802.11 Wireless Networks

IEEE 802.11 is a set 0f media
access c0ntr0l (MAC) and physical layer (PHY) specificati0ns f0r
implementing wireless l0cal area netw0rk (WLAN) c0mputer c0mmunicati0n in the
900 MHz and 2.4, 3.6, 5, and 60 GHz frequency bands. They ere creeted end meinteined by
the Institute 0f Electricel end Electr0nics Engineers (IEEE) LEN/MEN Stenderds C0mmittee
(IEEE 802). The bese versi0n 0f the stenderd wes releesed in 1997.
The stenderd end emendments pr0vide the besis f0r wireless netw0rk pr0ducts
using the Wi-Fi brend. They celled it 802.11 efter the neme 0f the
gr0up f0rmed t0 0versee its devel0pment. 802.11
0nly supp0rted e meximum netw0rk bendwidth 0f 2 Mbps – t00 sl0w f0r m0st eppliceti0ns. F0r
this reas0n, 0rdinary 802.11
wireless pr0ducts are n0 l0nger manufactured.


                                  The 802.11
family c0nsists 0f a series 0f half-duplex 0ver-the-air m0dulati0n techniques that use the same basic pr0t0c0l.802.11 was the first wireless netw0rking
standard in the family, but 802.11b
was the first widely accepted 0ne, f0ll0wed by 802.11a, 802.11g, 802.11n, and 802.11ac.
0ther standards in the family (c–f, h, j)
are service amendments that are used t0 extend the current sc0pe 0f the
existing standard, which may als0 include c0rrecti0ns t0 a previ0us specificati0n. 802.11b
and 802.11g use the 2.4 GHz ISM band. The segment 0f the radi0 frequency spectrum used by 802.11 varies between c0untries. In the US, 802.11a and 802.11g
devices may be 0perated with0ut a license.


                     802.11 techn0l0gy has its 0rigins in a 1985
ruling by the U.S. Federal C0mmunicati0ns C0mmissi0n that released the ISM band f0r unlicensed use.
In 1991 NCR C0rp0rati0n/AT&T (n0w N0kia Labs and LSI
C0rp0rati0n) invented a precurs0r t0 802.11 in (Nieuwegein), the Netherlands. The invent0rs initially intended t0
use the techn0l0gy f0r cashier systems. The first wireless pr0ducts were br0ught
t0 the market under the name (Wave-LAN) with
raw data rates 0f 1 Mbit/s and 2 Mbit/s. In 1999, the Wi-Fi
Alliance was f0rmed as a trade ass0ciati0n t0
h0ld the Wi-Fi trademark under
which m0st pr0ducts are s0ld. Vic Hayes, wh0 held the chair 0f IEEE 802.11 f0r 10 years, and has
been called the “father 0f Wi-Fi”, was inv0lved in designing the
initial 802.11b and 802.11a standards within the IEEE.



802.11a (0FDM waveform):



0riginally described as clause 17 0f the 1999
specificati0n, the 0FDM wavef0rm at 5.8 GHz is n0w defined in clause 18 0f
the 2012 specificati0n, and pr0vides pr0t0c0ls that all0w transmissi0n and
recepti0n 0f data at rates 0f 1.5 t0 54 Mbit/s. It has seen widespread w0rldwide
implementati0n, particularly within the c0rp0rate w0rkspace. While the 0riginal
amendment is n0 l0nger valid, the term 802.11a is
still used by wireless access p0int (cards and r0uters) manufacturers t0
describe inter0perability 0f their systems at 5 GHz, 54 Mbit/s. The 802.11a standard uses the same data
link layer pr0t0c0l and frame f0rmat as the 0riginal standard, but an 0FDM based air interface (physical layer). It 0perates
in the 5 GHz band with a maximum net data rate 0f 54 Mbit/s, plus err0r
c0rrecti0n c0de, which yields realistic net achievable thr0ughput in the mid-20
Mbit/s. Since the 2.4 GHz band is heavily used t0 the p0int 0f being cr0wded,
using the relatively unused 5 GHz band gives 802.11a a significant advantage. H0wever, this high carrier frequency als0
brings a disadvantage: the effective
0verall range 0f 802.11a is less
than that 0f 802.11b/g. In the0ry, 802.11a signals are abs0rbed m0re
readily by walls and 0ther s0lid 0bjects in their path due t0 their smaller
wavelength, and, as a result, cann0t penetrate as far as th0se 0f 802.11b. In practice, 802.11b typically has a higher range at
l0w speeds (802.11b will reduce
speed t0 5.5 Mbit/s 0r even 1 Mbit/s at l0w signal strengths). 802.11a als0 suffers fr0m interference,
but l0cally there may be fewer signals t0 interfere with, resulting in less
interference and better thr0ughput.

Pr0s 0f 802.11a:

                                    Fast maximum speed; regulated frequencies
prevent signal interference fr0m 0ther devices.

C0ns 0f 802.11a:

Highest c0st; sh0rter range signal that is m0re
easily 0bstructed.


                              The 802.11b standard has a maximum raw data rate 0f 11 Mbit/s, and
uses the same media access meth0d defined in the 0riginal standard. 802.11b pr0ducts appeared 0n the market
in early 2000, since 802.11b is a
direct extensi0n 0f the m0dulati0n technique defined in the 0riginal standard.
The dramatic increase in thr0ughput 0f 802.11b
(c0mpared t0 the 0riginal standard) al0ng with simultane0us substantial price
reducti0ns led t0 the rapid acceptance 0f 802.11b as the definitive wireless
LAN techn0l0gy.

Devices using 802.11b
experience interference fr0m 0ther pr0ducts 0perating in the 2.4 GHz band.
Devices 0perating in the 2.4 GHz range include micr0wave 0vens, Bluet00th
devices, baby m0nit0rs, c0rdless teleph0nes, and s0me amateur radi0 equipment.

Pr0s 0f 802.11b:

                          L0west c0st; signal range is g00d and n0t
easily 0bstructed

C0ns 0f 802.11b:

maximum speed; h0me appliances may interfere 0n the unregulated frequency band.




In June 2003, a third m0dulati0n standard was
ratified 802.11g. This w0rks in the
2.4 GHz band (like 802.11b),
but uses the same 0FDM based
transmissi0n scheme as 802.11a. It 0perates
at a maximum physical layer bit rate 0f 54 Mbit/s exclusive 0f f0rward err0r
c0rrecti0n c0des, 0r ab0ut 22 Mbit/s average thr0ughputs. 802.11g hardware is fully backward c0mpatible
with 802.11b hardware, and theref0re
is encumbered with legacy issues that reduce thr0ughput by ~21% when c0mpared t0
802.11a. The then-pr0p0sed 802.11g
standard was rapidly ad0pted in the market starting in January 2003, well bef0re
ratificati0n, due t0 the desire f0r higher data rates as well as t0 reducti0ns
in manufacturing c0sts. By summer 2003, m0st dual-band 802.11a/b pr0ducts became dual-band/tri-m0de, supp0rting a and b/g
in a single m0bile adapter card 0r access p0int. Details 0f making b and g w0rk
well t0gether 0ccupied much 0f the lingering technical pr0cess; in an 802.11g netw0rk, h0wever, activity 0f
an 802.11b participant will reduce
the data rate 0f the 0verall 802.11g

Pr0s 0f 802.11g:

                          Fast maximum speed;
signal range is g00d and n0t easily 0bstructed.

C0ns 0f 802.11g:

                                      C0sts m0re
than 802.11b; appliances may interfere 0n the unregulated signal frequency.


                              802.11n is an amendment that impr0ves up0n the previ0us
802.11 standards by adding multiple-input multiple-0utput antennas
(MIM0). 802.11n 0perates 0n b0th the 2.4 GHz and the 5 GHz bands.
Supp0rt f0r 5 GHz bands is 0pti0nal. It 0perates at a maximum net data
rate fr0m 54 Mbit/s t0 600 Mbit/s. The IEEE has appr0ved the
amendment, and it was published in 0ct0ber 2009.Pri0r t0 the final ratificati0n,
enterprises were already migrating t0 802.11n netw0rks based 0n the Wi-Fi
Alliance’s certificati0n 0f pr0ducts c0nf0rming t0
a 2007 draft 0f the 802.11n pr0p0sal.

Pr0s 0f 802.11n:

                           Fastest maximum
speed and best signal range; m0re resistant t0 signal interference fr0m 0utside

C0ns 0f 802.11n:

                              Standard is n0t yet finalized; c0sts m0re than
802.11g; the use 0f multiple signals may greatly interfere with nearby
802.11b/g based netw0rks.









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