802.11a/b/g Demystified Tutorial - IIT H

1 2 3 4

2221

7

8

15 16

27

17 18

7

11

19 20

5

9 10

14131217

23 24

25

26

802.11a/b/g DemystifiedTutorial

Across Down1. Frameworkofanetwork5. Highestperformingaccess

device6. Heightofacrest8. Pathforsignals9. Publicuse12.DefinesQoSforLANs14.109Hz15.1stammendmentto802.11

17. Formatfortransmittingdata21.OnlyWi-FiPowerPlay22.Improvedin802.11n23.Contiguousfrequencies25.Non-overlappingchannels

for802.11bg26.Maximumammount

ofusers27. Fragmentofdata

2. Filesdividedandscattered3. Circuitrytointerpret

andexecute4. Oppositeoftransmitter 7. One-millioncyclesper

second10.Conveysdatabetween

points11.802.11HighRate

13.Amountofdatasentinagiventime

16.Rateatwhicharepeatingeventoccurs

18.Splitsonebandintomany19.Receive/sendradiosignal20.Xirruslanguage23.Serviceidentifier24.Instituteofengineers

2 ©2008Xirrus,Inc.AllRightsReserved.

802.11n Demystified

ContentsIntroduction............................................................................... 3

StandardsOverview.................................................................... 3

802.11DataRates..................................................................... 4

RFInterferenceIssues................................................................ 4

SpreadingTechniques................................................................. 5

802.11Channels,Capacity,andAllocation................................... 5

802.11b/gChannelReuseandCellPlanning............................... 6

802.11aChannelReuseandCellPlanning................................... 6

ClientandAccessPointInteraction.............................................. 7

FrameFormat............................................................................ 8

Summary................................................................................... 8

LeadingArchitecture................................................................... 9

AboutXirrus............................................................................... 9

©2008Xirrus,Inc.AllRightsReserved. 3

IntroductionThisguidewillprovideanoverviewofthe802.11a/b/gstandard,includingadiscussiononhowthesestandardscompareinregardstobandwidth,availablechannels,andtheimpactofinterferenceoneach.Armedwiththisinformation,youwillbeabletomoreeffectivelyplanyourwirelessnetworkfortodayandthefuture,ensuringthatthedecisionsyoumaketodaywillultimatelybenefityourorganizationoverthelong-term.

Standards Overview

802.11 Frequency Bands

300GHz

FM RadioTV Fixed

SatelliteFixed

SatelliteSpace

Exploration

3KHz

ISM900MHz802.11

UNII Bands5.1-5.8GHz

802.11a

ISM2.4-2.5GHz802.11b/g

ISM: Industrial, Science & Medical UNII: Unlicensed NationalInformation Infrastructure

802.11b/g operate in the 2.4GHz band, while 802.11a operates in the 5GHz band.

802.11n Demystified Tutorial

ManypeoplethinkwirelessLAN,orWi-Finetworking,is a recent technology development. Actually, thefirstWi-Fi standard, 802.11,was ratified almost10yearsagobytheIEEEcommittee,andwasdesignedtooperateinthe2.4GHzunlicensedbandknownasISM,orIndustrial,ScienceandMedical.

A lot of effort went into the development of theMAC protocols and modulation techniques. Theseearly standards used frequency-hopping and directsequencemethods,whichwasagreatstart,however,at that time the most that could be achieved wasabout 2Mbps. These speeds allowed Wi-Fi to getstarted, but itwassoon realized that higher speedtechnologieswouldberequiredifWi-Fiwastobecomemorethanjustanichetechnology.

Changes weren’t too long in coming, with the firstamendment,knownas802.11a,beingratifiedin1999.The 802.11a standard raised the basic data rate to54Mbpsandoperatedinthe5GHzband.Theadditionalbandwidthwasadramaticimprovementinthroughput,andmovingtothe5GHzbandeliminatedmostoftheinterferenceissuesfoundintheexisting2.4space.

Although this was a vast improvement over theexistingtechnology,802.11awasslowinacceptance.Duetotechnicalhurdles,ittookanotheryearandahalf for products to roll out. Additionally, the newertechnologyrequiredchipsetsthatmadetheproductscostprohibitivetomany.TheIEEEwasawareofthisissue and another amendment, 802.11b, was inparalleldevelopment,andwasalsoratifiedin1999.

802.11bsawimmediateacceptanceasitraisedthebandwidthto11Mbpswhileremaininginthe2.4GHzband. The latter was most important, as chipsetsinthisbandweremuchlesscostlytoproduce.Thisaddendum to the 802.11 standard quickly becametheadoptedstandardandovershadowed802.11aformanyyearstocome.

AsWi-Fiwasjumpingfrom2to11Mbps,wiredEthernetclientsweregoing from10 to100andevenhigherbandwidthrates.Wi-Fineededtoraisethebaronceagain—This led to the802.11gaddendum,whichtheIEEEcommitteeratifiedin2001.


Thisnewaddendumcouldbe looselydescribedasa faster versionof802.11b.Amajorprimarybenefitof802.11gwasthatitoffereddataratesupto54Mbps,thesameas802.11a;howeveritwasalsobackwardcompatibleto802.11b.Thismeantthatnotonlywould802.11gdevicesofferhigherspeedswithother802.11gclients,itwouldalsosupportlowerspeedcommunicationswithexisting802.11bclientsandaccesspoints.

Tosupportthisbackwardcompatibility,802.11gdeviceswererequiredtocommunicateinawayandataratethatstationsinthebasicservicesetwouldbeabletounderstand.Inotherwords,ifanaccesspointwastoserveboth802.11band802.11gclients,thenitwouldneedtosendBeaconframesataframedatarateofnohigherthan11Mbps.Ifan802.11bclientassociatedtoan802.11gnetwork,thenall802.11gclientswouldberequiredtounderstandcommunicationatthelowerratesofspeed.

802.11 Data Rates802.11b was able to increase the raw data ratefrom2Mbpsto11Mbpsbyimprovingthemodulationmethod. 802.11b added CCK, or ComplementaryCodeKeying,amoreefficientformofmodulation.ItwasquicklydeterminedthattryingtogethigherdataratesusingCCKwasimpractical,soatechniquecalledOFDM (Orthogonal Frequency Division Multiplexing)wasdeveloped,therebyincreasingratesto54Mbps.Thismethodisusedforboth802.11aand802.11g.

OFDMmade it possible to transmit large amountsof digital data over radio waves by splitting theradiosignal intomultiple,smallersub-signalswhichare then transmitted simultaneously at differentfrequenciestothereceiver.Forthisreason,themorenon-overlapping channels available, the better theperformancewillbefortheclients.

Inadditiontosignalstrength,oneofthekeyissuesinwirelessnetworkingismitigatinginterference.Asdiscussed previously, both 802.11b and 802.11gdevices operate in the 2.4GHz band. Because2.4 is an unlicensed band that is also available toothertechnologies,ahostofotherdevicesoperatehere, including cordless phones, microwaves,Bluetooth devices, etc. In the presence of theseother technologies, Wi-Fi networks can have theircommunicationthroughputseverelyrestricted.

Interference in the air can cause transmissions tobegarbled,whichreducesenduserthroughputandcauses increased latency of data traversing theRFnetwork – greatly compromising voice and videoapplications.Onekeyadvantageto802.11aisthatitoperatesinthe5GHzband,whichcurrentlyisaless

clutteredspectrum.Inaddition,itoffersupto23non-overlappingchannels, thereforeeven if interferenceispresentithasadditionalchannelsitcanmovetotrytoavoidtheinterference.Theadvantageof5GHzisclearwhenyoucomparethistothe2.4GHzband,whichisalreadyclutteredandoffersonlythreenon-overlappingchannels.

Now that dual-band clients and access points arecommonplace, deployments should use the 5GHzrangeasmuchas possible to get the cleaner andgreater spectrum for high-bandwidth applications.Deployingan802.11a/b/ginfrastructureallowsyouto get the best of bothworlds by supporting olderclients in the 2.4GHz band while taking advantageof the cleaner spectrumandmore non-overlappingchannelsof802.11a.

RF Interference Issues


Spreading TechniquesThe 802.11 standards spread data transmissionsacross the full channel bandwidth in two differentways—DirectSequencespreadingandOFDM.The802.11channelbandwidths,orthedifferencebetweentheir highest and lowest occupied frequencies, areall defined tobeabout25MHzwide. It isdesirableto utilize the full width of the channel because itmaximizestheamountofdatathatcanbetransmitted,or,itallowslessdatatobetransmitted,butinamorerobustmanner.

DirectSequencespreading,likethatusedin802.11b,takesadatasignalandspreadsitacrossawiderbandthanitmightnormallyrequirefortransmission,resultinginhighersignal-to-noiseimmunity.Alternately,OFDM,used in 802.11a and 802.11g, divides the channelintomultiple,concurrentlytransmittedsub-carrierstoprovidethehighestdatathroughputpossible.

Channel Bonding

Amplitude

Frequency

OFDMConceptual

OFDM spreads the transmission data across 52 concur-rent subcarriers within the channel. Subcarrier signal peaks occur at neighboring subcarrier nulls, providing orthoganality.

802.11 Channels, Capacity, and AllocationAsdiscussedearlier,both802.11band802.11goperateinthe2.4GHzband,andwhilethereare11channelstochoosefrom,mostof themoverlapwitheachother, leavingonlythreenon-overlappingchannels[typicallychannels1,6and11].Alternately,802.11aoffersupto23non-overlappingchannels.

The total capacity available is significantly different between the three standards, ranging from 33Mbps in802.11b,to162Mbpsin802.11gtomorethan1.2Gigabitsin802.11a.Keepinmindthatinamixedenvironmentof802.11band802.11gclients,theaveragethroughputwillvarygreatlydependinguponthenumberofclientsthatareusingeachprotocol.Itisalsohelpfultonotethatchannelavailabilitydiffersgreatlybycountry,especiallybetweenJapanandtherestoftheworld.

Channel Allocation

ChannelFrequencyfc (MHz) U.S. EU Japan

2.4GHz Channel Allocation

5GHz Channel Allocation


184 4920 X188 4940 X192 4960 X196 4980 X208 5040 X212 5060 X216 5080 X 36 5180 X X X 40 5200 X X X 44 5220 X X X


48 5240 X X X 52 5260 X X X 56 5280 X X X 60 5300 X X X 64 5320 X X X100 5500 X X104 5520 X X108 5540 X X112 5560 X X116 5580 X X


120 5600 X X124 5620 X X128 5640 X X132 5660 X X136 5680 X X140 5700 X X149 5745 X153 5765 X157 5785 X161 5805 X

1 2412 X X X 2 2417 X X X 3 2422 X X X 4 2427 X X X 5 2432 X X X 6 2437 X X X 7 2442 X X X 8 2447 X X X 9 2452 X X X10 2457 X X X11 2462 X X X12 2467 X X13 2472 X X14 2484 X


Sincethereareonlythreenon-overlappingchannelsavailablein802.11band802.11g,itgetsverydifficultto deploy a series of access points while keepingthemseparatedenoughsothattheydonotinterferewitheachother.Iftheyarecloseenoughtodetectorsee other devices operating on the same channel,serious degradation of the overall performance toallWi-Ficlientswillresult.Inan802.11b/gnetwork,access points need to be deployed in a repeatingpatternofthreebecausethebleed-overfortheotheraccesspointsultimatelydegradesperformanceandreducesoverallnetworkcapacity.

What is worth noting here is that because of thelimited number of non-overlapping channels, theshortestdistancebetweencellsonthesamechannelistypicallylessthanasinglecell.Whatthismeansisthateventhoughonpaperitmaylooklikeyouhavecreatedcleanlydefinedcells,theclientsattachingtothesecellsmightactuallybewithinrangeoftwoormoreaccesspointsonthesamefrequency.

Channels & Capacity

802.11b/g

802.11a

Wireless Capacity Comparison

4 5 6 7 81 2 3 9 10 11 2.4GHz ISM BandCh#

Ch# 61 11

Ch#

11 channels are available in the U.S. for 802.11b/g

All 23 channels are non-overlapping.

23 channels are available in the U.S. for 802.11a

Only 3 channels are non-overlapping.

802.11a Capacity23 channels x 54Mbps = 1242Mbps of RF capacity

802.11g Capacity3 channels x 54Mbps = 162Mbps of RF capacity

802.11b Capacity3 channels x 11Mbps = 33Mbps of RF capacity

54Mbps per channel23 channels



149 153 157 16136 40 44 48 52 56 60 64

100 104 108 112 116 120 124 128 132 136 140

5GHz UNII Band

Even though there are 11 channels for 802.11b/g, only three are non-overlapping, while 802.11a offers 23 non-overlapping channels.

802.11a Channel Reuse and Cell PlanningTheissueofchannelreuseandcellplanningisgreatlyreducedin802.11abecausethe5GHzrangeoffersanadditional20non-overlapping channels. Further, becauseof the increase in thenumber of non-overlappingchannels,thedistancebetweencellsonthesamechannelsisatleasttwocells.

802.11 b/g Channel Reuse and Cell Planning


The802.11standarddefinesveryspecificrulesforbothclientsandaccesspointsoperatinginawirelessnetwork. As an example, the open associationprocessgovernsthewayclientsareallowedto jointhenetwork.Criticalinformationsuchassupporteddatarates,clientidentification,andaccessprivilegesaresentbetweentheaccesspointsandtheclients.Oncejoined,additionalrulesexisttoensurethatalldevicesshare themedium ina courteousmanner.This is accomplished using 802.11’s collisionavoidancescheme.

802.11’s DCF, or Distributed Coordination Function,is the commonmethod for defining how all devicesaccess the network. Fundamentally, all devices willsense,ormonitor,theairtoseewhetherit’sbusybeforebeginningatransmission—muchlikepeopledowhencarryingonaconversation.Thisistheheartof802.11—everyoneneedstolistenfirsttomakesuretheairisclearbeforemakingatransmission.Oncetheairisdeterminedtobeavailable,adevicewilltransmit.Thereceivingdevicewill replywith anacknowledgement,whichconfirmstothesendingstationthatthemessagewas cleanly received. If no acknowledgement isreceived,thesendingstationwillassumethemessagewaslostandretrythetransmission.

802.11 Access Points & Client Interaction

DIFS

Carrier Sense Multiple Access

DCF:All devicescoordinate

the medium

Infrastructure BSS and Distribution System

Wireless Medium Access via Distributed Coordination

802.11 Open Association Process

Collision Avoidance

SIFS

Time

Rx Frame Station 1 Tx ACK Rx Frame Station 2 Tx ACKDIFSAP

Tx FrameContention Window Backoff Rx ACKStation 2

Tx Frame Rx ACK DIFSStation 1

Station 2

Station 1

SIFS

Carrier Sense Multiple Access

To DS

From DS

Ethernet DistributionSystem (DS)

Station AP

AP

Probe Request

Probe Response

ACK

Authentication Request

Association Request

Association Response

Authentication Response

ACK

ACK

ACK

ACK

802.11 is a shared medium where all clients must listen to make sure the air is clear before making a transmission.

Client and Access Point Interaction


Frame Format

802.11 Frame Format

To DS & From DS Fields

All Other Frame Control FieldsMore Fragments (MF) 1 = additional fragments to follow0 = last frameRetry1 = this packet is a retransmission0 = this packet is not a retransmissionProtected Frame (Prot Frame)1 = the frame is protected with link layer

security such as WEP or WPA/20 = the frame is transmitted as clear text

More Data (MD)1 = indicates to the stations the AP has at

least one frame buffered for the station0 = no buffered packets in the AP for the station Order1 = strict ordering supported0 = strict ordering not supportedPower Management (Pwr Mgt)1 = station is in power save mode0 = station is active (out of power save mode)

01 = Control 1000–Block Acknowledgement

Request (used for QoS)1001–Block Acknowledgement

(used for QoS)1010–Power Save (PS) Poll1011–Request to Send (RTS)1100–Clear to Send (CTS)1101–Acknowledgment (ACK)1110–Contention Free (CF) End1111–CF-end + CF-ACK10 = Data0000–Data0001–Data + CF-ACK0010–Data + CF-Poll

0011–Data + CF-ACK + CF-Poll0100–Null Data0101–CF-ACK 0110–CF-Poll*0111–CF-ACK + CF-Poll*1000–QoS Data 1001–QoS Data + CF-ACK1010–QoS Data + CF-Poll1011–QoS Data + CF-ACK

+ CF-Poll1100–QoS Null*1110–QoS CF-Poll*1111–QoS CF-ACK + CF-Poll* 11 = Reserved * No data transmitted.

Type & Subtype Field

To DS = 0 To DS = 1From DS = 0 All Management and Control frames. Data frames transmitted Data frames within IBSS (never from a wireless station in an Infrastructure data frames). infrastructure network to the DS.From DS = 1 Data frames received from the DS for a Frames within a wireless station in an infrastructure network. distribution system.

00 = Management0000–Association Request0001–Association Response0010–Reassociation Request0011–Reassociation Response0100–Probe Request0101–Probe Response1000–Beacon1001–Announcement Traffic

Indication Message (ATIM)1010–Disassociation1011–Authentication1100–Deauthentication1101–Action (used for 802.11h

& QoS)

Fragment Number Sequence Number

FrameCtrl

DurationID

FrameBody FCSAddress 1 Address 2 Address 3 Seq Address 4 Protocol Type Subtype To

DSFromDS MF Retry Pwr

Mgt MD ProtFrame Order

Protocol Field = 00

Address 1 Field Used by the receiver.

Address 2 FieldUsed by the transmitter.

Address 3 FieldUsed by the receiver for filtering.

Network Allocation Vector (Duration)

Duration/ID FieldDepending on bits 14-15 (most significant) this field is defined one of three ways:bit 0 bit 15

0

Connection Free Period (CFP) Frames

100000000000000

Power Save-Poll Frames

11AID (Range: 1–2007)

Frame Control

QoS: Quality of ServiceIBSS: Independent Basic Service Set802.11h: Defines dynamic frequency selection (DFS) for spectrum management and transmit power control (TPC) for power management in the 5GHz band.

Sequence Number (Seq No) Field

Address 4 FieldAdditional addressing used to traverse the Distribution System.

Frame Body FieldThis is also known as the data body or packet payload. Higher level protocols and/or user application data reside in this field (length can be 0–2312 bytes).

Frame Check Sequence (FCS) FieldThe FCS is often referred to as the cyclic redundancy check (CRC). It allows stations and APs to check the integrity of received frames.

An 802.11 frame looks much like other networking standards -- it has detailed definitions on frame formats for the wireless medium.

SummaryTo summarize, 802.11 is a mature standard thathasbeenadoptedandisbeginningtoreplacewirednetworks as the edge of the network. Wi-Fi willcontinue tobe the industrystandard for localareawireless technology for the foreseeable future andwillcontinuetoevolveintofuturestandards,suchas802.11n,whichwill offer anorder ofmagnitude inhigherthroughput.

Whenlookingatanewdeployment,oranextensionofacurrentone,makesureyoudeployonly802.11a/b/gcompatible devices. This gives you the backwardcompatibilityyouneedtosupportlegacydevicesandallows you to take advantage of 802.11a’s cleanerspectrum,morenon-overlappingchannelsandhigheroverallthroughput.

An 802.11 frame looks a lot like all networkingstandards — it has detailed definitions on frameformats for the wireless medium. A frame controlfieldatthestartofeachframeidentifiesitaseithera management, control or data frame, as well ascritical information such as retry state and powermanagement status. It also indicates whether theframetransferiswithinthewirelessnetworkorforawiderdistributionsystem.

Followingtheframecontrolfieldisthedurationfield,whichismainlyusedtoindicatehowlongtheframewill beoccupying theair. This helpsother stationswithinthenetworktocoordinatetheirtransmissionswiththeleastamountofcollisions.Otherfieldsintheframeidentifythesourceanddestinationaddressesofthesendingandreceivingstationstoallowproperroutingoftheframe.


Leading ArchitectureXirrus planned for the success ofWi-Fi by develop-ing an award-winning Wi-Fi architecture powerfulenoughtohandlehigh-bandwidthapplicationstodayand modular enough to be upgraded for futureenhancements.

WiththeWi-FiArray,Xirrusdeliverstheonly ‘PowerPlay’architecture inWi-Finetworkingwith themostbandwidth and coverage per cable drop in theindustry. Xirrus Wi-Fi Arrays deliver up to 8x thebandwidthofasingleaccesspointandarecompact,easy-to-install, ceiling-mounted devices. No othercurrent-generation Wi-Fi technology can deliver thebandwidth or throughput of Xirrus Arrays becausetheyarelimitedto2radiosproducingonly108Mbpsofsharedbandwidth.

Xirrus Wi-Fi Array

Redundant Gigabit Ethernet Uplinks

Multiple Wi-Fi Radios Produce864Mbps of Bandwidth

High Gain Directional Antennas Increase Range

SectoredAntenna

SectoredAntenna

Wi-FiRadio

Wi-FiRadio

Wi-FiRadio

Wi-FiRadio

Wi-FiRadio

Wi-FiRadio

Wi-FiRadio

Wi-FiRadio

Wi-FiRadioWi-Fi

Radio

Wi-FiRadio

Wi-FiRadio

Wi-FiRadio

Wi-FiRadio

Wi-FiRadio

SectoredAntenna

SectoredAntenna

SectoredAntenna

SectoredAntenna

SectoredAntenna

SectoredAntenna

SectoredAntenna

SectoredAntenna

SectoredAntenna

Wi-Fi Controller

50% Sector Overlap

EthernetSwitch

SectoredAntenna

No other current-generation Wi-Fi technology can deliver the bandwidth or throughput of Xirrus Wi-Fi Arrays.

By integrating these key components: theWi-Fi controller, Gigabit Ethernet Switch,Gigabit uplinks,multipleaccesspoints,sectoredantennasystem,Wi-Fi stateful firewallandWi-Fi threatsensor intoasingledevice,XirrusArraysareabletoprovideacentrally-managedplatformthatdeliversunparalleledrange,clientcapacityandperformance,alongwithbetterRFmanagementandroamingforvoice,videoanddataapplications—allinasingledevicethatisfullyupgradeableto802.11n.

About XirrusXirrus,Inc.isaprivatelyheldfirmheadquarteredinWestlakeVillage,California.FoundedbythesameteamthatcreatedXircom(acquiredbyIntelin2001),XirrushasdevelopedthenextgenerationinenterprisewirelessLANarchitecturescenteredaroundtheaward-winningArray.

Backed by leading venture capital firms U.S. Venture Partners and August Capital, Xirrus brings a provenmanagement teamandpatentedapproachtodelivering theperformance,scalabilityandsecurityneededtodeployatruewirelessextensionofthewiredEthernetnetworkcapableofdeliveringTriplePlay(voice,video,data)enablement.

Xirrus,Inc.

[email protected]

2101CorporateCenterDriveThousandOaks,CA91320,USA1.800.947.7871TollFreeintheUSA+1.805.262.1600Sales+1.805.262.1601Fax

Copyright©2008,Xirrus,Inc.AllRightsReserved.XirrusandtheXirruslogoaretrademarksofXirrus,Inc.Allothertrademarksbelongtotheirrespectiveowners.Protectedbypatent#USD526,973S.Otherpatentspending.

1 2 3 4

2221

7

8

15 16

27

17 18

7

11

19 20

5

9 10

14131217

23 24

25

26

C

S

S

I

D

M

Z

H

P

A

T

A

A

N

E

N

N

A

I

R

N

C

N

R

N

8

T

C

F

S

R

A

G

M

N

T

R

E

0

X

I

R

I

A

N

R

Y

L

2

U

P

A

8

A

1

X

M

A

S

0

M

8

2

1

1

B

I

C

T

2

P

A

R

I

R

1

L

U

P

R

T

U

1

I

N

E

F

R

E

Q

U

N

C

Y

C

E

O

N

T

R

L

L

O

R

O

S

T

U

I

T

P

U

T

D

C

P

H

R

O

U

G

H

U

T

A

R

E

C

E

I

E

R

V

C

H

C

E

N

O

F

D

M

R

K

G

S

I

N

A

L

A

I

E

E

E

H

E

C

E

T

Z

D

802.11a/b/g Demystified Crossword Puzzle—Answer Key

Across Down1. Frameworkofanetwork5. Highestperformingaccessdevice6. Heightofacrest8. Pathforsignals9. Publicuse12.DefinesQoSforLANs14.109Hz15.1stammendmentto802.1117. Formatfortransmittingdata21.OnlyWi-FiPowerPlay22.Improvedin802.11n23.Contiguousfrequencies25.Non-overlappingchannels

for802.11bg26.Maximumammount

ofusers27. Fragmentofdata

2. Filesdividedandscattered3. Circuitrytointerpret

andexecute4. Oppositeoftransmitter 7. One-millioncyclespersecond10.Conveysdatabetween

points11.802.11HighRate13.Amountofdatasentin

agiventime16.Rateatwhicha

repeatingeventoccurs18.Splitsonebandintomany19.Receive/sendradiosignal20.Xirruslanguage23.Serviceidentifier24.Instituteofengineers

Documents

802.11a/b/g Demystified Tutorial - IIT H