using this layer, data can be transmitted at 5.5 or 11 Mbps, rivaling the
standard Ethernet rate of 10 Mbps, and it has become the most widely used IEEE 802.11 PHY
despite its recent entry onto the scene in 1999. HR/DSSS technology is an extension of DSSS
technology and is designed to be backward compatible with its predecessor (both operate in the
2.4-MHz band) [453]. Further discussion on the 802.11b standards is presented in Section 4.1.7.
• The sixth 802.11 PHY is detailed in the IEEE 802.11g standards and is backward compatible
with 802.11b. The Orthogonal Frequency Division Multiplexing (OFDM) PHY allows 54 Mbps
data rates in the 2.4-MHz band. The speed of transmission under OFDM and COFDM is sufficient
to carry voice and image data fast enough for most users. More on the IEEE 802.11g
standards is given in Section 4.1.8.