802.11 WiFi Wireless Standards and Facts[1]

8/12/2019 802.11 WiFi Wireless Standards and Facts[1]

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IEEE 802.11 a/b/g/n WiFi Standards and Facts Page 1

Whatis802.11?

The802.11standardsareagroupofevolvingspecificationsdefinedbytheInstituteofElectricaland

ElectronicEngineers(IEEE).CommonlyreferredtoasWiFithe802.11standardsdefineathroughthe

airinterfacebetweenawirelessclientandabasestationaccesspointorbetweentwoormorewireless

clients.TherearemanyotherstandardsdefinedbytheIEEE,suchasthe802.3Ethernetstandard.

Whyarestandardsimportant?

Standardsareasetofspecificationsthatallmanufacturersmustfollowinorderfortheirproductstobe

compatible.Thisisimportanttoinsureinteroperabilitybetweendevicesinthemarket.Standardsmay

providesomeoptionalrequirementsthatindividualmanufacturersmayormaynotimplementintheir

products.

802.11b

In1995,theFederalCommunicationsCommissionhadallocatedseveralbandsofwirelessspectrumfor

usewithoutalicense.TheFCCstipulatedthattheuseofspreadspectrumtechnologywouldberequired

inanydevices.In1990,theIEEEbeganexploringastandard.In1997the802.11standardwasratified

andisnowobsolete.TheninJuly1999the802.11bstandardwasratified.The802.11standardprovides

amaximumtheoretical11Megabitspersecond(Mbps)datarateinthe2.4GHzIndustrial,Scientificand

Medical(ISM)band.

802.11g

In2003,theIEEEratifiedthe802.11gstandardwithamaximumtheoreticaldatarateof54megabitsper

second(Mbps)inthe2.4GHzISMband.Assignalstrengthweakensduetoincreaseddistance,

attenuation(signalloss)throughobstaclesorhighnoiseinthefrequencyband,thedatarate

automaticallyadjuststolowerrates(54/48/36/24/12/9/6Mbps)tomaintaintheconnection.

Whenboth802.11band802.11gclientsareconnectedtoan802.11grouter,the802.11gclientswill

havealowerdatarate.Manyroutersprovidetheoptionofallowingmixed802.11b/gclientsorthey

maybesettoeither802.11bor802.11gclientsonly.

Toillustrate54Mbps,ifyouhaveDSLorcablemodemservice,thedatarateofferedtypicallyfallsfrom

768Kbps(lessthan1Mbps)to6Mbps.Thus802.11goffersanattractivedatarateforthemajorityof

users.The

802.11g

standard

is

backwards

compatible

with

the

802.11b

standard.

Today

802.11g

is

still

themostcommonlydeployedstandard.


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802.11a

Ratificationof802.11atookplacein1999.The802.11astandardusesthe5GHzspectrumandhasa

maximumtheoretical54Mbpsdatarate.Likein802.11g,assignalstrengthweakensduetoincreased

distance,attenuation(signalloss)throughobstaclesorhighnoiseinthefrequencyband,thedatarate

automaticallyadjuststolowerrates(54/48/36/24/12/9/6Mbps)tomaintaintheconnection.The5GHz

spectrumhashigherattenuation(moresignalloss)thanlowerfrequencies,suchas2.4GHzusedin

802.11b/gstandards.Penetratingwallsprovidespoorerperformancethanwith2.4GHz.Productswith

802.11aaretypicallyfoundinlargercorporatenetworksorwithwirelessInternetserviceprovidersin

outdoorbackbonenetworks.

802.11n

InJanuary,

2004

the

IEEE

802.11

task

group

initiated

work.

There

have

been

numerous

draft

specifications,delaysandlackofagreementamongcommitteemembers.Yes,evenintheprocessof

standardsdevelopment,politicsareinvolved.TheProposedamendmenthasnowbeenpushedbackto

early2010.Itshouldbenotedithasbeendelayedmanytimesalready.Thus802.11nisonlyindraft

status.Therefore,itispossiblethatchangescouldbemadetothespecificationspriortofinal

ratification.

Thegoalof802.11nistosignificantlyincreasethedatathroughputrate.Whilethereareanumberof

technicalchanges,oneimportantchangeistheadditionofmultipleinputmultipleoutput(MIMO)and

spatialmultiplexing.MultipleantennasareusedinMIMO,whichusemultipleradiosandthusmore

electricalpower.

802.11nwill

operate

on

both

2.4

GHz

(802.11b/b)

and

5

GHz

(802.11a)

bands.

This

will

require

significantsiteplanningwheninstalling802.11ndevices.The802.11nspecificationsprovideboth20

MHzand40MHzchanneloptionsversus20MHzchannelsin802.11aand802.11b/gstandards.By

bondingtwoadjacent20MHzchannels,802.11ncanprovidedoublethedatarateinutilizationof40

MHzchannels.However,40MHzinthe2.4GHzbandwillresultininterferenceandisnotrecommended

norlikelywhichinhibitsdatathroughputinthe2.4GHzband.Itisrecommendedtouse20MHz

channelsinthe2.4GHzspectrumlike802.11b/gutilizes.Forbestresultsof802.11n,the5GHzspectrum

willbethebestoption.Deploymentof802.11nwilltakesomeplanningeffortinfrequencyandchannel

selection.Some5GHzchannelsmusthavedynamicfrequencyselection(DFS)technologyimplemented

inordertoutilizethoseparticularchannels.

Anotherconsiderationof802.11nisthesignificantlyincreasedelectricalpowerdemandincomparison

tothe

current

802.11b/g

or

802.11a

products.

This

is

primarily

due

to

multiple

transmitters.

TheWiFiAllianceistestingandcertifyingcompatibilityof802.11nradiodraft2.0specifications.There

areseveralrealitiestoconsider.Theyareonlytestingagainstsomebasiccriteriaandinteroperability

points.Alsothenumberofdevicesbeingtestedagainsteachotherislow.Thiscertificationdoesnot

provideanyprotectionagainstchangestothe802.11nstandardpriortoratification.


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VHT

AnIEEEworkinggrouphasbeenworkingoneffortsforthesuccessorto802.11ninthelastoneyear.

ThiseffortisknownasVeryHighThroughput(VHT)andfocusesonchanging802.11tosupport1Gigabit

persecond(Gbps)wirelessLANstandard.

Whichwirelessstandard,802.11b,802.11gor802.11nshouldIbuy?

Today,youwillfindthestoresfullofdraft802.11nproducts.Theestimatesshowthat94%ofthebuyers

oftheseproductsareconsumersorsmallbusinesses,whofranklydontknowaboutstandardsissues.

Themajorityofenterpriseorcorporateusersarenotinvestingintothesedraftproducts.Atissueisboth

thepossibilityoftheseproductsnotbeingcompliantwithanyfinalstandardsandthedesirenotto

sufferpotentialheadachesuntilthetechnologyisfullyready.Interestinglytechnicalwritersfortrade

journalsorthepresstendtopromoteheavily802.11ndespitethefactthatAIR802haspolledits

customersintheUSAandinothercountrieswithover98%reportingthattheyhavenointerestin

802.11nuntilthestandardisratifiedandthetechnologyandproductshavebeenproven.Forreference,

themajorityofAIR802customersaregovernmentagencies;valueaddedresellers,computer

networkingcompanies(installingwirelessproductsinbothresidentialandsmallbusiness

environments),consumersanddistributors.Therefore,itappearsthatmostbuyershavetakenavery

cautiouswaitandseeapproachdespiteoptimisticeditorialarticles.

Forthemajorityofresidentialandsmallandmediumsizebusinessusers,thesinglelargestconcern

amongusersistoprovidethedesiredsignalcoveragefollowedbyreliability.Fortheseuserscurrent

802.11b/gproducts

with

high

RF

power

output

would

provide

the

most

desirable

results.

The

common

consumerequipmentfoundinretailstoreshavebetween30to65mWofRFoutputpower.However,

withinthesamegeneralpricerange,equipmentwith250mWofRFoutputpowerorhighercanbe

purchased.Incomparisontests,highpower802.11b/groutersprovidesignificantlygreaterdistanceand

coverageandasaresulthigherthroughputthananytypicallowerpowered802.11b/gor802.11ndraft

productinthemarket.Formostusersmoredatathroughputisnotacriticaldecisionfactor.Ifthe

wirelessnetworkisbeingusedforInternetaccessandtheDSLorcablemodemservice,whichistypically

lessthan1Mbpsto6Mbpsdependingontheserviceproviderorplan,thetypical25Mbpsdata

throughputonahighRFpowered802.11b/gdeviceismorethansufficient.Infacttoday,thousandsof

networkssupportingIPvideosurveillancearebeingputintoplacewherestreamingcompressedvideois

carriedover802.11gor802.11anetworks.Therealityisthat802.11b/gequipmentwillbeinusefor

many,manyyears.Today,thebulkofequipmentmanufacturedandsoldtowirelessprofessionalsisstill

802.11b/g.


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Forthosefewwhointhenearfutureabsolutelyneedhigherdatathroughputforaparticular

application,then

802.11n

might

be

a

consideration.

The

802.11n

standard

has

been

expected

to

provide

datathroughputof100Mbpsorgreater. However,realworldtests,wherebuildingmaterialsand

existenceofotherwirelesssignalsinthefrequencybandhaveresultedindatathroughputratesofas

lowas26Mbps.Thereisalsotheriskoftheproductbeingoutdatedinayearshouldthespecifications

changethroughtheIEEEworkinggroup. Thustheactualperformancejustmightnotbeanybetteror

muchbetterthanahighRFpowered802.11b/gdevice.

Iffrequencyinterferenceandcongestionisasignificantfactor,then802.11ashouldbeconsidered.

However,notallclientcardsincomputers,etc.have802.11acapabilityandthisshouldbeevaluated

carefully.

Insummary,mostconsumersorsmallbusinesseswouldbebetteroffwithoutanydoubtwithanhighRF

powered802.11b/g

device

for

the

foreseeable

future.

Comparisonof802.11LANStandards

Standard Maximum

DataRate

(Mbps)

Typical

Throughput

(Mbps)

Operating

Frequency

Band

MaximumNon

Overlapping

Channels

(Americas)

802.11b

11

6.5 2.4GHz 3

*1

802.11g 54 8 (Mixedb/g)

25(Only802.11g)

2.4GHz 3 *1

802.11a 54 25 5GHz 24(20MHzchannels)

12(40MHzchannels)

802.11n 248 74*2 2.4GHz&5GHz *3

*1Channels1,6and11arethethreenonoverlappingchannelsintheAmericas.Eachchannelis20

MHzwide.

*2Actualthroughputwilldependuponvariousfactorssuchasthemanufacturerandmodel,

environmentalfactors,whether20MHzor40MHzchannelsareutilized,ifsecurityisenabledand

whetherallclientsare802.11noramixof802.11a/g/n.

*3For802.11n,inthe2.4GHzband,therearethreenonoverlapping20MHzchannelsorone40MHz

channel.Theuseof40MHzisnotdesirableorpracticalinthe2.4GHzband.However,asingle20MHz

channelcouldbeusedwithlowerthroughput,largelydefeatingthegainofusing802.11n.Inthe5GHz

band,twentyfournonoverlapping20MHzoruptotwelve40MHzchannelsexist.


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IEEE802.11b/gChannelAssignments

Channel FrequencyBand

(GHz)

ChannelCenter

Frequency(GHz)

FCCAmericas ETSI(Europe)

1 2.4012.423 2.412 X X

2 2.4062.428 2.417 X X

3 2.4112.433 2.422 X X

4 2.4162.438 2.427 X X

5 2.4212.443 2.432 X X

6 2.4262.448 2.437 X X

7 2.4312.453 2.442 X X

8 2.4362.458 2.447 X X

9

2.4412.463

2.452

X

X

10 2.4462.468 2.457 X X

11 2.4512.473 2.462 X X

12 2.4562.478 2.467 X

13 2.4612.483 2.472 X

14 2.4732.495 2.484

IntheAmericas,withchannels1through11,therearethreenonoverlappingchannels:1,6

and11.


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IEEE802.11aChannelAssignments

DynamicFrequencySelection(DFS)ismandatoryintheAmericasandtheEuropean(ETSI)

market.AccessPoints(APs)mustconstantlymonitorthefrequencyforradarpresence.IftheAP

detectsradar,itisrequiredtoceasealltransmissionswithintherequiredtimeframeand

dynamicallymovetoanotherchannel.

Channel CenterFrequency

(MHz)

Americas ETSI

(Europe)

PermittedUse

Location

Other

Comments

34 5170

36 5180 X X Indoor

38 5190

40 5200 X X Indoor

42 5210

44 5220 X X Indoor

46 5230

48 5240 X X Indoor

52 5260 X X IndoororOutdoor DFSRequired








116

5580

X

X Indooror

Outdoor

DFSRequired







149 5745 X

TypicalOutdoor

153 5765 X

TypicalOutdoor

157 5785 X

TypicalOutdoor

161

5805

X

TypicalOutdoor

165 5825 X

TypicalOutdoor

802.11 WiFi Wireless Standards and Facts[1]

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