2 wireless presentation search (1)
TRANSCRIPT
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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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Local Wireless Technologies,Continued
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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Local Wireless Technologies,Continued
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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Channel Bandwidth andTransmission Speed
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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Channel Bandwidth andTransmission Speed
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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Channel Bandwidth andTransmission Speed
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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Channel Bandwidth andTransmission Speed
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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WLAN Security Threats, Continu
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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WLAN Security Threats, Continu
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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Bluetooth Personal Area Networks
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
Bluetooth Personal Area Networks
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Bluetooth Personal Area Networks
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