business and data communication.ppt

8/18/2019 Business and Data communication.ppt

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Copyright 2007 John Wiley & 7 - 1

Business Data Communicationsand Networking

9th Edition

Jerry Fitzgerald and Alan Dennis

John Wiley & ons! "nc

Virginia F. Kleist, Ph.D.

College of Business and Economics

West Virginia University


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Cha#ter $

Wireless

%ocal Area Networks


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Cha#ter $ 'utline

• ntroduction

• W!"# Com$onents

• W%F

• W&"'

• Bluetooth

• Best $ractice W!"# Design

• m$roving W!"# Performance

• &anagement m$lications


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*rinci#al W%ANs +echnologies

• W%F – IEEE 802.11b

• tandardi7ation started after .22a, *ut finished

*efore, more commonly used than .22a

– IEEE 802.11a

• First attem$t to standardi7ation of W!"#s8 more

com$licated than .22*

– IEEE 802.11g

• W&"'

• Bluetooth

– "lso an EEE standard /01.29


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-ore on the A*s and N"Cs

• : se$arate channels availa*le for /01.22* – "ll devices using an "P must use the same channel

• W!"# functions as a shared media !"#

– educes the interference

– Users can roam from "P to "P• nitially #C selects a channel )thus an "P+

– Based on ;strength of signal< from an "P

• During roaming, if #C sees another "P 5ith astronger signal, attaches itself to this "P

• Usually a set of "Ps installed to $rovidegeogra$hical coverage and meet traffic needs

– #Cs selects a less *usy channel if its current channel*ecomes *usy )too many users+


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W%AN +o#ology

" 5ireless "ccess Point )"P+ connected

into an Ethernet 5itch

ame as Ethernet• Physical star • !ogical *us

Use the same radio

fre(uencies, so

ta4e turns using

the net5or4

Uses a #C that

transmits radio

signals to the "P

20Base%= or

200Base%=


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Copyright 2007 John Wiley & 7 -

Antennas used in W%ANs

• -mni directional antennas – =ransmit in all directions simultaneously

– Used on most W!"#s

• Di$ole antenna )ru**er duc4+

– =ransmits in all direction )vertical, hori7ontal, u$,do5n+

• Directional antennas

– Pro>ect signal only in one direction

• Focused area8 stronger signal8 farther ranges

– &ost often used on inside of an e3terior 5all

• =o reduce the security issue

– " $otential $ro*lem 5ith W!"#s


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+y#es o, Antennas


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W%AN .adio Fre/uencies

• W!"#s use radio transmissions to send data*et5een the #C and the "P

• &ost countries use the 1.? @A7 range and the 9

@A7 range

• =he larger the fre(uency range, the greater the

*and5idth, or ca$acity

• t is im$ortant to ensure that V!"# "Ps do not

conflict 5ith each other

• =herefore, each "P is set u$ to transmit on a

different $art of the 1.? or 9 @A7 fre(uency range


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A W%AN 0sing Di,,erent Channels


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W%AN -edia Access Control

• Uses C&"C" – C" collision avoidance

– " station 5aits until another station is finished

transmitting $lus an additional random $eriod of time

*efore sending anything

• &ay use t5o &"C techni(ues simultaneously

– Distri*uted Coordination Function )DCF+

• "lso called ;Physical Carrier ense &ethod<

– Point Coordination Function )PCF+• "lso called ;Virtual Carrier ense &ethod<

• -$tional )can *e set as ;al5ays


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Distri1uted Coordination Function

• elies on the a*ility of com$uters to $hysicallylisten *efore they transmit

– When a node 5ants to send a message

• First listens to ma4e sure that the transmitting nodehas finished, then

• Waits a $eriod of time longer

• Each frame is sent using sto$%and%5ait "

– By 5aiting, the listening node can detect that thesending node has finished and

– Can then *egin sending its transmission

– "CK#"K sent a short time after a frame is received,

– &essage frames are sent a some5hat longer time after)ensuring that no collision 5ill occur+


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*oint Coordination Function (*CF)

• olves Aidden #ode $ro*lem – =5o com$uters can not detect each others signals

• " com$uter is near the transmission limits of the "Pat one end and another com$uter is near thetransmission limits at the other end of the "Ps range

– Physical carrier sense method 5ill not 5or4

• olution

– First send a e(uest =o end )=+ signal to the "P

• e(uest to reserve the circuit and duration

– "P res$onds 5ith a Clear =o end )C=+ signal,

• "lso indicates duration that the channel is reserved

– Com$uter 5ishing to send *egins transmitting


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"EEE 234566a

• -$erates in a 9 @A7 fre(uency range• =otal *and5idth is :00 &A7

– Faster data rates $ossi*le U$ to 9? &*$s

• , 6, 21, 2/, 1?, :, ?/, and 9? &*$s

• Uses the same to$ology as .22*

• educed range *ecause of higher s$eed

– 90 meters ) 290 feet+

– Aighest s$eed achieva*le 5ithin 29 meter


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"EEE 2345661

• &oderate s$eed net5or4ing in the 1.?@A7range

• =hree channels for indoor use in the U,more or less in other $arts of the 5orld

• Each channel has a ma3imum data rate of22 &*$s, for users close to the center ofthe W!"# %22 &*$s is the norm

• /01.22* suffers less attenuation than/01.22a

• Designed to connect easily to Ethernet


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234566g -edia Access Control

• "lmost the same media and error control$rotocols as .22*

– imilar $ac4et layout, e3ce$t

•

Pream*les and headers transmitted atslo5er s$eeds )u$ to a ma3imum of 22

&*$s+

• Payload transmitted at higher s$eeds )u$ to

a ma3 of 9? &*$s+• Data =ransmission in the Physical !ayer

– ame techni(ues in .22a and .22*


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"EEE 234566n

• tandard under develo$ment

• @oal to $rovide high s$eed 5ireless

net5or4ing

• Uses *oth the 1.? and 9 @A7 fre(uencyranges simultaneously

• Current drafts $ro$ose s$eeds of 200%100

&*$s


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W"7F" as *u1lic "nternet Access

• Wi%Fi 5as intended to *e used for indoormo*ile 5ireless access

• &any $roviders have in air$orts and malls

and other $u*lic $laces• Political issues, not technical, interfere

5ith the large scale $rovision of Wi%Fi

•

Being offered *y some to5ns as 5ell ascarriers


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W"-A8

• Commercial name for family of EEE/01.2 standards

• =5o $rimary ty$es Fi3ed and mo*ile

•

!ogical and $hysical to$ology same as/01.22 and shared Ethernet

• Uses controlled access 5ith a version of/01.22 $oint coordination function

• =5o ty$es

– /01.2d

– /01.2e


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"ssues to consider with W"-A8

• W&"' is a com$etitor to $u*lic accessWi%Fi and cellular $hone service

• W&"' is incom$ati*le 5ith *oth

• Aas an effective range that offers *enefits

• Aas controlled access, version of PDF

• Considera*ly more distance covered 5ith

W&"' over Wi%Fi – /01.2d has a ma3imum real 5orld effective

range of 9 miles, /01.2e is miles


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Bluetooth -edia Access Control• Uses Fre(uency Ao$$ing $read $ectrum )FA+

– "vaila*le fre(uency range )1.?000%1.?/:9+ divided into G6

se$arate 2%&A7 channels

– " data *urst transmitted using one channel, ne3t data *urst

uses the ne3t channel, and so on.

– Channels changed *ased on a se(uence and esta*lished *ythe slave and the master $rior to the data transfers

• 2,00 ho$s or channel changes $er second

– "lso used to minimi7e interference

• " noisy channel avoided eventually

• #ot com$ati*le 5ith /01.22*

– Potential interference $ro*lems )es$ecially if many Bluetooth

devices $resent close to .22* devices+


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E,,ecti:e Data .ates in W%ANs

• &a3imum s$eed in *its the hard5arelayers can $rovide

– De$ends on #ominal data rate, Error rate,

Efficiency of data lin4 layer $rotocol, and

Efficiency of &"C $rotocol

• Error $lays a greater role in W!"#s

– ignificant im$act of interference on

$erformance• Causes fre(uent retransmissions, thus

lo5er data rates


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Data %ink *rotocol E,,iciency

• Factors involved – =y$ical W!"# overhead

• 92%*ytes )5ith a short $ream*le+

– Pac4et si7e

•

Data $ac4ets assume a 2900%*yte for full length• Control $ac4ets "CK#"K $ac4ets

– =ransmission rates

• -verhead *its transmission s$eeds

• Payload transmission s$eeds

• "ssuming a mi3 of short and full length $ac4ets

– /9H average efficiency for /01.22*

– G9H average efficiency for /01.22a and /01.22g


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-AC *rotocol E,,iciency

• Wi%Fi Uses a controlled a$$roach )PCF+ – m$oses more fi3ed delays initially 5hen traffic is lo5

• Due to PCFs $ermission *ased $rocedures

• Users e3$erience fe5 res$onse time delays as longas the total amount of traffic remains *elo5 /9%60Hof ca$acity


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E,,ecti:e .ate Estimates


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Costs

•

/01.22g – #e5er technology, 5ill re$lace /01.22a and *

– Costs 5ill dro$ here over time

• W%F and Wired Ethernet

– =he data rates for W%Fi are similar to the effective ratesfor 5ired Ethernet net5or4s

– Wired 200Base%= $rovides a good tradeoff on cost vs.$erformance

– But, Wi%Fi may add mo*ility feature for less 5iring costin e3isting *uildings

– &any traditional net5or4s are using com*ination of*oth to meet the needs of users


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Best *ractice .ecommendations

• "do$t /01.22g – Will re$lace /01.22* and .22a

– Prices of .22g #Cs and "Ps coming do5n

• Wireless vs. Wired

• imilar data rates for lo5 traffic environment

• When mo*ility im$ortant /01.22g

• Using W!"# as an ;overlay net5or4,< or in

con>unction 5ith a 5ired !"#

– W!"#s installed n addition to 5ired !"#s

– =o $rovide mo*ility for la$to$s

– =o $rovide access in hall5ays, lunch rooms, other sites


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*hysical W%AN Design

• &ore challenging than designing a traditional !"# – Use a tem$orary "P and la$to$ to evaluate $lacement of

"Ps

– !ocations are chosen to $rovide coverage as 5ell as tominimi7e $otential interference

• Begin design 5ith a site survey, used to determine

– Feasi*ility of desired coverage

• &easuring the signal strength from tem$orary "Ps

– Potential sources of interference

• &ost common source #um*er and ty$e of 5alls

– !ocations of 5ired !"# and $o5er sources

– Estimate of num*er of "Ps re(uired


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*hysical W%AN Design

• Begin locating "Ps – Place an "P in one corner

– &ove around measuring the signal strength

– Place another "P to the farthest $oint of coverage

•

"P may *e moved around to find *est $ossi*le s$ot• "lso de$ends on environment and ty$e of antenna

– e$eat these ste$s several times until the corners arecovered

– =hen *egin the em$ty coverage areas in the middle

• "llo5 a*out 29H overla$ in coverage *et5een "Ps

– =o $rovide smooth and trans$arent roaming

• et each "P to transmit on a different channel


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-ultistory W%AN Design

• &ust include – Usual hori7ontal ma$$ing, and

– Vertical ma$$ing to minimi7e interference from "Ps on

different floors


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W%AN ecurity

• Es$ecially im$ortant for 5ireless net5or4 – "nyone 5ithin the range can use the W!"#

• Finding a W!"#

– &ove around 5ith W!"# e(ui$$ed device andtry to $ic4 u$ the signal

– Use s$ecial $ur$ose soft5are tools to learn

a*out W!"# you discovered

• Wardriving I this ty$e reconnaissance

• Warchal4ing I 5riting sym*ols on 5alls to

indicate $resence of an unsecure W!"#


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+y#es o, W%AN ecurity• ervice et dentifier )D+

– e(uired *y all clients to include this in every $ac4et

– ncluded as $lain te3t Easy to *rea4

• Wired E(uivalent Privacy )WEP+ – e(uires that user enter a 4ey manually )to #C and "P+

– Communications encry$ted using this 4ey

– hort 4ey )?0%21/ *its+ Easy to *rea4 *y ;*rute force<

• E3tensi*le "uthentication Protocol )E"P+ – -ne time WEP 4eys created dynamically after login

– e(uires a login )5ith $ass5ord+ to a server


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+y#es o, W%AN ecurity! cont;d

• Wi%Fi Protected "ccess )WP"+ – ne5 standard

– longer 4ey, changed for every $ac4et

•

/01.22i – E"P login used to get session 4ey

– uses "E encry$tion


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"m#ro:ing W%AN *er,ormance

• imilar to im$roving 5ired !"#s – m$roving device $erformance

– m$roving 5ireless circuit ca$acity

–

educing net5or4 demand


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"m#ro:ing W%AN *er,ormance

• imilar to im$roving 5ired !"#s – m$roving device $erformance

• f /01.22g 5idely de$loyed, re$lace /01.22* cards5ith .22g cards )may *e the cause for slo5$erformance

• Buy high%(uality cards and "Ps

– m$roving 5ireless circuit ca$acity

• U$grade to /01.22g

• ee3amine $lacement of "Ps

• Chec4 sources of interference )other 5irelessdevices o$erating in the same fre(uencies++

• Use different ty$e of antennas

– educing net5or4 demand


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"m#ro:ing Wireless Circuit Ca#acity

• U$grade to /01.22g• e$lace "Ps

– Fe5est 5alls *et5een "P and devices

– Ceiling or high mounted to minimi7e o*stacles

– -n halls, not in closets

• emove sources of interference

– -ther 5ireless devices o$erating in the samefre(uencies

•

Bluetooth devices, cordless $hones, etc.• Use different ty$e of antennas

– Directional antennas in smaller range to get strongersignals )faster through$ut+


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.educing W%AN Demand

• #ever $lace a server in a W!"# – Dou*les the traffic *et5een clients and server,

once from the client to the "P, and once from

the "P to the server

– !ocate the server in the 5ired $art of the

net5or4 )ideally 5ith a s5itched !"#+

• Place 5ired !"# >ac4s in commonly used

locations – f W!"# *ecomes a $ro*lem, users can s5itch

to 5ired !"# easily


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"m#lications ,or -anagement

• W!"#s *ecoming common $lace – "ccess to internal data, any time, any $lace

• Better $rotection of cor$orate net5or4s

– Pu*lic access through W!"# hots$ots

• Com$etition and overla$ 5ith cell $hone

technologies – #e5 cell $hone technologies )faster, longer ranges+

– Drastic $rice dro$s of W!"# devices

• Wides$read nternet access via multi$licity ofdevices )PD"s, etc,+

– Develo$ment of ne5 nternet a$$lications

• #e5 com$anies created8 some old ones out of*usiness

– Drastic increase in the amount of data flo5ing around


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