Wireless LAN and IEEE 802

8/12/2019 Wireless LAN and IEEE 802

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Introduction to Wireless LAN and IEEE

802.11Submitted by gc on Mon, 02/18/2013 - 07:39A wireless LAN (WLANorWiFi)is a data transmission system designed to provide

location-independent network access between computing devices by using radio waves

rather than a cable infrastructure [IEEE 802.11 Wireless LANs, Technical paper].

In the corporate enterprise, wireless LANs are usually implemented as the final link

between the existing wired network and a group of client computers, giving these users

wireless access to the full resources and services of the corporate network across a

building or campus setting.

The widespread acceptance of WLANs depends on industry standardization to ensure

product compatibility and reliability among the various manufacturers.

The 802.11 specification [IEEE Std 802.11 (ISO/IEC 8802-11: 1999)]as a standard for

wireless LANS was ratified by the Institute of Electrical and Electronics Engineers (IEEE)

in the year 1997. This version of 802.11 provides for 1 Mbps and 2 Mbps data rates and

a set of fundamental signaling methods and other services. Like all IEEE 802 standards,

the 802.11 standards focus on the bottom two levels the ISO model, the physical layer

and link layer (see figure below). Any LAN application, network operating system,

protocol, including TCP/IP and Novell NetWare, will run on an 802.11-compliant WLAN

as easily as they run over Ethernet.
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Fig 1: "IEEE 802.11 and the ISO Model"

The major motivation and benefit fromWireless LANsis increased mobility. Untethered

from conventional network connections, network users can move about almost without

restriction and access LANs from nearly anywhere.

The other advantages forWLANinclude cost-effective network setup for hard-to-wire

locations such as older buildings and solid-wall structures and reduced cost of

ownership-particularly in dynamic environments requiring frequent modifications, thanks

to minimal wiring and installation costs per device and user. WLANs liberate users from

dependence on hard-wired access to the network backbone, giving them anytime,

anywhere network access. This freedom to roam offers numerous user benefits for a

variety of work environments, such as:

Immediate bedside access to patient information for doctors and hospital staff

Easy, real-time network access for on-site consultants or auditors

Improved database access for roving supervisors such as production linemanagers, warehouse auditors, or construction engineers

Simplified network configuration with minimal MIS involvement for temporary setups

such as trade shows or conference rooms

Faster access to customer information for service vendors and retailers, resulting in

better service and improved customer satisfaction

Location-independent access for network administrators, for easier on-site

troubleshooting and support

Real-time access to study group meetings and research links for students

IEEE 802.11 ArchitectureSubmitted by gc on Mon, 02/18/2013 - 07:40Each computer, mobile, portable or fixed, is referred to as a station in 802.11 [Wireless

Local Area Networks].

The difference between a portable and mobile station is that a portable station moves

from point to point but is only used at a fixed point. Mobile stations access the LAN

during movement.

When two or more stations come together to communicate with each other, they form aBasic Service Set (BSS). The minimum BSS consists of two stations. 802.11 LANs use

the BSS as the standard building block.

A BSS that stands alone and is not connected to a base is called an Independent Basic

Service Set (IBSS) or is referred to as an Ad-Hoc Network. An ad-hoc network is a

network where stations communicate only peer to peer. There is no base and no one

gives permission to talk. Mostly these networks are spontaneous and can be set up

rapidly. Ad-Hoc or IBSS networks are characteristically limited both temporally and

spatially.
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Fig 1: "Adhoc Mode"

When BSS's are interconnected the network becomes one with infrastructure. 802.11

infrastructure has several elements. Two or more BSS's are interconnected using a

Distribution System or DS. This concept of DS increases network coverage. Each BSS

becomes a component of an extended, larger network. Entry to the DS is accomplished

with the use of Access Points (AP). An access point is a station, thus addressable. So,

data moves between the BSS and the DS with the help of these access points.

Creating large and complex networks using BSS's and DS's leads us to the next level of

hierarchy, the Extended Service Set or ESS. The beauty of the ESS is the entire network

looks like an independent basic service set to the Logical Link Control layer (LLC). This

means that stations within the ESS can communicate or even move between BSSs

transparently to the LLC.

Fig 2: Infrastructure Mode


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One of the requirements of IEEE 802.11 is that it can be used with existing wired

networks. 802.11 solved this challenge with the use of a Portal. A portal is the logical

integration between wired LANs and 802.11. It also can serve as the access point to the

DS. All data going to an 802.11 LAN from an 802.X LAN must pass through a portal. It

thus functions as bridge between wired and wireless.

The implementation of the DS is not specified by 802.11. Therefore, a distribution

system may be created from existing or new technologies. A point-to-point bridge

connecting LANs in two separate buildings could become a DS.

While the implementation for the DS is not specified, 802.11 does specify the services,

which the DS must support. Services are divided into two sections

1. Station Services (SS)

2. Distribution System Services (DSS).

There are five services provided by the DSS

1. Association

2. Reassociation

3. Disassociation

4. Distribution

5. Integration

The first three services deal with station mobility. If a station is moving within its own

BSS or is not moving, the stations mobility is termed No-transition. If a station moves

between BSS's within the same ESS, its mobility is termed BSS-transition. If the station

moves between BSS's of differing ESS's it is ESS transition. A station must affiliate itself

with the BSS infrastructure if it wants to use the LAN. This is done by Associating itself

with an access point. Associations are dynamic in nature because stations move, turn on

or turn off. A station can only be associated with one AP. This ensures that the DS

always knows where the station is.

Association supports no-transition mobility but is not enough to support BSS-transition.

Enter Reassociation. This service allows the station to switch its association from one AP

to another. Both association and reassociation are initiated by the station. Disassociation

is when the association between the station and the AP is terminated. This can be

initiated by either party. A disassociated station cannot send or receive data. ESS-transition are not supported. A station can move to a new ESS but will have to reinitiate

connections.

Distribution and Integration are the remaining DSS's. Distribution is simply getting the

data from the sender to the intended receiver. The message is sent to the local AP (input

AP), then distributed through the DS to the AP (output AP) that the recipient is

associated with. If the sender and receiver are in the same BSS, the input and out AP's

are the same. So the distribution service is logically invoked whether the data is going

through the DS or not. Integration is when the output AP is a portal. Thus, 802.x LANs

are integrated into the 802.11 DS.

Station services are:


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1. Authentication

2. Deauthentication

3. Privacy

4. MAC Service Data Unit (MSDU) Delivery.

With a wireless system, the medium is not exactly bounded as with a wired system. Inorder to control access to the network, stations must first establish their identity. This is

much like trying to enter a radio net in the military.

Before you are acknowledged and allowed to converse, you must first pass a series of

tests to ensure that you are who you say you are. That is really all authentication is.

Once a station has been authenticated, it may then associate itself. The authentication

relationship may be between two stations inside an IBSS or to the AP of the BSS.

Authentication outside of the BSS does not take place.

There are two types of authentication services offered by 802.11. The first is Open

System Authentication. This means that anyone who attempts to authenticate willreceive authentication. The second type is Shared Key Authentication. In order to

become authenticated the users must be in possession of a shared secret. The shared

secret is implemented with the use of the Wired Equivalent Privacy (WEP) privacy

algorithm. The shared secret is delivered to all stations ahead of time in some secure

method (such as someone walking around and loading the secret onto each station).

Deauthentication is when either the station or AP wishes to terminate a stations

authentication. When this happens the station is automatically disassociated. Privacy is

an encryption algorithm, which is used so that other 802.11 users cannot eavesdrop on

your LAN traffic. IEEE 802.11 specifies Wired Equivalent Privacy (WEP) as an optional

algorithm to satisfy privacy. If WEP is not used then stations are "in the clear" or "in the

red", meaning that their traffic is not encrypted. Data transmitted in the clear are called

plaintext. Data transmissions, which are encrypted, are called ciphertext. All stations

start "in the red" until they are authenticated. MSDU delivery ensures that the information

in the MAC service data unit is delivered between the medium access control service

access points.

The bottom line is this, authentication is basically a network wide password. Privacy is

whether or not encryption is used. Wired Equivalent Privacy is used to protect authorized

stations from eavesdroppers. WEP is reasonably strong. The algorithm can be broken in

time. The relationship between breaking the algorithm is directly related to the length oftime that a key is in use. So, WEP allows for changing of the key to prevent brute force

attack of the algorithm. WEP can be implemented in hardware or in software. One

reason that WEP is optional is because encryption may not be exported from the United

States. This allows 802.11 to be a standard outside the U.S. albeit without the

encryption.

IEEE 802.11 Standards

Submitted by gc on Mon, 02/18/2013 - 07:44

The most critical issue affecting WLAN demand has been limited throughput.


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The data rates supported by the original 802.11standardsare too slow to support most

general business requirements and slowed the adoption of WLANs.

Recognizing the critical need to support higher data-transmission rates, the IEEE ratified

the 802.11b standard (also known as 802.11 High Rate) for transmissions of up to 11

Mbps.

After 802.11b one more standard 802.11a has been ratified and in January 2002 the

draft specification of another 802.11g has been approved. 802.11g is expected to be

ratified till early 2003.

The letters after the number "802.11" tell us the order in which the standards were first

proposed [Emerging Technology: Wireless Lan Standards]. This means that the

"new" 802.11a is actually older than the currently used 802.11b, which just happened to

be ready first because it was based on relatively simple technology-Direct Sequence

Spread Spectrum (DSSS), as opposed to 802.11a's Orthogonal Frequency Division

Multiplexing (OFDM). The more complex technology provides a higher data rate:802.11b can reach 11Mbits/sec, while 802.11a can reach 54Mbits/sec.

IEEE 802.11b IEEE 802.11a IEEE 802.11g

IEEE 802.11b Submitted by gc on Mon, 02/18/2013 - 07:44 With 802.11b WLANs, mobile users can get Ethernet levels of performance,

throughput, and availability. The basic architecture, features, and services of 802.11b are defined by the

original 802.11 standard. The 802.11b specification affects only the physicallayer, adding higher data rates and more robust connectivity.

The key contribution of the 802.11b addition to the wireless LAN standard wasto standardize the physical layer support of two new speeds,5.5 Mbps and 11Mbps.

To accomplish this, DSSS had to be selected as the sole physical layer techniquefor the standard since, as frequency hopping cannot support the higher speedswithout violating current FCC regulations. The implication is that 802.11bsystems will interoperate with 1 Mbps and 2 Mbps 802.11 DSSS systems, butwill not work with 1 Mbps and 2 Mbps 802.11 FHSS systems.

The original 802.11 DSSS standard specifies an 11-bit chipping?called a Barkersequence?to encode all data sent over the air. Each 11-chip sequence representsa single data bit (1 or 0), and is converted to a waveform, called a symbol, thatcan be sent over the air.

These symbols are transmitted at a 1 MSps (1 million symbols per second)symbol rate using technique called Binary Phase Shift Keying BPSK). In thecase of 2 Mbps, a more sophisticated implementation called Quadrature PhaseShift Keying (QPSK) is used; it doubles the data rate available in BPSK, viaimproved efficiency in the use of the radio bandwidth. To increase the data ratein the 802.11b standard, advanced coding techniques are employed.

Rather than the two 11-bit Barker sequences, 802.11b specifies ComplementaryCode Keying (CCK), which consists of a set of 64 8-bit code words. As a set,
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these code words have unique mathematical properties that allow them to becorrectly distinguished from one another by a receiver even in the presence ofsubstantial noise and multipath interference (e.g., interference caused byreceiving multiple radio reflections within a building).

The 5.5 Mbps rate uses CCK to encode 4 bits per carrier, while the 11 Mbps rate

encodes 8 bits per carrier. Both speeds use QPSK as the modulation techniqueand signal at 1.375 MSps. This is how the higher data rates are obtained. Tosupport very noisy environments as well as extended range, 802.11b WLANsuse dynamic rate shifting, allowing data rates to be automatically adjusted tocompensate for the changing nature of the radio channel. Ideally, users connectat the full 11 Mbps rate.

However when devices move beyond the optimal range for 11 Mbps operation,or if substantial interference is present, 802.11b devices will transmit at lowerspeeds, falling back to 5.5, 2, and 1 Mbps. Likewise, if the device moves backwithin the range of a higher-speed transmission, the connection willautomatically speed up again. Rate shifting is a physical layer mechanism

transparent to the user and the upper layers of the protocol stack. One of the more significant disadvantages of 802.11b is that the frequency band

is crowded, and subject to interference from other networking technologies,microwave ovens, 2.4GHz cordless phones (a huge market), and Bluetooth[Wireless Standards Up in the Air]. There are drawbacks to 802.11b, includinglack of interoperability with voice devices, and no QoS provisions formultimedia content. Interference and other limitations aside, 802.11b is the clearleader in business and institutional wireless networking and is gaining share forhome applications as well.

IEEE 802.11a Submitted by gc on Mon, 02/18/2013 - 07:45 802.11a, is much faster than 802.11b, with a 54Mbps maximum data rate

operates in the 5GHz frequency range and allows eight simultaneous channels[Emerging Technology: Wireless Lan Standards].

802.11a uses Orthogonal Frequency Division Multiplexing (OFDM), a newencoding scheme that offers benefits over spread spectrum in channelavailability and data rate.

Channel availability is significant because the more independent channels thatare available, the more scalable the wireless network becomes. 802.11a usesOFDM to define a total of 8 non-overlapping 20 MHz channels across the 2

lower bands. By comparison, 802.11b uses 3 non-overlapping channels. All wireless LANs use unlicensed spectrum; therefore they're prone tointerference and transmission errors. To reduce errors, both types of 802.11automatically reduce the Physical layer data rate. IEEE 802.11b has three lowerdata rates (5.5, 2, and 1Mbit/sec), and 802.11a has seven (48, 36, 24, 18, 12, 9,and 6Mbits/sec). Higher (and more) data rates aren't 802.11a's only advantage. Italso uses a higher frequency band, 5GHz, which is both wider and less crowdedthan the 2.4GHz band that 802.11b shares with cordless phones, microwaveovens, and Bluetooth devices.

The wider band means that more radio channels can coexist withoutinterference. Each radio channel corresponds to a separate network, or a

switched segment on the same network. One big disadvantage is that it is notdirectly compatible with 802.11b, and requires new bridging products that can
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support both types of networks. Other clear disadvantages are that 802.11a isonly available in half the bandwidth in Japan (for a maximum of four channels),and it isn't approved for use in Europe, where HiperLAN2 is the standard.

IEEE 802.11g Submitted by gc on Mon, 02/18/2013 - 07:45 Though 5GHz has many advantages, it also has problems. The most important

of these is compatibility: The different frequencies mean that 802.11a products aren't interoperable with

the 802.11b base. To get around this, the IEEE developed 802.11g, which shouldextend the speed and range of 802.11b so that it's fully compatible with the oldersystems.

The standard operates entirely in the 2.4GHz frequency, but uses a minimum oftwo modes (both mandatory) with two optional modes [Wireless Standards Upin the Air]. The mandatory modulation/access modes are the same CCK(Complementary Code Keying) mode used by 802.11b (hence the compatibility)

and the OFDM (Orthogonal Frequency Division Multiplexing) mode used by802.11a (but in this case in the 2.4GHz frequency band). The mandatory CCKmode supports 11Mbps and the OFDM mode has a maximum of 54Mbps. Thereare also two modes that use different methods to attain a 22Mbps data rate--PBCC-22 (Packet Binary Convolutional Coding, rated for 6 to 54Mbps) andCCK-OFDM mode (with a rated max of 33Mbps).

The obvious advantage of 802.11g is that it maintains compatibility with802.11b (and 802.11b's worldwide acceptance) and also offers faster data ratescomparable with 802.11a. The number of channels available, however, is notincreased, since channels are a function of bandwidth, not radio signalmodulation - and on that score, 802.11a wins with its eight channels, comparedto the three channels available with either 802.11b or 802.11g. Anotherdisadvantage of 802.11g is that it also works in the 2.4 GHz band and so due tointerference it will never be as fast as 802.11a.

Security


Securityis one of the first concerns of people deploying a Wireless LAN, the 802.11

committee has addressed the issue by providing what is called WEP (Wired EquivalentPrivacy)[A Technical Tutorial on the IEEE 802.11 Protocol, by Pablo Brenner].The main concerns of users are that an intruder would not be able to:

- Access the Network resources by using similar Wireless LAN equipment, and - Be able to capture the Wireless LAN traffic (eavesdropping)

Preventing Access to Network ResourcesThis is done by the use of an Authentication mechanism where a station needs to proveknowledge of the current key; this is very similar to the Wired LAN privacy, on thesense that an intruder needs to enter the premises (by using a physical key) in order to

connect his workstation to the wired LAN.
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EavesdroppingEavesdropping is prevented by the use of the WEP algorithm, which is a PseudeRandon Number Generator (PRNG), initialized by a shared secret key. This PRNGoutputs a key sequence of pseude-random bits equal in length to the largest possible

packet, which is combined with the outgoing/incoming packet producing the packet

transmitted in the air.

The WEP algorithm is a simple algorithm based on RSA?s RC4 algorithm, which hasthe following properties:

Reasonable strong: Brute-force attack to this algorithm is difficult because of thefact that every frame is sent with an Initialization Vector, which restarts thePRNG for each frame.

Self Synchronizing: The algorithm synchronized again for each message, this isneeded in order to work on a connectionless environment, where packets mayget lost (as any LAN).

Competing Technologies to IEEE 802.11


HiperLAN2

HiperLAN2 is a wireless LAN technology operating in the license free 5 GHz (5.4 to5.7 GHz) U-NII band.

Under development by the European Telecommunications Standardization Institute(ETSI) Broadband Radio Access Networks (BRAN) project, HiperLAN2 is designed tocarry ATM cells, IP packets, firewire packets, and digital data from cellular phones.Whereas 802.11a is a form of wireless Ethernet, HiperLAN2 is commonly regarded aswireless ATM.

An extension the 802.11 standard, 802.11a is connectionless Ethernet-like standard,meaning there isnt a persistent connection between client and server. On the other

hand, HiperLAN2 is based on connection-oriented links, though it can accept Ethernetframes. 802.11a is optimized for data communications, as are all standards based on

802.11.

HiperLAN2 is best suited to wireless multimedia because of its integrated Quality ofService (QoS) support. HiperLAN2 will have a difficult time competing with themomentum of 802.11a for several reasons. 802.11a has year head start overHiperLAN2. In addition, the 802.11a group looking for ways to incorporate the bestfeatures of HiperLAN2 within its own standards. It is expected that one mergedEuropean standard will emerge and it will most likely be 802.11a incorporating the bestfeatures of HiperLAN2.


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HomeRF

HomeRF was the first practical wireless home networking technology and came out inmid-2000. HomeRF stands for Home Radio Frequency, as it uses radio frequencies totransmit data over ranges of 75 to 125 feet.

HomeRF uses SWAP (Shared Wireless Access Protocol), which is a hybrid standard,developed from IEEE 802.11. SWAP can connect up to 127 network devices andtransmits at speeds up to 2Mbps.

Overall the major disadvantage to a HomeRF network is data transmission speed. TwoMbps is fine for sharing files and printing normal files. It is insufficient for streamingmedia and printing or transferring large graphic files. HomeRF still provides someadvantages to those wanting a less expensive wired network solution. HomeRF alsodoes not interfere with Bluetooth and is better for transmitting voice signals.

The following table summarizes the major WLAN standards [Research Brief Personalto Global: Wireless Technologies]:

Wireless Local Area Networking Technologies

Application Key Tech Dataspeeds

(Max/Avg)

The Good The Bad The Bottom

Line

Enterprise

Networking

802.11 2 Mbps/ 1.2

Mbps

Wireless local

area

networking

Slow, expensive, poor

security

Good start

but now

superceded

802.11b 11 Mbps/5.5

Mbps

Faster,

cheaper,

stronger than

802.11

Security still not cast

iron, more expensive

than wireline

Viable for

widespread

enterprise

adoption now

802.11g 22 Mbps Faster than

802.11b

Specification not fixed,

competing

technologies coulddivide vendor focus

Should

supersede

802.11bwithin 18

months

Enterprise

and

Metropolitan

Area

Networking

802.11a 54 Mbps/24

Mbps, future

iterations

being planned

to support up

to 100 Mbps

Faster than

802.11b and

802.11g

New modulation

scheme and different

frequency band,

unlikely to be

backward compatible

with 802.11b. No

support for voice in

Available

2002, but

wait 12

months for

cost

reduction
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initial specification.

Costs not proven,

likely to be relatively

expensive

HiperLAN/2 54 Mbps/24

Mbps

Backed by "big

names,"

supports

connection-

oriented

services such as

voice

Likely to be expensive.

Direct competitor with

802.11a; likely to be

the loser in a head-to-

head competition

Will struggle

against

competition

from 802.11a

Home

Networking

HomeRF 2 Mbps/1

Mbps;

planned

future

iterations will

support up to

10 Mbps

Fast, cost-

effective home

networking

standard

Unlikely to be

established outside

home environment

Some

penetration,

but fails to

become

mainstream


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TecMundoInternetWi-Fi Wi-Fi 802.11ac: as redes sem fio de alta velocidade

vm a

Wi-Fi 802.11ac: as redes sem fio de alta

velocidade vm a

Novo padro d os primeiros passos. Confira todas as vantagens que as redes wireless de

velocidade Gigabit vo oferecer.

PorFabio Jordoem 22 de Maio de 2012

H quinze anos, surgiu o primeiro esboo do que seria uma conexo de rede sem fio. Del para c, passamos por diversas modificaes de padro. Mudanas de velocidade,ampliao no alcance do sinal e melhorias em segurana foram algumas das principaisnovidades que tornaram as tecnologias Wi-Fi to populares e essenciais.

Hoje, o padro802.11nimpera na grande maioria dos dispositivos. Mas claro que noparamos no tempo, fato comprovado pelo lanamento dos primeiros dispositivos com atecnologia 802.11ac. So as redes Gigabit que agora ganham a liberdade do wireless.

Neste artigo, vamos explorar as principais mudanas que a quinta gerao sem fio vaioferecer.

Aumento substancial em velocidade

Como em toda mudana de padro, a primeira alterao diz respeito taxa detransferncia. Segundo informao daNetgear,a nova tecnologia wireless garantevelocidade de at 1.300 Mbps na frequncia de 5 GHz, ou seja, mais do que o dobro

da atual especificao que garante produtos operando a at 600 Mbps.

As redes Wi-Fi capacitadas para trabalhar com o padro 802.11ac no operam nafrequncia de 2,4 GHz. Contudo, os dispositivos com a nova tecnologia so compatveiscom redes 802.11n, possibilitando transferncias de dados de at 450 Mbps.

Com tais melhorias, os novos aparelhos roteadores e receptores podem trocar dadospara a transmisso de vdeos em Full HD e com tecnologia 3D. Segundo o site daNetgear,os primeiros aparelhos com a nova especificao podem realizar mltiplasconexes de alta velocidade para transferir esse tipo de contedo.
http://www.tecmundo.com.br/http://www.tecmundo.com.br/http://www.tecmundo.com.br/internet/http://www.tecmundo.com.br/internet/http://www.tecmundo.com.br/internet/http://www.tecmundo.com.br/wi-fi/http://www.tecmundo.com.br/wi-fi/http://www.tecmundo.com.br/wi-fi/http://www.tecmundo.com.br/busca-tecmundo.asp?au=46http://www.tecmundo.com.br/busca-tecmundo.asp?au=46http://www.tecmundo.com.br/busca-tecmundo.asp?au=46http://www.tecmundo.com.br/23229-padrao-de-wi-fi-802-11-ganha-nova-revisao-que-promete-melhorias.htmhttp://www.tecmundo.com.br/23229-padrao-de-wi-fi-802-11-ganha-nova-revisao-que-promete-melhorias.htmhttp://www.tecmundo.com.br/23229-padrao-de-wi-fi-802-11-ganha-nova-revisao-que-promete-melhorias.htmhttp://www.netgear.com/R6300#onehttp://www.netgear.com/R6300#onehttp://www.netgear.com/R6300#onehttp://www.netgear.com/about/press-releases/2012/09262010.aspxhttp://www.netgear.com/about/press-releases/2012/09262010.aspxhttp://www.tecmundo.com.br/http://www.netgear.com/about/press-releases/2012/09262010.aspxhttp://www.netgear.com/R6300#onehttp://www.tecmundo.com.br/23229-padrao-de-wi-fi-802-11-ganha-nova-revisao-que-promete-melhorias.htmhttp://www.tecmundo.com.br/busca-tecmundo.asp?au=46http://www.tecmundo.com.br/wi-fi/http://www.tecmundo.com.br/internet/http://www.tecmundo.com.br/http://www.baixaki.com.br/


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Sinal amplificado e inteligente

As fabricantes que j anunciaram roteadores com o novo padro garantem que um dosprincipais diferenciais da tecnologia o alcance do sinal. Em teoria, os novos aparelhospodem realizar transmisses para computadores ou outros aparelhos que estejam a at

200 metros de distncia. Veja um grfico proposto pelo site5G Wi-Fique compara asvelocidades e os alcances dos padres:

(Fonte da imagem:Reproduo/5G Wi-Fi)

Todavia, o destaque no a cobertura do sinal, mas a qualidade com que ele transmitido. Segundo a informao do site5G Wi-Fi,uma pessoa que esteja a 30 metrosdistncia do roteador receber dados da mesma forma que algum que esteja prximoao aparelho transmissor.

Alm disso, o padro 802.11ac tem uma forma de transmisso inteligente. Em vez depropagar as ondas de modo uniforme para todas as direes, os roteadores wirelessreforam o sinal para os locais onde h computadores conectados. a tecnologiaBeamforming, desenvolvida pelaWavion,que garante comunicao direta entre osdispositivos da rede.
http://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.wavionnetworks.com/Beamforming.htmlhttp://www.wavionnetworks.com/Beamforming.htmlhttp://www.wavionnetworks.com/Beamforming.htmlhttp://www.wavionnetworks.com/Beamforming.htmlhttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.php


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(Fonte da imagem:Reproduo/Netgear)

Vale lembrar ainda que a nova especificao deve reduzir os problemas de pontosmortos, ou seja, locais que antes no recebiam sinal devido ao grande nmero de

barreiras, agora, podem servir como lugares para acesso web. No h muitos detalhesquanto ao funcionamento nesse aspecto, mas tudo indica que o reforo de sinal serresponsvel pela melhoria.

A evoluo do padro

Quando consultamos os sites da Buffalo Tech, da Netgear, da D-Link e da Belkin,encontramos informaes sobre suporte total para transmisso a 1,3 Gbps. Portanto, nodeve haver nada de Draft (compatibilidade razovel com a especificao) no

lanamento.

Os primeiros roteadores compatveis com a especificao 802.11ac devem chegar aindaeste ano. ANetgear,por exemplo, promete que o roteador R6300 vai ser lanado at ofim de maio. Contudo, assim como ocorreu em ocasies anteriores, os primeirosdispositivos podem no oferecer todos os recursos prometidos ou oferecer reduo dequalidade do sinal.

Quanto aos preos, no h como esperar dispositivos de baixo custo. O modelo daNetgear, citado acima, chega s prateleiras custando US$ 199,99. Outros aparelhosdevem seguir a mesma faixa de preo. Por ora, no h previses de lanamento no

Brasil.

O upgrade vlido?

Como o novo padro ainda no est disponvel, no simples definir se a aquisio danova tecnologia algo necessrio. Todavia, considerando os recursos oferecidos,

podemos dizer que um upgrade s pressas pode ser uma pssima jogada.

Ainda que os roteadores 802.11ac ampliem a qualidade do sinal, a velocidade eeliminem alguns defeitos, a velocidade oferecida no oferece benefcios concretos, visto

que a internet brasileira opera com velocidades bem abaixo do que os novos roteadoresconseguem transmitir.
http://www.netgear.com/http://www.netgear.com/http://www.netgear.com/http://www.netgear.com/about/press-releases/2012/09262010.aspxhttp://www.netgear.com/about/press-releases/2012/09262010.aspxhttp://www.netgear.com/about/press-releases/2012/09262010.aspxhttp://www.netgear.com/about/press-releases/2012/09262010.aspxhttp://www.netgear.com/


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Wi-Fi 802.11ac: as redes sem fio de alta

velocidade vm a

Leia mais em:http://www.tecmundo.com.br/wi-fi/23964-wi-fi-802-11ac-as-redes-sem-fio-de-alta-velocidade-vem-ai.htm#ixzz2S90bImmL

H quinze anos, surgiu o primeiro esboo do que seria uma conexo de rede sem fio. Del para c, passamos por diversas modificaes de padro. Mudanas de velocidade,ampliao no alcance do sinal e melhorias em segurana foram algumas das principaisnovidades que tornaram as tecnologias Wi-Fi to populares e essenciais.

Hoje, o padro802.11nimpera na grande maioria dos dispositivos. Mas claro que noparamos no tempo, fato comprovado pelo lanamento dos primeiros dispositivos com a

tecnologia 802.11ac. So as redes Gigabit que agora ganham a liberdade do wireless.Neste artigo, vamos explorar as principais mudanas que a quinta gerao sem fio vaioferecer.

Aumento substancial em velocidade

Como em toda mudana de padro, a primeira alterao diz respeito taxa detransferncia. Segundo informao daNetgear,a nova tecnologia wireless garantevelocidade de at 1.300 Mbps na frequncia de 5 GHz, ou seja, mais do que o dobro

da atual especificao que garante produtos operando a at 600 Mbps.

As redes Wi-Fi capacitadas para trabalhar com o padro 802.11ac no operam nafrequncia de 2,4 GHz. Contudo, os dispositivos com a nova tecnologia so compatveiscom redes 802.11n, possibilitando transferncias de dados de at 450 Mbps.

Com tais melhorias, os novos aparelhos roteadores e receptores podem trocar dadospara a transmisso de vdeos em Full HD e com tecnologia 3D. Segundo o site daNetgear,os primeiros aparelhos com a nova especificao podem realizar mltiplasconexes de alta velocidade para transferir esse tipo de contedo.

Sinal amplificado e inteligente

As fabricantes que j anunciaram roteadores com o novo padro garantem que um dosprincipais diferenciais da tecnologia o alcance do sinal. Em teoria, os novos aparelhospodem realizar transmisses para computadores ou outros aparelhos que estejam a at200 metros de distncia. Veja um grfico proposto pelo site5G Wi-Fique compara asvelocidades e os alcances dos padres:
http://www.tecmundo.com.br/wi-fi/23964-wi-fi-802-11ac-as-redes-sem-fio-de-alta-velocidade-vem-ai.htm#ixzz2S90bImmLhttp://www.tecmundo.com.br/wi-fi/23964-wi-fi-802-11ac-as-redes-sem-fio-de-alta-velocidade-vem-ai.htm#ixzz2S90bImmLhttp://www.tecmundo.com.br/wi-fi/23964-wi-fi-802-11ac-as-redes-sem-fio-de-alta-velocidade-vem-ai.htm#ixzz2S90bImmLhttp://www.tecmundo.com.br/wi-fi/23964-wi-fi-802-11ac-as-redes-sem-fio-de-alta-velocidade-vem-ai.htm#ixzz2S90bImmLhttp://www.tecmundo.com.br/23229-padrao-de-wi-fi-802-11-ganha-nova-revisao-que-promete-melhorias.htmhttp://www.tecmundo.com.br/23229-padrao-de-wi-fi-802-11-ganha-nova-revisao-que-promete-melhorias.htmhttp://www.tecmundo.com.br/23229-padrao-de-wi-fi-802-11-ganha-nova-revisao-que-promete-melhorias.htmhttp://www.netgear.com/R6300#onehttp://www.netgear.com/R6300#onehttp://www.netgear.com/R6300#onehttp://www.netgear.com/about/press-releases/2012/09262010.aspxhttp://www.netgear.com/about/press-releases/2012/09262010.aspxhttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.netgear.com/about/press-releases/2012/09262010.aspxhttp://www.netgear.com/R6300#onehttp://www.tecmundo.com.br/23229-padrao-de-wi-fi-802-11-ganha-nova-revisao-que-promete-melhorias.htmhttp://www.tecmundo.com.br/wi-fi/23964-wi-fi-802-11ac-as-redes-sem-fio-de-alta-velocidade-vem-ai.htm#ixzz2S90bImmLhttp://www.tecmundo.com.br/wi-fi/23964-wi-fi-802-11ac-as-redes-sem-fio-de-alta-velocidade-vem-ai.htm#ixzz2S90bImmL


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(Fonte da imagem:Reproduo/5G Wi-Fi)

Todavia, o destaque no a cobertura do sinal, mas a qualidade com que ele transmitido. Segundo a informao do site5G Wi-Fi,uma pessoa que esteja a 30 metros

distncia do roteador receber dados da mesma forma que algum que esteja prximoao aparelho transmissor.

Alm disso, o padro 802.11ac tem uma forma de transmisso inteligente. Em vez depropagar as ondas de modo uniforme para todas as direes, os roteadores wirelessreforam o sinal para os locais onde h computadores conectados. a tecnologiaBeamforming, desenvolvida pelaWavion,que garante comunicao direta entre osdispositivos da rede.

(Fonte da imagem:Reproduo/Netgear)
http://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.wavionnetworks.com/Beamforming.htmlhttp://www.wavionnetworks.com/Beamforming.htmlhttp://www.wavionnetworks.com/Beamforming.htmlhttp://www.netgear.com/http://www.netgear.com/http://www.netgear.com/http://www.netgear.com/http://www.wavionnetworks.com/Beamforming.htmlhttp://www.5gwifi.org/advantages-of-80211ac.phphttp://www.5gwifi.org/advantages-of-80211ac.php


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Vale lembrar ainda que a nova especificao deve reduzir os problemas de pontosmortos, ou seja, locais que antes no recebiam sinal devido ao grande nmero de

barreiras, agora, podem servir como lugares para acesso web. No h muitos detalhesquanto ao funcionamento nesse aspecto, mas tudo indica que o reforo de sinal serresponsvel pela melhoria.

A evoluo do padro

Quando consultamos os sites da Buffalo Tech, da Netgear, da D-Link e da Belkin,encontramos informaes sobre suporte total para transmisso a 1,3 Gbps. Portanto, nodeve haver nada de Draft (compatibilidade razovel com a especificao) nolanamento.

Os primeiros roteadores compatveis com a especificao 802.11ac devem chegar aindaeste ano. ANetgear,por exemplo, promete que o roteador R6300 vai ser lanado at ofim de maio. Contudo, assim como ocorreu em ocasies anteriores, os primeirosdispositivos podem no oferecer todos os recursos prometidos ou oferecer reduo dequalidade do sinal.

Quanto aos preos, no h como esperar dispositivos de baixo custo. O modelo daNetgear, citado acima, chega s prateleiras custando US$ 199,99. Outros aparelhosdevem seguir a mesma faixa de preo. Por ora, no h previses de lanamento noBrasil.

O upgrade vlido?

Como o novo padro ainda no est disponvel, no simples definir se a aquisio danova tecnologia algo necessrio. Todavia, considerando os recursos oferecidos,podemos dizer que um upgrade s pressas pode ser uma pssima jogada.

Ainda que os roteadores 802.11ac ampliem a qualidade do sinal, a velocidade eeliminem alguns defeitos, a velocidade oferecida no oferece benefcios concretos, vistoque a internet brasileira opera com velocidades bem abaixo do que os novos roteadoresconseguem transmitir.

Leia mais em:http://www.tecmundo.com.br/wi-fi/23964-wi-fi-802-11ac-as-redes-sem-fio-de-

alta-velocidade-vem-ai.htm#ixzz2S90ssCm6
http://www.netgear.com/about/press-releases/2012/09262010.aspxhttp://www.netgear.com/about/press-releases/2012/09262010.aspxhttp://www.netgear.com/about/press-releases/2012/09262010.aspxhttp://www.tecmundo.com.br/wi-fi/23964-wi-fi-802-11ac-as-redes-sem-fio-de-alta-velocidade-vem-ai.htm#ixzz2S90ssCm6http://www.tecmundo.com.br/wi-fi/23964-wi-fi-802-11ac-as-redes-sem-fio-de-alta-velocidade-vem-ai.htm#ixzz2S90ssCm6http://www.tecmundo.com.br/wi-fi/23964-wi-fi-802-11ac-as-redes-sem-fio-de-alta-velocidade-vem-ai.htm#ixzz2S90ssCm6http://www.tecmundo.com.br/wi-fi/23964-wi-fi-802-11ac-as-redes-sem-fio-de-alta-velocidade-vem-ai.htm#ixzz2S90ssCm6http://www.tecmundo.com.br/wi-fi/23964-wi-fi-802-11ac-as-redes-sem-fio-de-alta-velocidade-vem-ai.htm#ixzz2S90ssCm6http://www.tecmundo.com.br/wi-fi/23964-wi-fi-802-11ac-as-redes-sem-fio-de-alta-velocidade-vem-ai.htm#ixzz2S90ssCm6http://www.netgear.com/about/press-releases/2012/09262010.aspx


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Ampliar(Fonte da imagem:Reproduo/AnandTech)

Alm disso, preciso considerar que somente os aparelhos que vo surgir no segundosemestre sero compatveis com a nova especificao. Portanto, de nada adianta investirdesesperadamente em uma tecnologia que pode no trazer benefcios imediatos. Dequalquer forma, vale ficar de olho nos testes e na evoluo de mercado para comprasfuturas.

Fontes de pesquisa:Netgear,5G Wi-Fi,Buffalo Tech,Belkin,D-Link,AnandTech
http://www.tecmundo.com.br/imagens/2012/5/materias/9252510322214487-o.jpghttp://www.tecmundo.com.br/imagens/2012/5/materias/9252510322214487-o.jpghttp://www.anandtech.com/show/5292/80211ac-gigabit-wifi-primerhttp://www.anandtech.com/show/5292/80211ac-gigabit-wifi-primerhttp://www.anandtech.com/show/5292/80211ac-gigabit-wifi-primerhttp://www.netgear.com/landing/80211ac/http://www.netgear.com/landing/80211ac/http://www.netgear.com/landing/80211ac/http://www.5gwifi.org/http://www.5gwifi.org/http://www.5gwifi.org/http://www.buffalotech.com/products/wireless/wireless-routers/airstation-ac1300-n900-gigabit-dual-band-wireless-router-wzr-d1800h/http://www.buffalotech.com/products/wireless/wireless-routers/airstation-ac1300-n900-gigabit-dual-band-wireless-router-wzr-d1800h/http://www.buffalotech.com/products/wireless/wireless-routers/airstation-ac1300-n900-gigabit-dual-band-wireless-router-wzr-d1800h/http://www.belkin.com/pressRoom/releases/uploads/BelkinACBroadcom_051011.htmlhttp://www.belkin.com/pressRoom/releases/uploads/BelkinACBroadcom_051011.htmlhttp://www.belkin.com/pressRoom/releases/uploads/BelkinACBroadcom_051011.htmlhttp://hq.dlink.com/press/http://hq.dlink.com/press/http://hq.dlink.com/press/http://www.anandtech.com/show/5292/80211ac-gigabit-wifi-primerhttp://www.anandtech.com/show/5292/80211ac-gigabit-wifi-primerhttp://www.anandtech.com/show/5292/80211ac-gigabit-wifi-primerhttp://www.tecmundo.com.br/imagens/2012/5/materias/9252510322214487-o.jpghttp://www.anandtech.com/show/5292/80211ac-gigabit-wifi-primerhttp://hq.dlink.com/press/http://www.belkin.com/pressRoom/releases/uploads/BelkinACBroadcom_051011.htmlhttp://www.buffalotech.com/products/wireless/wireless-routers/airstation-ac1300-n900-gigabit-dual-band-wireless-router-wzr-d1800h/http://www.5gwifi.org/http://www.netgear.com/landing/80211ac/http://www.anandtech.com/show/5292/80211ac-gigabit-wifi-primerhttp://www.tecmundo.com.br/imagens/2012/5/materias/9252510322214487-o.jpghttp://www.tecmundo.com.br/imagens/2012/5/materias/9252510322214487-o.jpg

Wireless LAN and IEEE 802

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Transcript of Wireless LAN and IEEE 802