Características dos Padrões
e Produtos
IEEE 802.11
Principais Aplicações
Padrões IEEE 802.11
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802.11a
802.11b
802.11c
802.11d
802.11e
802.11f
802.11g
802.11h
802.11i
802.11n
5GHz, 54Mbps
2.4GHz, 11Mbps
Protocolo para bridges
World Mode (Europa 20 dB, EUA-BR 36dB
Qualidade de Serviço
Inter-Access Point Protocol
2.4GHz, 54Mbps, modulação digital OFDM
Seleção dinâmica de frequência
Autenticação e Segurança
Access Point
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Short for Access Point, a hardware device or
a computer's software that acts as a
communication hub for users of a wireless
device to connect to a wired LAN.
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APs are important for providing heightened
wireless security and for extending the
physical range of service a wireless user has
access to.
Infrastructure Mode
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An 802.11 networking framework in which devices
communicate with each other by first going through
an Access Point (AP).
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In infrastructure mode, wireless devices can
communicate with each other or can communicate
with a wired network.
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When one AP is connected to wired network, a set
of wireless stations it is referred to as a Basic
Service Set (BSS).
Infrastructure Mode
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An Extended Service Set (ESS) is a set of
two or more BSSs that form a single
subnetwork.
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Most corporate wireless LANs operate in
infrastructure mode because they require
access to the wired LAN in order to use
services such as file servers or printers.
Ad-hoc Mode
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An 802.11 networking framework in which devices
or stations communicate directly with each other,
without the use of an access point (AP).
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Ad-hoc mode is also referred to as peer-to-peer
mode or an Independent Basic Service Set (IBSS).
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Ad-hoc mode is useful for establishing a network
where wireless infrastructure does not exist or
where services are not required.
802.11
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802.11 refers to a family of specifications
developed by the IEEE for wireless LAN
technology.
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802.11 specifies an over-the-air interface
between a wireless client and a base station
or between two wireless clients.
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The IEEE accepted the specification in 1997.
Specifications in the 802.11 family –
802.11 e 802.11a
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802.11 -- applies to wireless LANs and provides 1
or 2 Mbps transmission in the 2.4 GHz band using
either frequency hopping spread spectrum (FHSS)
or direct sequence spread spectrum (DSSS).
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802.11a -- an extension to 802.11 that applies to
wireless LANs and provides up to 54 Mbps in the
5GHz band. 802.11a uses an orthogonal frequency
division multiplexing encoding scheme rather than
FHSS or DSSS.
802.11b
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802.11b (also referred to as 802.11 High
Rate or Wi-Fi) -- an extension to 802.11 that
applies to wireless LANS and provides 11
Mbps transmission (with 2 and 1 Mbps)
in the 2.4 GHz band.
802.11b
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802.11b uses only DSSS.
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802.11b was a 1999 ratification to the original
802.11 standard, allowing wireless
functionality comparable to Ethernet.
802.11b (Wi-Fi)
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Data Rate: Up to 11Mbps in the 2.4GHz band
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Modulation scheme: DSSS with CCK
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Security: WEP & WPA
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Products that adhere to this standard are
considered "Wi-Fi Certified." Not interoperable
with 802.11a. Requires fewer access points than
802.11a for coverage of large areas.
802.11b (Wi-Fi)
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Offers high-speed access to data at up to 300
feet from base station.
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14 channels available in the 2.4GHz band (only
11 of which can be used in the U.S. due to FCC
regulations) with only three non-overlapping
channels.
802.11a X 802.11b
802.11a
X 802.11b
Velocidade máxima
(Taxa de Dados)
802.11a
802.11b
54 Mbps
11 Mbps
(11, 5.5, 2,
1 Mbps)
(54, 48, 36, 24,18, 12,
6 Mbps)
Real: 28 Mbps
Área
Real: 5.2Mbps
50 Metros
100 Metros
ISM (5 GHz)
ISM (2.4 GHz)
Tecnologia OFDM
Tecnologia DSSS
Banda de Frequência
Modulação
Segurança em redes sem Fio
IEEE 802.11g
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Data Rate: Up to 54Mbps in the 2.4GHz band
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Modulation Scheme:
OFDM above 20Mbps,
DSSS with CCK below 20Mbps
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Security: WEP & WPA & WPA2 (IEEE 802.11i)
IEEE 802.11g
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Pros/Cons & More Info:
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Products that adhere to this standard are considered
"Wi-Fi Certified."
May replace 802.11b.
Improved security enhancements over 802.11.
Compatible with 802.11b.
14 channels available in the 2.4GHz band (only 11 of
which can be used in the U.S. due to FCC regulations)
with only three non-overlapping channels.
Bluetooth
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Up to 2Mbps in the 2.45GHz band.
FHSS.
PPTP, SSL or VPN.
No native support for IP, so it does not
support TCP/IP and wireless LAN
applications well.
Not originally created to support wireless
LANs. Best suited for connecting PDAs, cell
phones and PCs in short intervals.
A Pilha de Protocolos 802.11
Camadas Superiores
Subcamada LLC
Camada
de Enlace
Subcamada MAC
IEEE 802
Infravermelho
IEE
802.11
FHSS
802.11
DSSS
802.11a
OFDM
802.11b
HR-DSSS
802.11g
OFDM
Camada
Física
MAC - CSMA/CA
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Short for Carrier Sense Multiple
Access/Collision Avoidance, a network
contention protocol that listens to a network
in order to avoid collisions.
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Unlike CSMA/CD that deals with network
transmissions once collisions have been
detected.
MAC - CSMA/CA
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CSMA/CA contributes to network traffic
because, before any real data is transmitted,
it has to broadcast a signal onto the network
in order to listen for collision scenarios and to
tell other devices not to broadcast.
Camada Física - OFDM
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Short for Orthogonal Frequency Division
Multiplexing, an FDM modulation technique
for transmitting large amounts of digital data
over a radio wave.
OFDM
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OFDM works by splitting the radio signal into
multiple smaller sub-signals that are then
transmitted simultaneously at different
frequencies to the receiver.
OFDM
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OFDM reduces the amount of crosstalk in
signal transmissions.
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802.11a WLAN, 802.16 and WiMAX
technologies use OFDM.
Camada Física - FHSS
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Acronym for Frequency-Hopping Spread
Spectrum. FHSS is one of two types of
spread spectrum radio, the other being directsequence spread spectrum.
FHSS
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FHSS is a transmission technology used
in WLAN transmissions where the data
signal is modulated with a narrowband
carrier signal that "hops" in a random but
predictable sequence from frequency to
frequency as a function of time over a wide
band of frequencies.
Camada Física - FHSS
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The signal energy is spread in time domain rather
than chopping each bit into small pieces in the
frequency domain.
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This technique reduces interference because a
signal from a narrowband system will only affect the
spread spectrum signal if both are transmitting at the
same frequency at the same time.
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If synchronized properly, a single logical channel is
maintained.
Camada Física - FHSS
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The transmission frequencies are determined by
a spreading, or hopping, code.
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The receiver must be set to the same hopping
code and must listen to the incoming signal at
the right time and correct frequency in order to
properly receive the signal.
FHSS
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Current FCC regulations require manufacturers
to use 75 or more frequencies per transmission
channel with a maximum dwell time (the time
spent at a particular frequency during any
single hop) of 400 ms.
Camada Física - DSSS
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Acronym for Direct-Sequence Spread
Spectrum.
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DSSS is one of two types of spread spectrum
radio, the other being frequency-Hopping spread
spectrum.
DSSS
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DSSS is a transmission technology used
in WLAN transmissions where a data
signal at the sending station is combined
with a higher data rate bit sequence, or
chipping code, that divides the user data
according to a spreading ratio.
DSSS
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The chipping code is a redundant bit pattern for
each bit that is transmitted, which increases the
signal's resistance to interference.
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If one or more bits in the pattern are damaged
during transmission, the original data can be
recovered due to the redundancy of the
transmission.
CCK - Complementary Code Keying
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Short for Complementary Code Keying, a
set of 64 eight-bit code words used to encode
data for 5.5 and 11Mbps data rates in the
2.4GHz band of 802.11b wireless networking.
CCK
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The code words have unique mathematical
properties that allow them to be correctly
distinguished from one another by a receiver
even in the presence of substantial noise and
interference.
CCK - Complementary Code Keying
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CCK works only in conjunction with the DSSS
technology that is specified in the original
802.11 standard.
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It does not work with FHSS.
CCK
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CCK applies sophisticated mathematical
formulas to the DSSS codes, permitting the
codes to represent a greater volume of
information per clock cycle.
CCK
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The transmitter can then send multiple bits of
information with each DSSS code, enough to
make possible the 11Mbps of data rather
than the 2Mbps in the original standard.
Wireless Products
IEEE 802.11
L-G700AP > High Speed 2.4GHz
(802.11g) Wireless Access Point
L-G700AP > High Speed 2.4GHz
(802.11g) Wireless Access Point
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Product Features:
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Up to 54Mbps*
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WPA for Enhanced Wireless Security
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Quickly Add Wireless Access to Your Network
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Web-based Configuration and Management
Product Features:
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DWL-2100AP > High Speed 2.4GHz
(802.11g) Wireless 108Mbps Access Point
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Up to 108Mbps*
WPA & 802.1x Authentication
SNMP Management Software Included
Also Work as Point-To-Point Bridge, Point-toMultipoint Bridge, Repeater, Wireless Client.
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Wireless G USB Adapter
Wireless G USB Adapter
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Easily Connect to Your Wireless Network
from Your Desktop or Notebook PC
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Works with 802.11g and 802.11b Wireless
Networks
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Check E-mail, Surf the Web, and Chat with
Friends and Family Online
DWL-G122 > High Speed 2.4GHz
(802.11g) Wireless USB Adapter
DWL-G122 > High Speed 2.4GHz
(802.11g) Wireless USB Adapter
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Product Features:
Up to 54Mbps*
802.11g Standard, 802.11b Compatible
Protect Your Network with WPA and 802.1x
Security
Quick and Easy Setup
WIMAX
IEEE 802.16
IEEE 802.16 (WiMAX)
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Specifies WiMAX in the 10 to 66 GHz range.
OFDM
DES3 and AES
Commonly referred to as WiMAX or less
commonly as WirelessMAN or the Air
Interface Standard,
IEEE 802.16 is a specification for fixed
broadband wireless metropolitan access
networks (MANs).
IEEE 802.16a (Wi-MAX)
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Added support for the 2 to 11 GHz range.
OFDM
3-DES and AES
Commonly referred to as WiMAX or less
commonly as WirelessMAN or the Air
Interface Standard,
IEEE 802.16 is a specification for fixed
broadband wireless metropolitan access
networks (MANs).
Redes sem Fio de Banda Larga
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Empresas de telefonia têm permissão para oferecer
serviços locais de voz e Internet de alta velocidade.
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Há uma grande demanda por estes serviços.
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Problema: estender par trançado categoria 5 ou
cabos coaxial ou de fibra até milhares de
residências é algo dispendioso.
Redes sem Fio de Banda Larga
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O que fazer ?
Rede sem Fio de Banda Larga.
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Como fazer ?
Uma grande antena e antenas nos clientes é
mais fácil e econômico.
Redes sem Fio de Banda Larga
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Empresas de telecomunicações:
Fornecer um serviço de comunicação sem fio
de vários megabits para voz, Internet e filmes
por demanda.
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LMDS foi feito para este fim.
Redes sem Fio de Banda Larga
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Mas, cada concessionária elaborava seu próprio
sistema ...
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Faltava padrões ...
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Impossibilidade de produzir hardware e software em
massa.
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Preços elevados e aceitação baixa.
Redes sem Fio de Banda Larga
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Um padrão de banda larga sem fio era o
elemento-chave que estava faltando.
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IEEE formou um comitê da indústria e
acadêmico para elaborar um padrão.
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IEEE 802.16 (julho de 1999)
Redes sem Fio de Banda Larga
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Padrão IEEE 802.16 final: abril de 2002.
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“Air Interface for Fixed Broadband Wireless
Access Systems”
(Interface Aérea para Sistemas Fixos de
Acesso sem Fio de Banda Larga)
Redes sem Fio de Banda Larga
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MAN (Metropolitan Area Network) sem Fio
ou Loop Local sem Fio.
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Redes sem Fio de Banda Larga:
(Bolcskey et al., 2001)
(Webb, 2001)
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IEEE 802.16 (Eklund et al., 2002)
Comparando 802.11 com 802.16
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802.11 e 802.16 resolvem problemas diferentes.
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802.16 fornece serviço para edifícios e edifícios não são móveis.
Não migram de uma célula para outra.
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802.11 lida com mobilidade, enquanto 802.16, não.
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Edifícios podem ter muitos computadores. A estação final no
802.11 é um notebook.
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Para edifícios, sinal de rádio melhor é essencial.
802.16
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Assim, 802.16 deve usar comunicação full-duplex,
algo que o 802.11 evita para manter baixo o custo
do sinal de rádio (baixo, o custo dos rádios).
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802.16 se estende sobre parte de uma cidade.
Assim, as distâncias envolvidas podem ser de
quilômetros, o que significa que a potência
percebida numa estação-base pode variar de
estação para estação.
802.16
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Essa variação afeta a relação sinal/ruído,
que, por sua vez define vários esquemas de
modulação.
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A comunicação aberta sobre uma cidade
significa que a segurança e a privacidade
são essenciais e obrigatórias.
802.16
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Cada célula 802.16 deve ter muito mais
usuários que uma célula típica 802.11.
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Espera-se que usuários 802.16 utilizem
maior largura de banda que um usuário típico
802.11.
802.16
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Com o 802.16 é necessário mais espectro do que a
banda ISM no 802.11.
802.16 opera na faixa de frequências de 10 a 66
GHz.
802.16 funciona através de ondas milimétricas.
Ondas milimétricas têm propriedades físicas
diferentes das ondas de rádio, mais longas das
bandas ISM.
802.16
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O 802.11 é omnidirecional.
As ondas milimétricas do 802.16 podem ser
concentradas em feixes direcionais.
Ondas milimétricas são absorvidas pela
intempérie (chuva, neve, granizo, nevoeiro,
... ).
802.16
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QoS no 802.16: o padrão foi projetado para para
Internet, telefonia, televisão e uso pesado de
multimídia.
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O 802.11 foi projetado para ser equivalente à
Ethernet móvel.
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O 802.16 pode ser usado para dispositivos
móveis ?