2 Wireless Presentation Search (1)

8/6/2019 2 Wireless Presentation Search (1)

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Wireless LAN

(WLANs)


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Local Wireless Technologies

Physical-Layer Transm ission- Uses radi o transmissi o n

-Gi

ves m o bility


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Wireless availability

43 ,850 lo @l ions in 2003 .

Est imated in 2004 to grow to over 200 ,00locat ions in 2008 . ( actua lly grew to 10 1 ,0commercial WiF i by end of 2005 )

25 mi llion WiF i routers sh ipped in 2005

J 2006 186 US i i h W i l


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Wireless LAN (WLAN) Access P

La rge Wired Etljnet LAN

Ethernet Sw itch

S

W irelessAccess

Po int

- - -UTP Rad ioTransm is

Commun icat ion

Wire less access


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Access Router w ith Wireless AccessWireless NICs

Access Ro uterw ith Access Po int

PC CardWN IC

for a NotebookComp uter


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Local Wireless Technologies,Continued

802.11

- The dominant W LAN te chnology today

- Standardized by the 802 .1 1 Working Gr


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802.11 Wire less LANs

- Speeds up to tens of megabits per sec o n

distances of 30 to 100 meters o r mo re Can serve man y users in a h ome o r o

- Soo n to be 100 Mbps to 600 Mbps with 8


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802.11 WLAN Standa


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Spec ific 802. 11 Wire less LAN Sta n dards

~

I~ I

S02. 11a S02. 11b S02. 11

Un lic e ns ed Ba nd 5 G Hz 2.4 G Hz 2.4 G H

Crowded Ba n d? No Yes Yes

A i Hi h L L


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Specific 802.11 Wireless LAN Standa

Sou rce fo r throughp ut da ta: B

80 2 .1 1a. ope ra t ing a ta h ighe r freque nc y,

has mo re a tte nu ation S02. 1 1a S02. 1 1 b S02. 1Tha n 8 0 2.1 1b

Ra ted Speed '" 54 Mbps 11 Mbps 54 Mbp


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Specif ic 802 .11 W ireless LAN S

S02 .11a S02 .11 b S02 .1

Ra te d Speed 11 Mbps 54 Mbps 54 M

Th h 30 12 Mb 6 Mb 20 M


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Specif ic 802.11 W ireless LAN St

S02 .11b S02 .11a S02. 1

Un lic e ns ed Band 2.4 GHz ~ GHz 2.4 GH

N b f N


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A new Wireless LAN Standard

A separate standard , 802.16 (or WiMAXtransm its at 70 Mbps and has a range ofmiles.

It can operate in licensed or un licensed bathe spectrum from 2-6 GHz. W iMAX typ imultiple 802. 11 networks or sends Internet dover long d istances.


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Wireless LA

(WLANs)cont


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Bluetooth

- For personal area networks (PANs )

Multiple devices carried by a person, or Multiple devices around a q:;''jk

Limited to about 10 meters


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Local Wireless Technologies, Continu

Other Local Wire less Techno logies- Ul tra wideband : up to 250 Mbps (fast ) over

10 meters (short)- Idea l for v ideo netwo rking in homes

- Zig8ee for almost-always-off sensor networks speeds

- Allows battery lives of months or years


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Local Wireless Technologies, Continue

Other Loca l Wireless Technolog ies

Host

A

- Mesh networking: multiple access points caframes t o their destination wi th ou t using a w

- Being standardized at 802 .11s

E


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Radio Propagation orHow wireless data gets th

, , ,

'1\ :. ' , ' ~ ..

'" , + . ~ ,

, . . ...... . . . . . . . .


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Frequency Measurement

Frequency

- Light waves are measured in wave lengths

- Radio waves are measured in terms of fre

- Measured in hertz (Hz)- t h e number of cocyc les per second


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Frequency Measurement, Continue

Measur ing Frequencies

- Frequenc y measures increases by fact ors o1 ,024)

- Kil ohertz (kHz ) [Note the lower-case k ]

- Megahertz (MH z)

h ( )


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Omnidirectional and Dish Antenna

D ish Anten n a

Focuses s igna ls in a narrow range

l bover

l d

Om n id i re c t ion

Spread s ignals

d l


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Wire less Propagat ion Problems

1.E lectromagnetic

Interference(EMI ) from

" ' ; : : : : - ' Other stat ions,;;.. M c rowave

"::::::::=== ==::::::/ ovens, etc.2.

Attenuat ion: s ignal

weaker w ith d ista

BlocObj


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Wireless Propagation Prob lems

Direct

l h

Blo c

( .............. _ _ O bj


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Inverse Square Law Attenuation

Inverse square law attenuation

- To c o mpare relati ve p ow er at two distances

Divide the lo nger distance by the sh o rte

Square the result ; this is the relati ve p ow

- Examples

100 mW (milliwatts ) at 10 meters


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Frequency-Dependent PropagationProblem

Some problems are Frequenc y-Dependen

- Higher-frequenc y signals attenuate faster

Abs

orbed m ore

rapidl y by waterin

the ai- Higher-frequenc y signals bl ocked m o re by

At low er frequencies , signal refract (bendan b


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The Frequency Spectrum , Serv iceChannels

1.FrequencySpectrum(0 Hz toIn finity) _

2.

Serv iceBand

(F M Rad io,

4.S ignals in d ifferen t chann

inte rfe re w ith one a

Channel 5, S ignal A

Channe l 4, S igna l D

Channel 3, S ignal B


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Channel Bandwidth andTransmission Speed

Shannon Equation- Specifies the c o nnecti o n bet w een channel

and the channel 's ma ximum signal transmissi

- C = B [ Lo g 2 (1 +S /N) 1

C = Ma ximum p o ssible transmissi o nspeed in the channel (bps )


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Shannon Equation

- C = B [Log2 (1+S IN) 1

No te that d o ubling the bandwidth doubles tmaximum possible trans missi o n speed

Increasing the bandwidth by X increasesmaximum possible speed by X


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Broadband and Narrowband Channels

- Broadband means wide channel bandwid

therefore high speed

- Narrowband means narrow channel bandthe re fo re low speed


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Channe l Bandw idth and Spectrum Scar

- Why not ma ke all channels broadband?

- There ison

ly a limited amount of spectrum afrequencies

- Making each channel broader than neededhaving fe we r channels or w idening the serv


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The Golden Zone

- Mo st o rganizati o nal radi o techn o logiesgo lden z o ne in the high megahertz to lorange

- At higher frequencies ,p ro pagati o n p ro blems

High e r Fr


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Spread Spectrum Transmission

Un licensed Bands- W LANs operate in unlicensed service ban

You do not need a license to have ostations

You must tolerate interference from

You must not cause unreasonable interfe


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Spread Spectrum Transmission, Cont

Sprea d Spectrum Transmission

- Yo u are REQ UIRED BY LAW to use spreatransmissi o n in unlicensed bands

Spread spectrum transmissi o n is requirp ro pagati o n problems at high frequencies

Espec ially multi path interference

N l R di d


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Normal Radio Transmission andSpectrum Transmission

Normal transm iss ion: Uses on ly the channe l barequ ired by your s igna ling speed

Channel Bandw idth , _____________Requ ired fo r S igna l I

Speed ' - - - - - - - - - -

N o rma l Ra d io :

Bandwidth Is No

Note: He ight of Box Indicates Ban

Normal Radio T i i and


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Normal Radio Transmission andSpectrum Transmission

Spread spectr um transm iss ion:Uses c ha nn els much wider than s ignal ing speed

Channel Bandw idth ,---_ _ _ _ _ _ _ _ _ _ _ _ _Requ ired for S igna l

Speed

Spread Spe c trumTran s mi ss io n:

Channe l Ba ndw idth

Note: He ight of Box Ind icates Band


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802.11 WLAN Ope

T i l 802 11 WLAN O ti


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Typical 802.11 WLAN Operation

Ethe rne tSw itc h

802 .3 Fra me 1802 . t t Fra

802 .3 Fra me

C lie nt PC

WA PRad

Trans

mi

Wireless access p(WAPs ) bridge t

T i l 802 11 WLAN O i


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Typical 802.11 WLAN Operation

Ethernet

UTP

802.3 Frame

Client PC

WAP

A~ - - ~

WAP

802 .11 Fram

Hando(if mob

Stations and Access Po ints Transmit


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Stations and Access Po ints TransmitChannel

o " ,, , , , , , ' " ~Sw itch / '.:..'i

/ L'p

tccessPointB ~ Coll is ion if 2Dev ices sendS imultaneous ly

di A C l


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Media Access Control

On ly one station or the access point caa t ime

To control access (transmission) , two mbe used

- CSM Al CA+ACK (mandat o ry )

- RTS /CTS (o pti o nal unless 802.11 band 9

CSMA/CA in 802 11 Wireless LA


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CSMA/CA in 802.11 Wireless LA

CSMAICA (Carrier Sense Mu ltiplewith Coll is ion Avoidance)

CSMA- Sender A lwa ys Li stens f o r T raffic

Ca rrier is the s igna l; sense is t o l

- If the re is t raffic , the sende r wa its

80 l


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CSMAICA in 802.11 Wireless LANs

CSMAICA (Carrier Sense Mu ltiple AColl ision Avoidance )

- If there is no traffic

If the time since the last transmissi oa critical value , the stati on sets a randand waits

CS A CA i 802 11 i l


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CSMAICA in 802.11 Wireless L

ACK (Acknowledgement)

- Receiver immediately sends back anacknowledgment when it receives a fram

Does not wai t to send an ACK

Th is avoids in terference with othe r stmust wa it

R t t S d/Cl t S d


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Request to Send/Clear to Send(RTS/CTS)

Client PC

- j RTS f-

Rad ioAccess LinkPOint B

Request to Send/Clear to Send


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Request to Send/Clear to Send(RTS/CTS)

Cl ient PC

CTS

WAP

l

- - - - - -Rad ioLink

"-,.

R


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Recap

CSMAlCA+ACK is m andator y

RTS /CTS is optiona l

- How e ver , it is manda to ry if 802.1 1band 8share the same 802.1 19 access p o int


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Specific 802.11 Wireless LAN S

Transm ission Speed and D istance- As a stati o n m ov es a wa y fro m an access p

transmissi o n speed falls

There are se veral m odes of o perati o n speach standard

The fastest mode o nly wo rks with a ve ry

As the user m ov es a wa y, the signal stren

S ifi 802 11 Wi l LAN


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Specific 802.11 Wireless LAN Continued

Transmiss ion Speed and Distance

- W hen stati o ns transmit mo re slow ly, the ytransmit their frames

This redu ces the time a vailable f o r o thetransmit

Co nsequentl y . th ro ughput falls f o r e ve r


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Fig u re 5-1 9: Int e rf e re n ce Be tw ee n NeaPo int s O p era ti n g o n th e Same C h a nn e

~Access Point A

Chann e l t

"I~Acc e ss Point D

" ~ 4 In 802.t t band Access Point B Interference

802. t tQ Channel 6

nono verlappin

tnterferencehannels are

t , 6 , a n d t t

4 ~ Interference Access Point E

B02 11


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B02.11n

Un d e r De ve lop m e nt- Ra ted s p eeds o f 100 Mbp s to 6 00 Mbp

- W ill op e rat e in both th e2 .4

GHz a nd 5- Ma y use twice curr en t b a ndwidth p e r ch

MHz) to rou ghly doubl e s p eed


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802 . 1 1

Standard for Q ua lity of Serv ice (OoS )

- Nee de d for voice a nd video tra ns miss ion

- W i-F

i Allia nce ca ll

s 802.118Wi -F

i Mu ltim


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WLAN Secur ity

WLAN Security Thre a ts


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WLAN Security Thre a ts

Drive By Ha cke rs- S it ou ts id e th e co rpor a te p re mis e s a nd rea d

traffic

- C a n se nd ma lic io u s tra ffic into th e ne tw o rk- Ea s ily d on e w ith r e a d ily ava ila b le do w n loa d

W ar Dr ivers

WLAN S it Th t C ti


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, WLAN Security Threats, Continu

Rogue Access Po ints

- Unaut ho rized access p o ints set up b y depind ividua l

- Often ha ve ve ry poo r secur ity, ma king d rieas ier

- Often o perate at h igh pow e r, att ra c ting ma


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WLAN Security Threats, Continu

Evil Twin Access Points- C rea te a fake access p o int outside wa lls o

PC

- Leg itima te interna l client associates with taccess point , wh ich opera tes at high power

Leg itimateLeg itimate E


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Evil Twi n Access Po ints- Evil tw in then associates with a legi tima te

access point masqueradi ng as the interna

- Th is connects the evil tw in to the firm's int

Leg itima teLeg itima te

AP

2.Assoc ia tes

As Leg itima te

WLAN Security Threats Continu


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Evi l Tw in Access Points

- Evil tw in can then read all traffic , e ven if threcei ve encr ypt their messages because thsteals authenticati on credentials passed betclients and the legitimate access p o int

- Als o can insert traffic

- C lassic man-in-the-middle attack


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802.11 WLAN Man


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Wireless LAN Management

Access Points Placement in a Bui ld in

- Must be d o ne carefull y fo r goo d c ov erageminimize interference bet ween access p

- La y o ut 3 0-meter t ~ - m e t e rradius c ircblueprints

- Adjust f o r o bvio us p o tential p ro blems such


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Wireless LAN Management

Access Pq i:.:l ts P lace ment in a Bu ild ing

- Insta ll access points and do site surveyssignal quality

- Adjust placement and signal strength according

- Th is is quite expensive

Wi l A P i t M g t


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Wireless Access Point Management

Ethernet SwitchU TP

Ma nageab leWLANSwitch

" " " ' ' ' '

ManageAcce


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. Wireless LAN Management

Remote Access Point Management- Desired func tio nalit y

Co ntinu o us transmissi on qualit y mon

Immediate n otificati o n of failures

Rem ote AP adjustment (power , c hann


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Bl t th P l A N t k


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Bluetooth Personal Area Networks

For Personal Area Networ ks (PANs)- De vices a ro und a desk (co mputer , mo use

printer )

- De vices o n a pers o n 's b ody and nearb y (cPDA , noteb oo k c o mputer , etc. )


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Bluetooth Personal Area Networks (P

Cab le Rep lacement Techno log y- Fo r e xample , w ith a Bluet oo th PD A, print

nearb y Bluet oo th-enab led printer

- No a cc ess p o in ts are used

Direct de vice- to-de vice co mmunica ti o n


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Disadvantages Compared to 802.11- Sh o rt distance (10 meters )

- Low speed (3 Mbps , w ith a sl ow er re verse

- Insufficient f o r W LAN in a building



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Advantages Comparedto

802.11- Low battery p ow er drain s o lo ng batte ry lif

re c harges

- Applicati o n p ro files Define h ow de vices will wo rk together w

human inte rventi o n S ending print jo bs to printers File s ync h ro nizati o n

Bl h P l A N k


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, Bluetooth Personal Area Networks

B luetooth Trends

- Bluet oo th Alliance is enhancing Bluet oo th

- The ne xt versi o n of Bluet oo th is like ly to g rultra wideband transmissi o n

This sh o uld raise speed t o 100 Mbps (o

Transmissi o n d istance will re main limited

Other Wireless Communication


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Other Wireless Communication

3G Cellu lar phones

Vo lP on wireless

RFID and embedded wire less technocredi tl lD cards

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