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May ❘ June 2001 IT Pro 17

IEEE 802.11: Moving

Closer to Practical

Wireless LANs

William Stallings

ireless LANs have quickly be-

come a significant niche in the

LAN market. As adjuncts to

traditional wired LANs, they sat-

isfy mobility, relocation, and ad hoc networking

requirements and provide a way to cover loca-

tions that are difﬁcult to wire.

As the name suggests, a wireless LAN uses a

wireless transmission medium. Until relatively

recently, few organizations used wireless LANs

because they cost too much, their data rates were

too low,they posed occupational safety problems

because of concerns about the health effects of

electromagnetic radiation, and the spectrum used

required a license. Today, however, these prob-

lems have largely diminished, and wireless LAN

popularity is skyrocketing.

WHEN WIRELESS LANs MAKE SENSE

Wireless LAN products first appeared in the

late 1980s, marketed as substitutes for traditional

wired LANs.The idea was to use a wireless LAN

to avoid the cost of installing LAN cabling and

ease the task of relocating or otherwise modify-

ing the network’s structure.

As events unfolded, however,

organizations began to rethink

this substitution strategy. LANs

had become more popular, and

architects were designing new

buildings to include extensive

prewiring for data applications.

Also, as data transmission tech-

nology advanced, organizations

began relying more on inexpensive twisted-pair

cabling for LANs—in particular Category 3 and

Category 5 unshielded twisted pair. Category 3

wiring is the traditional telephone wiring found

in every office building; category 5 wiring is

higher-performance wiring able to carry higher

data rates. Many older buildings are prewired

with an abundance of Category 3 cable, and many

newer buildings are prewired with Category 5.

Thus, there was little motivation to replace wired

LANs with wireless.

This is not true of all environments, how-

ever. For some, the motivation to use wireless

LANs is much higher. Buildings with large open

areas, such as manufacturing plants, stock

exchange trading floors, and warehouses, make

wired LANs awkward to install because of lim-

ited choices for cable placement. Historical build-

ings often have insufﬁcient twisted-pair cabling

and prohibit drilling holes for new wiring.Finally,

small ofﬁces often ﬁnd it uneconomical to install

and maintain wired LANs.

POSSIBLE CONFIGURATIONS

In most cases, an organization already has a

wired LAN to support servers and some station-

ary workstations. For example, a manufacturing

facility typically has an ofﬁce area that is physi-

cally separate from the factory ﬂoor but must be

linked to it for networking.Therefore, organiza-

tions will commonly link a wireless LAN into a

wired LAN on the same premises. This kind of

application, or LAN extension, can take several

forms.

Although the IEEE 802.11 standard

has been around since 1997, work

continues to make it more adaptable

to the demand for higher data rates

and true wireless ﬂexibility.

What Is the

MAC Protocol?

Resources

Inside

1 2 3 4 5 6 7

Résumé du contenu

Page 1 - Wireless LANs

Page 2 - LAN conﬁguration

18 IT Pro May ❘ June 2001NETWORKSSingle and multiple cellsFigure 1 shows the single-cell conﬁguration—a simplewireless LAN strategy typical of many en

Page 3 - Career Service Center

likely to operate in close proximity.Consequently, a device assigned to one LANmay be able to transmit or receive withoutauthorization on a nearby LAN

Page 4 - Figure 2. IEEE’s 802.11’s

20 IT Pro May ❘ June 2001NETWORKSbility is also an imperative because applications evolveand requirements change.Recognizing the need to balance these

Page 5 - Figure 3. IEEE’s 802.11’s

May ❘ June 2001 IT Pro 21The infrared option never gained market support becauseit requires unobstructed line-of-sight and because the avail-able dat

Page 6

22 IT Pro May ❘ June 2001NETWORKSout over time, which minimizes effects from interferenceand degradation.Most of the early 802.11 networks used the FH

Page 7 - Resources

May ❘ June 2001 IT Pro 23The 802.11b speciﬁcation quickly led to product offer-ings, including chip sets, PC cards, access points, and sys-tems. Appl